With technological advancements enabling globalization, the intercontinental transmission of pathogens has become much easier. Respiratory viruses are one such group of pathogens that require constant monitoring since their outbreak leads to massive public health crises, as exemplified by the influenza virus, respiratory syncytial virus (RSV), and the recent coronavirus disease 2019 (COVID-19) outbreak caused by the SARS-CoV-2. To prevent the transmission of these highly contagious viruses, developing prophylactic tools, such as vaccines, is of considerable interest to the scientific community. Virus-like particles (VLPs) are highly sought after as vaccine platforms for their safety and immunogenicity profiles. Although several VLP-based vaccines against hepatitis B and human papillomavirus have been approved for clinical use by the United States Food and Drug Administration, VLP vaccines against the three aforementioned respiratory viruses are lacking. Here, we summarize the most recent progress in pre-clinical and clinical VLP vaccine development. We also outline various strategies that contributed to improving the efficacy of vaccines against each virus and briefly discuss the stability aspect of VLPs that makes it a highly desired vaccine platform. Respiratory viruses are one of the leading contributors to global mortality. Since the beginning of the 21st century, there have been several respiratory virus outbreaks in the past two decades that were accompanied by disastrous consequences, as evidenced by the recent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. Others, such as the respiratory syncytial virus (RSV) and influenza virus, continue to infect the lower respiratory tracts of individuals, accounting for a significant proportion of global deaths occurring in infants and the elderly . Given tVaccination, one of the greatest medical advancements for human civilization, is widely perceived as the most effective tool for preventing viral infectious diseases. Evidently, with the introduction of vaccines and compulsory vaccination of the general public in 18th and 19th century Europe, there was a drastic decline in smallpox-associated mortality rates . AdvanceInfluenza is a virus belonging to the family Orthomyxoviridae. It is a negative-sense RNA virus subdivided into four different genera: A, B, C, and D. Among these, A and B influenza viruses are of concern as they are capable of causing mortality in humans. These viruses are also capable of infecting other animals, including but not limited to birds, pigs, various vertebrates, and even aquatic animals . On the It is presumed that influenza outbreaks have been prevalent in human society since ancient times. While older literary sources are not as precise as current ones, the information they provided was extremely useful and suggested that influenza virus outbreaks may have occurred more than 2000 years ago. For example, the writings of Hippocrates in 412 BCE describing the “Cough of Perinthus” suggest that this may have been an influenza-like outbreak ,11. WhenSpodoptera frugiperda (Sf9) insect cells. This period was followed by a plethora of studies assessing the efficacy of VLPs expressing HA, NA, or other influenza antigens on the surface of M1 proteins.The development of replication-deficient VLP vaccines against the influenza virus began in the 1990s. One of the earliest influenza VLP constructs was reported to be chimeric. Specifically, Layton et al.  demonstrMacrobrachium rosenbergii nodavirus capsid protein was sufficient to confer protection in BALB/c mice. This chimeric vaccine, without the use of adjuvants, conferred protection against both H3N2 and H1N1 challenge infection [The M2e antigen has been of considerable interest in influenza vaccine development. Fusing multiple copies of the M2 ectodomain has been studied widely, using several virus backbones. Genetically fusing copies of the M2e antigen to the C terminal end of the nfection . Similarnfection . M2e-expnfection . In anotnfection .Much emphasis has been placed on HA antigens, while NA antigens, despite their importance and contribution to protection, continue to be overlooked in influenza vaccine development. Though the number of studies investigating the efficacy of NA VLPs may be lacking, some of these findings were critical to understanding their role as antigens in influenza vaccines. Insect cell-derived VLPs expressing the N1 antigen of the 2009 pandemic H1N1 conferred a broader range of cross-protection than an inactivated split vaccine, which was highly strain-specific. Even in Fc receptor γ-knock out mice, N1 VLP immune sera conferred protection against homologous and heterologous challenge infections . In anot+ and CD8+ T cell responses and were generally better protected [+ regulatory T cell populations was identified in the lungs of mice [Investigating the impact of the VLP vaccines on the aging population is also of concern, and a few research studies investigating this have found interesting results. VLP vaccines were proven to be highly efficacious in aged mice with co-morbidities. Specifically, compared to the mice immunized with the inactivated H1N1 influenza virus, those immunized with the plant-derived H1-expressing VLPs induced greater CD4rotected . Immunizrotected  using pl of mice . AlthougMulti-antigenic VLP vaccines are efficacious against several different strains of influenza viruses. Resultantly, studies examining the protection induced by these bivalent vaccines are prevalent. Baculovirus-derived VLPs expressing the H5 and H7 antigens of avian influenza viruses are one such example. A single dose of this VLP vaccine was sufficient to mount protection in immunized chickens against the highly pathogenic avian influenza virus challenge. Compared to the commercialized trivalent inactivated vaccines, the bivalent VLP vaccine incurred lesser pulmonary pathologies, and much of the lesions and inflammatory responses were alleviated . One stuStudies investigating VLP vaccine-induced protection against influenza B viruses are severely lacking. Because of the emerging influenza B virus-borne infectious cases, VLP vaccine efficacies were evaluated in mice. HA and NA antigens derived from B/Washing/02/2019 Victoria lineage and B/Phuket/3073/2013 Yamagata lineage were used to generate VLPs in Sf9 cells, and these were intramuscularly administered into mice. Interestingly, none of the immunized mice perished upon challenge infection with a lethal dose of B/Colorado/06/2017 Victoria lineage virus, thus signifying the presence of VLP-induced cross-protection against mismatched B virus infections .Although influenza vaccines have been available since the 20th century, they were incapable of preventing viral mutations, and seasonal influenza vaccines remain largely ineffective at times as the strain used in the vaccines failed to match those circulating the world. For this reason, developing a universal vaccine is paramount. Interestingly, the vaccine efficacy of the VLPs displaying the HA antigen of A/California/04/2009 was strikingly different from those of split vaccines. Immunized mice, either with the baculovirus-derived VLPs or split vaccines, were challenge infected with the homologous virus or a heterosubtypic virus A/Philippines/2/82/(H3N2) virus. While VLPs induced better protection against homologous challenge infection, heterosubtypic protection was noticeably higher in mice immunized with the split vaccines .Computationally optimized broadly reactive antigen (COBRA) technology is being explored for influenza vaccine development. The potential for these COBRA-based antigen constructs was demonstrated using ferrets with pre-existing immunity to the H3N2 influenza virus. Here, the mammalian 293T cell-expressed COBRA H3 VLP vaccines conferred broad protection against both the historic vaccine strain and the multiple variants that were co-circulating simultaneously. Furthermore, the COBRA H3 VLPs also elicited greater hemagglutinin inhibition (HAI) and neutralizing antibody titers than VLPs expressing the wild-type H3 antigen . SimilarHeterologous immunization is an interesting concept, and this regimen can improve the efficacy of vaccines. Live-attenuated influenza virus vaccine efficacy could be moderately improved by boosting with baculovirus-expressed VLPs containing the five tandem repeats of the M2e antigen (M2e5x) derived from human, swine, and avian influenza viruses. This immunization regimen enhanced protection against both A/Vietnam/rgH5N1 and A/PR8/H1N1 lethal challenge infections in immunized mice . This M2Because the M2e5x VLPs were weakly immunogenic by themselves, methods to improve their protective efficacy have been explored. BALB/c mice immunized with the Sf9 cell-derived VLPs co-displaying the HA and M2e5x antigens were better protected against reassortant H5N1 avian influenza virus challenge infection than VLPs solely expressing the M2e5x . Using tIncorporating adjuvants to improve VLP efficacy is another strategy. For example, both B-cell activating factor (BAFF) and a proliferation-inducing ligand (APRIL) are tumor necrosis factor (TNF) family ligands that could be used as molecular adjuvants. Genetically engineering baculovirus-derived VLPs to incorporate these molecular adjuvants can improve the protection induced by influenza VLPs. Using this approach, one study reported that fusing BAFF or APRIL to the transmembrane domain of the HA antigens can be an effective inducer of protective immunity against influenza virus challenge infections . IncorpoVLP usage is not strictly limited to antigen delivery or vaccination purposes. These nanoparticles can also be utilized to understand the carefully orchestrated internal processing of influenza antigens in cells, as demonstrated using human monocyte-derived macrophages . VLPs byMutations can be introduced to improve the efficacy of influenza vaccines. By disabling the sialic acid receptor-binding activity of the HA antigen in A/California/07/09 (H1N1) expressed on VLPs, a noticeable increase in vaccine-induced protection was detected in mice. Specifically, antibody responses induced by these plant-derived HA VLPs were much more potent than the wild-type HA-expressing VLPs. Receptor-binding inhibited HA VLPs also incurred less pulmonary inflammation and further reduced the lung virus titer by two log orders lower than the HA wild-type VLPs .Although VLP vaccines are still undergoing clinical evaluation, several strategies to improve VLP manufacturing have been documented. One such strategy is the improvements to down-stream processing of the VLPs. A proof-of-concept study demonstrated that an optimized membrane-based down-stream process could be crucial for influenza VLP vaccine production, especially when looking from an industrial perspective. An optimized membrane-based purification approach enabled approximately 80% product recovery while substantially minimizing production costs and time . DissolvDeveloping a universal influenza vaccine is the ultimate goal for influenza vaccinologists, and one possible solution to this is the induction of broadly neutralizing antibodies (bNAbs), which are capable of binding to almost all HA variants. The presence of a highly conserved antibody binding site in the stem region revealed the feasibility of developing such a vaccine, but this was proven to be strikingly challenging. In short, simply removing the rapidly mutating HA domain that overcrowded the viral surface was difficult . HoweverVLP-based influenza vaccines have been ongoing for more than a decade, and the general trend seems to be that they are well-tolerated in vaccinees. Several clinical trials have been conducted for both avian and human influenza viruses. Plant-derived avian H5N1 VLPs were utilized in Phase 1 clinical trials in healthy adults 18–60 years of age . In this trial, vaccines of all tested doses were well-tolerated in vaccinees with mild to self-limiting adverse events . AnotherClinical trials were also conducted for the A/California/04/2009 (H1N1) pandemic influenza. Interestingly, when using bacterially produced VLPs to immunize human subjects in a Phase I clinical trial, non-adjuvanted VLPs conferred a similar level of immunogenicity and safety profile comparable to that of commercialized vaccines, whereas adjuvanted vaccines failed to meet the pre-determined immunogenicity endpoint . Here, VNicotiana benthamiana by Medicago, Inc. induced a substantial increase in cross-reactive antibody responses that lasted for months [Seasonal influenza VLP vaccines were also subjected to clinical evaluation, as tabulated below . In the r months . These qr months . Recentlr months . In anotr months . Phase 3r months . Despiter months .Orthopneumovirus. Structurally, the virus consists of 10 genes that encode in order the non-structural (NS) proteins NS1, NS2, nucleoprotein (N), polymerase co-factor (P), matrix protein (M), small hydrophobic (SH) protein, attachment glycoprotein (G), fusion glycoprotein (F), transcription processing factors M2-1, M2-2, and the large polymerase subunit (L) [RSV is an antisense single-stranded RNA virus, which is phylogenetically categorized under the family Pneumoviridae, genus unit (L) . Among tunit (L) . The virunit (L) . Furtherunit (L) , with anunit (L) .RSV was first isolated in 1955 at Walter Reed Army Institute of Research in the United States from chimpanzees that were suffering from cold and coryza . The iso+ T cells ex vivo, but the protective efficacy of these self-assembled VLPs against RSV was not investigated. The first VLP study to investigate this aspect was done using the Newcastle disease virus (NDV) VLPs that expressed the ectodomain of RSV glycoprotein (G) fused to the transmembrane and cytoplasmic domains of NDV proteins. VLP constructs based on this method incurred substantially less inflammatory response and pathological damage than the notorious formalin-inactivated VLPs [Research using VLP-based vaccines against RSV infections has only begun fairly recently. The first report of chimeric VLP construct expressing an RSV antigen was described in 2004 by Harvey et al. , whose wted VLPs . Using ated VLPs ,82. Epitted VLPs . Followited VLPs ,85. P22 ted VLPs . Mammalited VLPs .Recently, the importance of the pre-fusogenic (PreF) form of RSV F protein has been reported . Since tAs with baculovirus-derived influenza virus VLPs, multi-antigenic VLPs for RSV have been under development. VLP constructs displaying the tandem repeats of the RSV G protein (Gt) on the surface of influenza M1 protein were evaluated in murine models . These RWhile F and G protein-expressing VLPs were extensively researched, this was not the case for the SH antigen. Many of the SH protein vaccine studies were based on live-attenuated viruses ,98. AlthMaternal immunization to investigate the efficacy of RSV vaccines in infants is a potential immunization strategy, as increasing maternal immunity during pregnancy could extend the induced protection to newborns. So far, only a handful of pre-clinical studies have attempted to investigate the protection elicited by these VLP vaccines using a maternal immunization strategy. To test this, cotton rats were immunized with NDV-based VLPs expressing PreF or PostF antigen along with the RSV G protein. While VLPs expressing both F and G antigens strongly enhanced the pre-existing immunity against RSV in dams irrespective of the pre- or post-fusogenic forms, the boosting effect was significantly greater in dams immunized with the PreF VLPs. This protection was carried on to the pups, as indicated by the lessened lung inflammation following RSV challenge infection . While pRecently, several different mutations were introduced to the PreF-stabilized RSV F protein, and the resulting differences were compared by expressing these different mutants on chimeric NDV VLPs. Interestingly, these alternative versions of the PreF mutants were reported to elicit different populations of RSV F-specific antibody responses . Two of It is widely perceived than VLP-based vaccines are highly immunogenic, and the immune responses induced in animal models may far exceed those elicited by other vaccine platforms. Compared to DNA vaccines expressing the RSV F antigen, insect-derived VLPs expressing the identical antigen generally conferred better protection. Specifically, mice immunized with the RSV F DNA vaccines experienced weight loss and pulmonary inflammation that may have resulted from an influx of plasmacytoid dendritic cells, monocytes, and others . Howeverin vitro, Th1-dominant immunity was detected. Contrastingly, stimulating these cells with FI-RSV vaccines elicited a Th2/Th17-biased immune response with depreciated non-interferon antiviral immune responses [Though etiologically difficult to define as the mechanism of disease enhancements varies between different respiratory pathogens, RSV vaccine-associated enhanced respiratory diseases appear to be characterized by exuberant Th2 immune response in the lungs of primed individuals . Surprisesponses . Consistesponses . The detesponses . This shesponses . Based oCoronaviruses are enveloped positive-sense single-stranded RNA viruses that are phylogenetically categorized under the family Coronaviridae, which can be further subdivided into 4 genera: alpha, beta, gamma, and delta . They arConstruction of the first SARS-CoV-2 VLPs was reported in 2020 by Xu et al. , who demSeveral studies have investigated the immunogenic effects of insect cell-derived chimeric SARS-CoV-2 VLP constructs. Influenza VLPs expressing the codon-optimized full-length S, S1, or S2 subunits were reported to induce virus-specific antibody responses in mice, but the neutralizing antibody responses were mediocre and failed to fully inhibit the virus receptor and ligand binding interaction . ImmunizOnly a limited number of VLP vaccine efficacy studies were performed in non-human primates. Plant-derived VLPs expressing the SARS-CoV-2 S protein were proven to be immunogenic in rhesus macaques but supplementing these vaccines with the CpG adjuvants further enhanced both cellular and humoral immune responses. These findings were accompanied by a substantial reduction in viral titer and the absence of vaccine-associated enhanced disease . Nearly As with all viruses, mutations in the genetic sequences of SARS-CoV-2 result in changes that can have diverse consequences in the viral properties, whether it be antigenicity, transmissibility, or others. Since the initial discovery of SARS-CoV-2 in late 2019, numerous variants possessing distinct mutations in the genetic sequences have emerged. The WHO has stated that one or more of the following three criteria must be met to be considered as VOCs: (1) increased transmissibility or negative changes to the COVID-19 epidemiology, (2) changes to clinical manifestation or virulence in hosts, or (3) reduced efficacy of vaccines and other prophylactic tools . CurrentOnly a small number of studies attempted to investigate the protective efficacy of VLPs against VOCs. In one study, a multi-component approach to VLP construction was employed. Here, the Sf9 insect cell-derived S1 subunit was conjugated to the AP205 bacteriophage via SpyTag/SpyCatcher system, and VLPs generated via this approach ensured potent antibody induction in immunized mice, which strongly neutralized the Wuhan (L008) and the UK (B.1.1.7) alpha variants of the SARS-CoV-2 . CompareContinuous mutations and evolving viruses pose a tremendous challenge to vaccine development. However, VLPs can be used to investigate how specific mutations can alter the protective efficacy of vaccines. In one study, by deliberately introducing mutations resembling those of Omicron or Delta SARS-CoV-2 variants, the authors delineated that mutations in any of the key structural components can have a large impact on the viral particle assembly and their neutralization. Surprisingly, using Omicron-mutated SARS-CoV-2 VLPs, it was revealed that the Omicron variants are 15-fold more likely to evade neutralizing antibody responses in convalescing patients and vaccinated individuals . RecentlWith the SARS-CoV-2 becoming more of a seasonal respiratory disease, as in the case of influenza viruses, continued measures to improve SARS-CoV-2 vaccines are a necessity. To address this, developing vaccines that confer dual protection against both influenza and SARS-CoV-2 would be ideal. Glycosylphosphatidylinositol-anchored SARS-CoV-2 S RBD was fused to the GM-CSF adjuvant, and this was incorporated into influenza VLPs expressing the HA and M1 derived from influenza A/Puerto Rico/8/1934 (PR8). This mammalian cell-derived VLP vaccine conferred protection against both influenza and SARS-CoV-2 virus challenge infection in mice . IncorpoFrom an economical perspective, yeast-expressed VLPs would be the system of choice that meets the aforementioned production criteria. Genetically engineering SARS-CoV-2 RBD not only improved the VLP yields in the yeast production system but also enhanced the immunogenicity of the vaccines in mice. Furthermore, these SpyTag/SpyCatcher-based VLPs induced antibodies which also interacted with SARS-CoV-2 variants of concern and even prevented drastic weight loss in hamsters following challenge infection . SpecifiThe VLPs currently under development could also be used along with the emergency-approved SARS-CoV-2 vaccines. Heterologously immunizing mice with plant-derived VLP vaccine along with the Moderna mRNA-1273 vaccine conferred a high level of virus-specific antibodies. The VLP vaccine used in this study efficiently boosted the B-cells that were primed with the RBD-expressing mRNA vaccines. The prime-boost regimen involving mRNA and VLPs was just as effective when the immunization orders were reversed, that is, priming with VLP and boosting with mRNA .The efficacy of ferritin nanoparticles expressing the S protein of SARS-CoV-2 was recently investigated. A single immunization with these ferritin nanoparticles elicited virus-neutralizing antibody titers in mice, which were at least twofold greater than sera acquired from COVID-19 convalescing patients . AnotherAs with influenza and RSV, FDA-approved SARS-CoV-2 VLP vaccines are currently unavailable. Much of the VLP-based vaccine remains at the preclinical level, with several being evaluated in clinical trials as described elsewhere . Here, wThe ABNCoV2 is a capsid VLP adjuvanted with the MF59. This vaccine expresses the S protein RBD, and vaccines are administered twice through the intramuscular route. The Phase 1 clinical trial for this vaccine was carried out by Radboud University Medical Center  and is currently undergoing Phase 3 clinical evaluation in the United States. CoVLP is another VLP vaccine developed by Medicago Inc. and GlaxoSmithKline. In this VLP vaccine, the pre-fusion stabilized S glycoprotein was modified by replacing its transmembrane and cytoplasmic tail portion with that of HA from A/Indonesia/5/2005 (H5N1) to enhance VLP assembly. Participants were immunized twice with this plant-derived VLP with AS03 or CpG1018 adjuvants. In the Phase 1 trial , co-formulating this VLP with AS03 induced neutralizing antibody titers that were 10-fold higher than those detected from convalescent sera . In the While vaccine-induced protection is important, it is worth noting that many of these efficacious vaccines remain unattainable for numerous countries. Therefore, developing a highly efficacious vaccine that can be scaled to high yields at a low cost is desirable. This is particularly the case for mRNA-based SARS-CoV-2 vaccines. From a structural perspective, RNA is unstable and prone to degradation. Consequently, mRNA vaccines require cold chain logistics and management, which are difficult in developing countries. Fortunately, VLPs could address these limitations. The temperature-stable aspect of VLP vaccines was demonstrated using Cervarix, an FDA-approved VLP vaccine against HPV, which was developed by GlaxoSmithKline. Here, the vaccines retained their stability and immunogenicity for at least 3 years when stored at 2–8 °C. Surprisingly, even when the cold chain conditions were broken by exposing the VLPs to 37 °C or 25 °C for weeks, the VLPs’ structural stability was retained . StoringAlthough the experimental findings described above highlight the temperature stability aspect of the VLPs, one must take into account that each VLP is unique and variations in structural properties are highly plausible. Consequently, directly translating or applying the findings observed from one VLP to draw a general conclusion would be misleading. For example, the FDA-approved Cervarix VLP vaccine underwent substantial downstream processes, which are time-consuming and costly from a manufacturing standpoint, that influenced the structural properties of the VLPs. As most of the experimental VLPs were not subjected to such purification steps to ensure their suitability for clinical use, the stability aspect of FDA-approved VLPs does not apply to those that were not subjected to identical conditions.Giardia lamblia. The cysteine-rich variant-specific surface proteins (VSPs) of G. lamblia not only serve as a proteolytic degradation-resilient tool but also act as TLR4-dependent immunostimulatory molecules. Using this concept, Serradell et al. [G. lamblia VSP components failed to prevent weight loss or elicit 100% survival. This approach was also used for SARS-CoV-2 VLPs to prevent their degradation in the gastrointestinal tract, which successfully induced mucosal immune responses in mice and hamsters when administered through the oral route [Several strategies have been developed to improve the mucosal immune response induced by the VLP vaccines. One such method is developing degradation-resistant VLPs that can endure the highly acidic environmental conditions of the stomach following oral immunization. This can be achieved by exploiting the structural components of gastrointestinal protozoan parasites such as l et al.  demonstral route . BecauseInfluenza, RSV, and SARS-CoV-2, since their initial discovery, have placed a tremendous emphasis on the need for safe and efficacious vaccine development. With the recent advances in biotechnology enabling the construction of VLPs, massive improvements to the field of vaccinology have been met at unprecedented speed, and their development offered a more effective vaccination strategy against emerging respiratory pathogens. Existing evidence from copious amounts of pre-clinical data suggests that VLPs are effective prophylactic tools against these three viruses, and this fueled their further development in clinical trials. While none of the VLP vaccines described here are commercially available, with CoVLP being the sole exception, at least within Canada, we anticipate that VLP-based vaccines for the respiratory RNA viruses covered here will be available for clinical use within a few decades.


To report a case of bilateral anterior intermediate uveitis after recovery from SARS-CoV-2 associated multisystem inflammatory syndrome in children (MIS-C).A 9-year-old male presented with bilateral anterior intermediate uveitis with fluorescein angiography (FA) leakage of the disc and peripheral vasculature 1 month after recovery from MIS-C. He was treated with difluprednate 0.05% in both eyes with resolution of FA leakage, but our patient has required an extended treatment of topical therapy and the need long term immunosuppression.This is a case of uveitis presenting after recent MIS-C related to SARS-CoV-2. Ongoing follow up and monitoring is required, and it is important for the ophthalmologist and rheumatologist to be aware of this rare complication during the current COVID-19 pandemic. Multisystem inflammatory syndrome in children (MIS-C) has emerged as a rare clinical entity in pediatric patients with recent exposure to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Patients can present with a myriad of findings including fever, mucocutaneous changes, cardiac conduction abnormalities, myocardial dysfunction, gastrointestinal abnormalities, and neurological changes with nonspecific laboratory derangements in inflammatory and coagulation pathways. MIS-C is thought to be distinctly different from Kawasaki disease (KD) although overlap in clinical presentation does exist. The American College of Rheumatology diagnostic criteria and consensus guidelines for the diagnosis and management of MIS-C associated with SARS-CoV-2 includes conjunctivitis as a clinical feature . OphthalA 9-year-old male with a past medical history of obesity, asthma, and coronavirus COVID-19) infection one-month prior requiring hospitalization presented with fever, chills, myalgias, right eye conjunctivitis, cracked edematous lips, abdominal pain, macular rash on back and knees, and lower extremity edema. Laboratory evaluation revealed anemia , thrombocytopenia , and elevated c-reactive protein , erythrocyte sedimentation rate , fibrin d-dimer , functional fibrinogen , activated partial thromboplastin time , and prothrombin time . Imaging studies obtained at admission included a normal chest x-ray, a normal echocardiogram, and an abnormal CT of the abdomen that displayed right lower quadrant lymphadenopathy  was performed which revealed disc leakage and peripheral vascular leakage in both eyes (Fig. This is a case of bilateral anterior and intermediate uveitis that was temporally associated with recent MIS-C.Very few ophthalmic complications have been reported in pediatric patients with active or recent COVID-19 infection which include conjunctivitis and uveitis –6. UveitIn adult patients, uveitis has been diagnosed during acute SARS-CoV-2 infection and during disease convalescence. Particularly, in one case a diagnosis of bilateral intermediate and posterior uveitis was made 6 weeks after acute SARS-CoV-2 infection. Oral prednisone therapy was initiated and adequately treated this disease, but this patient flared and was treated with long term immunosuppression with azathioprine .Uveitis is a known manifestation of Kawasaki disease and can be present in 29–83% of patients [


Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mRNA vaccine-induced myocarditis is a rare but well-documented complication in young males. The increased incidence of sudden death among athletes following vaccination has been reported and requires further investigation. Whether the risk of myocarditis, a known major cause of sudden death in young male athletes, also increases after coronavirus disease 2019 (COVID-19) infection is unknown. The severity and implications of these critical adverse effects require a thorough analysis to elucidate their key triggering mechanisms. The present review aimed to evaluate whether there is a justification to hypothesize that catecholamines in a “hypercatecholaminergic” state are the key trigger of SARS-CoV-2 mRNA vaccine-induced myocarditis and related outcomes and whether similar risks are also present following COVID-19 infection.A thorough, structured scoping review of the literature was performed to build the hypothesis through three pillars: detection of myocarditis risk, potential alterations and abnormalities identified after SARS-CoV-2 mRNA vaccination or COVID-19 infection and consequent events, and physiological characteristics of the most affected population. The following terms were searched in indexed and non-indexed peer review articles and recent preprints (<12 months): agent, “SARS-CoV-2” or “COVID-19”; event, “myocarditis” or “sudden death(s)” or “myocarditis+sudden death(s)” or “cardiac event(s)”; underlying cause, “mRNA” or “spike protein” or “infection” or “vaccine”; proposed trigger, “catecholamine(s)” or “adrenaline” or “epinephrine” or “noradrenaline” or “norepinephrine” or “testosterone”; and affected population, “young male(s)” or “athlete(s).” The rationale and data that supported the hypothesis were as follows: SARS-CoV-2 mRNA vaccine-induced myocarditis primarily affected young males, while the risk was not observed following COVID-19 infection; independent autopsies or biopsies of patients who presented post-SARS-CoV-2 mRNA vaccine myocarditis in different geographical regions enabled the conclusion that a primary hypercatecholaminergic state was the key trigger of these events; SARS-CoV-2 mRNA was densely present, and SARS-CoV-2 spike protein was progressively produced in adrenal medulla chromaffin cells, which are responsible for catecholamine production; the dihydroxyphenylalanine decarboxylase enzyme that converts dopamine into noradrenaline was overexpressed in the presence of SARS-CoV-2 mRNA, leading to enhanced noradrenaline activity; catecholamine responses were physiologically higher in young adults and males than in other populations; catecholamine responses and resting catecholamine production were higher in male athletes than in non-athletes; catecholamine responses to stress and its sensitivity were enhanced in the presence of androgens; and catecholamine expressions in young male athletes were already high at baseline, were higher following vaccination, and were higher than those in non-vaccinated athletes.The epidemiological, autopsy, molecular, and physiological findings unanimously and strongly suggest that a hypercatecholaminergic state is the critical trigger of the rare cases of myocarditis due to components from SARS-CoV-2, potentially increasing sudden deaths among elite male athletes. Coronavirus disease 2019 (COVID-19), a multisystemic disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was first detected in Wuhan, China, at the end of 2019. COVID-19 led to the first pandemic of the 21st century, causing more than six million deaths and 800 million cases until June 2022.The peculiarities of SARS-CoV-2 caused a disease characterized by complex pathophysiology that has not been fully elucidated and changes across its variants, leading to widely varying disease presentation and severity. This indicates that COVID-19 depends more on the host (humans) than on the virus itself. This particularity of COVID-19 also implies that the monitoring of COVID-19 effects should be age-, sex-, and comorbidity-specific for a more precise understanding of the risk factors not only for COVID-19 directly related outcomes but also for further complications.As the large variability in presentation, severity, and complications observed in COVID-19 is likely attributed to the specificities of SARS-CoV-2 mRNA and spike protein, it should be expected and therefore presumed that SARS-CoV-2 vaccines of any type, which expose individuals to these proteins, should also be monitored in a characteristic-specific manner.Surveillance of long-term effects of COVID-19 and SARS-CoV-2 vaccinesEfforts to mitigate the COVID-19 pandemic have been tremendous and included multiple public health recommendations and mandates, pharmacological treatments, and vaccine development. Vaccines of different types, including attenuated virus, viral vector, and SARS-CoV-2 mRNA vaccines, were developed at record speed to protect humans against COVID-19 and its outcomes. Despite regional disparities, the massive worldwide vaccination for COVID-19 achieved in <1 year may have contributed to an overall reduction in COVID-19 cases and, to a greater extent, COVID-19 deaths.However, neither the characterization of COVID-19’s long-term effects, including post-COVID-19 or long COVID-19 or increased complications after COVID-19, nor the long-term safety profile and less common adverse effects of SARS-CoV-2 vaccines is well established. Ethically, collective thorough surveillance of complications after COVID-19 and SARS-CoV-2 vaccination is mandatory. Correspondingly, every event chronologically related to COVID-19 infection or SARS-CoV-2 vaccination should be presumably considered as being related until proved otherwise. When the incidence of a certain event is apparently higher after COVID-19 infection or SARS-CoV-2 vaccination within a population of a specific sex and age range when compared to the incidence of this event in the same population before the COVID-19 pandemic or the start of COVID-19 vaccination or to the same population without exposure to SARS-CoV-2 or SARS-CoV-2 vaccines, further investigations must be conducted to fully elucidate the event. Active surveillance and investigations should be equally used for events related to COVID-19 infection and SARS-CoV-2 vaccines non-discriminatorily.Despite insufficient surveillance, some post-SARS-CoV-2 infection and post-SARS-CoV-2 vaccination effects have been identified. An increased number of reports of myocarditis in young males and sudden deaths in male athletes chronologically following SARS-CoV-2 mRNA vaccination raised concern and led to initial investigations regarding the correlation and causality between these events and this specific type of SARS-CoV-2 vaccine. The evidence indicating that cardiac risks are specific to SARS-CoV-2 mRNA vaccines rather than to COVID-19 or post-COVID is compelling, as multiple independent groups and data from different regions demonstrated not only similar findings but also similar patterns that the second SARS-CoV-2 mRNA vaccine dose presents a stronger risk of myocarditis and pericarditis than the first dose and that the young population, particularly males, are at the highest risk. Conversely, despite the overwhelming increase in reports of sudden deaths in male athletes and young males, there remains a lack of more robust literature to support this claim.Myocarditis and sudden death after COVID-19 mRNA vaccinationMyocarditis induced by SARS-CoV-2 mRNA vaccines is an indisputable complication observed particularly in young males -4 as demAmong all population studies that universally detected increased myocarditis risk after SARS-CoV-2 mRNA vaccination, a nationwide fully controlled Israeli dataset identified a strict correlation between both first and second SARS-CoV-2 mRNA vaccine doses and an increase in emergency calls, particularly in those between the ages of 16 and 39 years, after adjustments for confounders . The facNot only were myocarditis risks identified, but a great burden following these cardiac events was also described . Indeed,Although preliminary comparisons between COVID-19 infection and SARS-CoV-2 mRNA vaccines demonstrated similar increased myocarditis risk in athletes and people aged <40 years -14, the Indeed, the alleged similar increase in myocarditis risk following COVID-19 infection and SARS-CoV-2 mRNA vaccines was refuted. While findings of overwhelming increases in symptomatic myocarditis have been extensively demonstrated and reproduced, another strictly controlled Israeli dataset involving a large population study with 196,992 COVID-19 cases and 590,976 controls demonstrated similar myocarditis incidence between people who had been infected with COVID-19 and among non-COVID-19-infected patients .Correspondingly, although an increase in sudden deaths among young people has been reported since the 1990s , the incHowever, this is an anecdotal and empirical observation that has not been confirmed, while numbers are highly underestimated , obscuriCorrelation between myocarditis and sudden deathThe correlations between myocarditis and sudden death vary widely according to the population studied . HoweverHypothesis and objectiveWhile young males and male athletes appear to be at higher risk of cardiac events as observed in a chronologically correlative manner, causality has not been established. The particularities of these populations should be prioritized as potential causes. The two major aspects hypothesized to be specific to these populations are high testosterone and high catecholamine  levels, which alone or combined may experience interference by SARS-CoV-2 components, including the disease (COVID-19) and vaccines. In particular, there appear to be overwhelming chronological coincidences between catecholamine peaks and the incidence of the associated cardiac events. From these observations, it was hypothesized that a “hypercatecholaminergic” state, increased catecholamine levels, and enhanced sensitivity to catecholamines combined with high testosterone levels may mediate SARS-CoV-2 mRNA vaccine-induced myocarditis and related events. In the present article, a scoping review of the emerging literature was performed to substantiate or refute the proposed hypothesis. Ultimately, this article does not aim to discourage or stimulate hesitation regarding SARS-CoV-2 vaccines but to detect and propose explanations for the phenomenon, leading to more effective monitoring and prevention of further events.Materials and methodsAre catecholamines under a hypercatecholaminergic state the key trigger of COVID-19 mRNA vaccine-induced myocarditis and related sudden deaths?While the incidence of sudden deaths among athletes is uncertain, the occurrence of COVID-19 mRNA vaccine-induced clinically detectable myocarditis is unquestionable. The underlying mechanisms of both potentially linked situations deserve further elucidation. For the reasons described in the following paragraphs and through extensive literature research, evaluation was performed on the proposed hypothesis: catecholamines under a hypercatecholaminergic state that includes enhanced catecholamine responses, sensitivity, and action might be the key mechanism for inducing myocarditis and consequent sudden death, particularly in young males and athletes.To build the hypothesis, the following pillars for the hypothesis must be characterized: detection of the risk of the event (myocarditis and related outcomes) (pillar 1) (for detecting the phenomenon), and potential alterations and abnormalities identified after SARS-CoV-2 mRNA vaccination or COVID-19 infection and consequent events (pillar 2) and physiological characteristics specific to the population likely most affected by myocarditis and the related outcomes (pillar 3) (for searching for the etiology of the phenomenon).To characterize each pillar, the following specific questions should be answered. For pillar 1, the questions are as follows: (1) Do SARS-CoV-2 mRNA vaccines lead to increased myocarditis risk? If so, are young males and male athletes at the highest risk for this complication? Is the risk dose-dependent, i.e., do further doses lead to further increments in myocarditis risk? (2) Does this also apply to pericarditis, cardiac events, and sudden deaths? (3) Is the same increased myocarditis risk also observed during or after COVID-19 infection? If so, do the characteristics of this event have similar severity, prognosis, and population affected as the events after SARS-CoV-2 mRNA vaccination?The questions for pillar 2 are as follows: (1) Does any between SARS-CoV-2 mRNA vaccines or COVID-19 infection lead to increased catecholaminergic  activity at any level, including increased secretion from the adrenal medulla and sympathetic ganglions, increased catecholamine receptor sensitivity, or increased response to catecholamine signaling? In summary, do any of them lead to a hypercatecholaminergic state? (2) Has it been demonstrated that any of the specific populations that presented the highest myocarditis risk also presented increased catecholaminergic activity with SARS-CoV-2 mRNA vaccines? (3) Are myocarditis and the related outcomes influenced or induced by a hypercatecholaminergic state?For pillar 3, the questions are as follows: (1) Do young males present increased catecholaminergic activity of any sort compared to older males or to females? (2) Do male athletes present increased catecholaminergic activity of any sort compared to sex- and age-matched non-athletes? (3) Do these two populations of young males and male athletes present higher testosterone levels compared to other populations? (4) If young males, male athletes, or both present both increased catecholaminergic activity and testosterone levels, do these two particularities play a synergistic role leading to further enhancement of the activity of these hormones? In this specific case, do higher testosterone levels lead to further increases in catecholaminergic activity?Once these three pillars are well-characterized, the hypothesis that a hypercatecholaminergic state is likely a key trigger of SARS-CoV-2 mRNA vaccine-induced myocarditis can be confirmed, reinforced, undermined, or refuted.The detection of the phenomenon, i.e., the answers to the questions regarding pillar 1, has been answered in the Introduction section and forms the background of the proposed hypothesis.The answer to pillar 1 is that increased myocarditis risk has been extensively confirmed after SARS-CoV-2 mRNA vaccination, while it is unlikely to be present following COVID-19 infection. The increased myocarditis risk detected in young males was highest (6-30-fold increased risk) as compared to that in unvaccinated age- and sex-matched controls or to myocarditis incidence in the same population before COVID-19 mRNA vaccination.Whether myocarditis risk is even higher among athletes  and whether the incidence of sudden death (or not) following myocarditis also increases after SARS-CoV-2 mRNA vaccination are less clear but deserve consideration for the present hypothesis. Under uncertainties, as the principle of caution should prevail under uncertainties, these events must be considered real risks until demonstrated otherwise.While the questions for pillar 1 were answered in the Introduction and formed the rationale for the proposed hypothesis, the answers to the questions for pillars 2 and 3 constitute the objective of the present analysis, which will be performed in the Results section following the search methods described below.Design and search methodsA scoping review of the existing literature was performed and applied to the hypothesis development process. The corresponding literature in indexed peer-reviewed articles in PubMed (MEDLINE), indexed and non-indexed peer-reviewed articles and preprints on Google Scholar, and recent preprints  in medRxiv, Research Square, and ResearchGate were searched. Expressions regarding the following were searched: agent, “SARS-CoV-2” or “COVID-19”; event, “myocarditis” or “sudden death(s)” or “myocarditis+sudden death(s)” or “cardiac event(s)”; underlying cause, “mRNA” or “spike protein” or “infection” or “vaccine”; proposed trigger, “catecholamine(s)” or “adrenaline” or “epinephrine” or “noradrenaline” or “norepinephrine” or “testosterone”; and affected population, “young male(s)” or “athlete(s).”If the description of the phenomenon potentially linked with SARS-CoV-2 components or COVID-19 was recent, the search was not restricted to published articles. As this is a descriptive review aiming to describe a hypothesis, a systematic review, although structured, was therefore not the objective of the present article. Figure Findings from autopsies of post-COVID-19 mRNA vaccination deathsAutopsies were performed on two adolescents who died from myocarditis three and four days after BNT162b2 vaccination. Both cases were negative for medication or drug misuse. Histologically, the cardiomyocytes presented extensive diffuse contraction band necrosis (CBN) with hypercontracted sarcomeres and mononuclear inflammatory response. These findings contrast those following infarction, in which polymorphonuclear inflammation is observed .The autopsy of a 22-year-old male after sudden death due to myocarditis a few days after the first dose of the BNT162b2 vaccine revealed no inflammatory or cellular response or thrombosis in the ventricular area. Conversely, cardiomyocyte necrosis and scattered single-cell necrosis, degeneration, and adjacent inflammatory infiltrate were noted. The most remarkable characteristic was multiple scattered foci of CBN throughout the myocardium predominantly in the left ventricle, which is the most muscular heart chamber. These findings define catecholamine-induced myocarditis, mixing the early (necrotic and damaged cardiomyocytes) and later (inflammation) stages of injury caused by catecholamines .In both reports, the possibility of any hypersensitivity reaction was excluded as eosinophilic infiltrate was absent. Overall, the injury pattern in all three cases was consistent with stress cardiomyopathy with contraction bands caused by excessive catecholaminergic activity . These histopathological findings are exceedingly similar to the non-rare myocarditis complication of pheochromocytoma, a catecholamine-producing tumor in the adrenal medulla due to abnormal chromaffin cell proliferation -28.Before the specific characteristics of catecholamine-induced myocarditis were searched, two cases from among the first reported cases of myocarditis following SARS-CoV-2 mRNA vaccination demonstrated indirect signals of a hypercatecholaminergic state .The first case was a 45-year-old female who presented acute heart failure due to fulminant myocarditis 10 days after the first dose of the BNT162b2 vaccine. All other causes that could potentially lead to myocarditis, including COVID-19, coronary artery disease, other infections, and other inflammatory or autoimmune diseases, were excluded. The standard therapy for congestive heart failure  led to an unexpectedly sharp rise in the left ventricle ejection fraction within seven days of therapy from 15%-20% to 60%, a faster recovery than expected. The fast recovery may solely be explained if the underlying triggering cause of the myocarditis had been obstructed. In the present case, the direct antagonist actions of a potential hyperadrenergic state that may have led to the myocarditis state with a beta-adrenergic blocker (metoprolol) may have justified the prompt recovery, although further actions of the angiotensin-converting enzyme inhibitor (ACEi) (lisinopril) and mineralocorticoid antagonist (spironolactone) may have exerted synergistic protective effects on ACE expression and balance between its receptors.The second case was a 42-year-old male who died after cardiac shock caused by myocarditis, which clinically manifested as fever, tachycardia, dyspnea, and chest pain, that started two weeks after a second dose of the mRNA-1273 vaccine. Other causes of myocarditis and death, including COVID-19, other viral infections, and obstructive coronary artery disease, were excluded. Similar to the first case, this fatal event was largely attributed to a hypercatecholaminergic state, which was unlikely to be secondary to infections or any type of inflammation-induced diseases as these conditions had been excluded. This reinforced the hypothesis of a primary hypercatecholaminergic state as a trigger of this event.The first report of severe acute myocarditis after the third dose of the SARS-CoV-2 mRNA vaccine was in a 43-year-old female who presented rapid monomorphic ventricular tachycardia (VT) potentially caused by a catecholaminergic storm. For myocarditis and VT, diagnoses of acute coronary disease, COVID-19, other viral or bacterial infections, autoimmune disorders, or any other disease known to cause myocarditis and VT were excluded . DespiteIn all three cases, CD3+ T lymphocytes and CD20+ B lymphocytes were highly present, while macrophages, eosinophils, and other immune cells were almost absent, indicating a lymphocyte-specific induced inflammatory state. These findings supported the hypothesis that all three cases may have been triggered by a hypercatecholaminergic state, as adrenaline and noradrenaline tend to activate lymphocytes while inhibiting monocytes, macrophages, and eosinophils ,32.Unlike cases of post-SARS-CoV-2 mRNA vaccine myocarditis, the autopsies from deaths due to cardiovascular events after COVID-19 infection and other types of SARS-CoV-2 vaccine did not demonstrate contraction bands in the cardiomyocytes or any other indication of damage caused by excessive catecholaminergic activity in any tissue , demonstThe bridge between myocarditis and sudden death after COVID-19 mRNA vaccination: a hyperadrenergic stateAutopsies have demonstrated that catecholamines triggered myocarditis following COVID-19 mRNA vaccination. The bridge connecting myocarditis and sudden death is found in the chronic hyperadrenergic state, a plausible and demonstrated cause -23. ExceThe adrenal glands have been repeatedly demonstrated to be a major site of SARS-CoV-2 mRNA accumulation and SARS-CoV-2 spike protein production, indicating that both the adrenal cortex and medulla were affected. A report evaluating spike protein production after COVID-19 mRNA vaccination determined that the adrenal glands were one of the highest SARS-CoV-2 spike protein-producing tissues, demonstrating that the spike protein production in these glands increased with time . FurtherDespite the lack of a direct comparison, post-COVID-19 autopsies demonstrated that while SARS-CoV-2 mRNA was detected diffusely, including in the adrenal glands , its conThat high SARS-CoV-2 mRNA concentration and corresponding abnormalities in the chromaffin cells that could lead to a catecholamine storm was not the only demonstrated finding. The enzyme dihydroxyphenylalanine (DOPA) decarboxylase converts DOPA into dopamine, the precursor of noradrenaline (through dopamine-beta-hydroxylase) and adrenaline ). DOPA decarboxylase is overexpressed in the presence of SARS-CoV-2 mRNA, a phenomenon not restricted to the adrenal glands. Such overexpression does not occur with other viruses, such as influenza. Naturally, an enhanced diffused conversion from dopamine to noradrenaline occurs locally in the tissues, disproportionately increasing their exposure to catecholamines compared to their serum levels. In addition to the potentially enhanced catecholamine production and release, and beta-2 adrenergic receptor hypersensitivity in tissue, disproportionally high adrenaline levels might be present .Physiological differences in catecholamine metabolism according to age, sex, and activity: do young males and athletes have the highest hyperadrenergic activity?Age, sex, and athletic-level physical activity present pronounced differences in the physiology of catecholamine metabolism. Athletes, particularly male athletes, had significantly higher accumulated levels of active catecholamines, even at rest, compared to non-athletes. This observation was based on measuring 12-hour nocturnal urinary catecholamines, which refers to the accumulated release of these hormones throughout the night. While athletes had higher catecholamine levels than sex-, age-, and comorbidity-matched non-athletes, the catecholamine metabolite metanephrine remained unchanged, suggesting unaltered catecholamine clearance that led to a chronic physiological increase in exposure -43.While athletes present higher catecholamine release and responsiveness than non-athletes, virtually, all people analyzed in these studies were aged <40 years, i.e., age was not a major aspect considered in these analyses. Older adults tend to present lower catecholamine activity than young people. A significant age-related decrease in noradrenaline expression and uptake was observed in rats . The decIt is well-established that males present higher catecholamine responses to various stress types than females -50. MoreAlthough the association between sex and the age-related decrease in catecholamine activity was not reported, the age-related and sex-specific catecholamine responses and release might reflect an important interplay between catecholamines and androgens. Catecholamine responses to stress and adrenergic receptor sensitivity are enhanced in the presence of androgens ,53. ThisDysfunctional, exacerbated catecholamine metabolism in young males and athletes after COVID-19 mRNA vaccinationAlready physiologically exposed to high catecholamine levels, athletes experience additional exposure after COVID-19 mRNA vaccination. Although underestimated, recently vaccinated athletes presented significantly higher noradrenaline production in response to graded exercise than before vaccination (p < 0.01). The researchers also compared participants vaccinated with the Pfizer mRNA vaccine and non-vaccinated participants and demonstrated higher noradrenaline production ) and heart rate (p = 0.006 at 70% VO2max). All participants underwent a similar graded exercise program controlled through respiratory parameters .Myocarditis and sudden death are highly specific to young males, particularly male athletes, the population with the highest catecholamine exposure. The underlying cause of these two severe outcomes is a common hyperadrenergic state, universally demonstrated through autopsies that concluded adrenaline-induced myocarditis. Therefore, the plausibility of the hypothesis that catecholamines are the key to the occurrence of myocarditis and sudden death after COVID-19 mRNA vaccinations is considerable and is most likely but requires molecular confirmation.Further hypothesis-supporting dataThe physiological differences in catecholamine responses and the dysfunctional changes in catecholamine production and action after COVID-19 mRNA vaccination strongly support the proposed hypothesis.Local paracrine-acting catecholamine release in response to stress in various tissues is directly related to the adrenal noradrenaline output level. This means that the already physiologically high catecholamine responses observed in young male athletes undergo additional enhancements after COVID-19 mRNA vaccination. These paracrine effects might become even more pronounced upon analysis of the tissue catecholamine concentration and action in various sites, particularly the vessels and muscles, including the cardiomyocytes .A retrospective analysis demonstrated that the use of alpha-1 adrenergic receptor antagonists reduced COVID-19 in-hospital mortality by 77% (odds ratio (OR): 0.23; 95% CI: 0.03-0.94; p = 0.028) , while bThese findings demonstrate the pro-inflammatory effects, harm, and consequent outcomes caused by the excessive catecholaminergic state due to SARS-CoV-2 mRNA and/or spike protein , therebyConversely, the cause of sudden deaths among athletes was largely attributed to ventricular tachycardia following a hypercatecholaminergic state, which may have also induced concurrent myocarditis that could together lead to VT ,62. BothFigure DiscussionSynthesizing Epidemiological, Anatomopathological, Molecular, and Physiological Findings to Propose a Hypothesis of Catecholamines as the Key Trigger of SARS-CoV-2 mRNA Vaccination-Induced Myocarditis and Sudden DeathAltogether, the evidence included the following: the epidemiological findings of COVID-19 mRNA vaccine-induced myocarditis and the potential increase in sudden deaths among young males, particularly athletes; anatomopathological findings during autopsies of myocardial tissue that demonstrated a clear state of catecholamine-triggered myocarditis in all cases; the notable presence of SARS-CoV-2 mRNA and enhanced SARS-CoV-2 spike protein production in adrenal medulla chromaffin cells; the overexpression of the DOPA decarboxylase enzyme in the presence of SARS-CoV-2 mRNA, leading to enhanced conversion of dopamine into noradrenaline; higher physiological catecholamine metabolism in younger people compared to older people, males more than females reinforced by the positive catecholamine response and sensitivity in the presence of androgens, and athletes more than non-athletes where the former is likely the most affected population; and more enhanced catecholamine response in vaccinated athletes than non-vaccinated or pre-vaccinated athletes. All this evidence was fully concordant, which supported the proposed hypothesis that catecholamines are a key player in the SARS-CoV-2 mRNA vaccine-induced myocarditis and the consequent apparent increase in sudden deaths.It is unlikely that the enhanced catecholamine release, response, receptor sensitivity, and overall activity acted alone to provoke the vaccine-induced, catecholamine-triggered myocardial complications. The catecholamines possibly acted synergistically with other dysfunctions, including abnormal immunological and inflammatory responses, as they alone may cause myocarditis only during extreme catecholamine exposure.It remains unclear whether the proteins transcribed by SARS-CoV-2 mRNA or SARS-CoV-2 spike protein or both trigger the hypercatecholaminergic state that eventually causes myocarditis after SARS-CoV-2 mRNA vaccination. However, this should be explored in further study after the proposed hypothesis has been confirmed.The epidemiological findings of SARS-CoV-2 mRNA vaccine-induced myocarditis, which is overrepresented in young males, and the preliminary reports of an increase in sudden deaths, particularly in athletes, while absent after COVID-19 infection present highly concordant molecular justifications for the physiological differences in anatomopathological findings and catecholamine activity, which is more intense in active young males. We may conclude that supported by biological, clinical, and epidemiological findings, enhanced catecholamine activity or a hypercatecholaminergic state provides sufficient evidence for the highly plausible catecholamine theory of SARS-CoV-2 mRNA or spike protein-mediated myocardial complications to be considered a strong hypothesis.


Enteric viruses, including numerous viruses that initiate infection in enteric canal, are recognized as important agents that cause wide spectrum of illnesses in humans, depending on the virus type. They are mainly transmitted by fecal-oral route with several vector such as contaminated water or food. Infections by enteric viruses, such as noroviruses and rotaviruses, frequently cause widespread acute gastroenteritis, leading to significant health and economic burdens and therefore remain a public health concern. Like other viruses, enteric viruses ‘‘hijack’’ certain host factors  for replication in infected cells, while escaping the host defense system by antagonizing host anti-viral factors. Identification(s) of these factors is needed to better understand the molecular mechanisms underlying viral replication and pathogenicity, which will aid the development of efficient antiviral strategies. Recently, the advancement of genome-editing technology, especially the clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9 system, has precipitated numerous breakthroughs across the field of virology, including enteric virus research. For instance, unbiased genome-wide screening employing the CRISPR-Cas9 system has successfully identified a number of previously unrecognized host factors associated with infection by clinically relevant enteric viruses. In this review, we briefly introduce the common techniques of the CRISPR-Cas9 system applied to virological studies and discuss the major findings using this system for studying enteric virus infection. Acute gastroenteritis (AGE) is a disease with symptoms including vomiting, watery diarrhea, stomach pain and dehydration, and is frequently caused by intestinal infection with pathogenic bacteria, viruses, or parasites . Among tSimilar to other viruses, enteric viruses rely on their hosts to successfully multiply in infected cells. Characterization of viral-host interactions is necessary to gain a clear view of the infection and replication mechanisms, which will contribute to developing host-directed drugs against pathogenic viruses. Genome-wide genetic screening is one of the most powerful and rapid tools to uncover new insights into the viral lifecycle through a comprehensive search for host factors associated with viral infection . RecentlStreptococcus pyogenes Cas9) is located upstream of the target nucleotides, which grants specific cleavage of non-self DNA  activation system . dCas isUnbiased genome-wide genetic screening is one of the gold standard methods to comprehensively identify host factors that restrict or promote viral infection . There aThe typical experimental flow of a genome-wide CRISPR-Cas9 screen is shown in The cell type used for screening can be selected depending on the experimental design and/or available resources . For insIn the following sections, we summarize important findings pertaining to each enteric virus infection, mainly focusing on insights obtained from genome-wide CRISPR-Cas9 genetic screens.Norovirus  and contains a positive-sense, single-stranded RNA genome , which belongs to the same genus as HuNoV, has been used as a surrogate virus to understand the molecular mechanism underlying HuNoV infection. MNV can grow robustly in the RAW264.7 murine macrophage cell line with a cytopathic effect. Using this MNV-culture system, unbiased genome-wide CRISPR-Cas9 knockout screens successfully identified CD300lf and CD300ld as functional entry receptors for MNV  and unbiased genome wide screens utilizing the CRISPR-Cas9 system should be highly encouraged to gain further insights regarding the HuNoV infection mechanism.Recently, several successive HuNoV cultivation systems have been developed , one of Rotavirus (family Reoviridae) and is a non-enveloped RNA virus whose genome consists of 11 segmented double-stranded RNAs. Human rotavirus (HRV) primarily infects children under 5 years of age and often induces severe and dehydrating gastroenteritis (® and Rotarix®) were introduced globally over a decade ago, exhibiting high efficacy in preventing rotavirus-related diseases. However, HRV-associated gastroenteritis still leads to >200,000 deaths annually, mostly in low-income countries, possibly because of less availability of rotavirus vaccines and dehydration therapy and lower efficacy of vaccines than those in high-income countries , which grow robustly in transformed mammalian cell lines, including monkey cell lines  and human intestinal epithelial cell lines . Previous genome wide siRNA screens have identified multiple host factors that regulate rotavirus infection (nfection . For exanfection . Recentlnfection . The autnfection . Since tEnteroviruses (EVs) belong to the family Picornaviridae and are a highly diverse group of positive-sense, single-stranded RNA viruses, including many human pathogens such as poliovirus, EV-A71, EV-D68 and rhinovirus. EVs spread through the fecal-oral or respiratory routes and cause a wide variety of diseases, including the common cold, poliomyelitis, hand, foot and mouth disease (HFMD), epidemic pleurodynia, myocarditis, herpangina, encephalitis or acute flaccid paralysis (AFP), depending on the virus type .et al. identified the actin histidine methyltransferase SET domain containing 3 (SETD3) as a novel host factor that controls several enteroviruses, including rhinovirus, EV-D68 and EV-A71  protein was originally reported to interact with EV 3A protein, which recruits PI4KB into viral replication organelles in favor of EV replication . With anvitro human intestinal culture cells and intestinal organoids (Coronaviruses (CoVs), which belong to the genus Coronavirus (family of Coronaviridae) are positive-sense, non-segmented RNA viruses possessing a large genome (approximately 30 kb) . A totalrganoids .In light of the ongoing coronavirus disease 2019 (COVID-19) pandemic, intensive research efforts are currently underway worldwide to understand SARS-CoV-2 pathogenicity and discover new targets for host-directed drugs. CRISPR-Cas9 technology has been widely used to determine viral-host interactions. Indeed, to our knowledge, research outcomes utilizing genome-wide CRISPR-Cas9 knockout screens have already been published by six independent groups since the emergence of COVID-19 . As expeIn addition, Goujon et al., carried out dual genome-wide CRISPR screens (knockout and activation) using the human lung epithelial cell line Calu-3 and identified host factors regulating SARS-CoV-2 infection . It shouThe development of the CRISPR-Cas9 system has revolutionized medical research. In terms of enteric virus research, the CRISPR-Cas9 system has contributed to expanding our understanding of the molecular mechanisms underlying viral infections. In particular, CRISPR-Cas9 knockout/activation screens have led to discovering numerous functional needles in a mammalian genome haystack, including CD300lf and CD300ld (entry receptors for MNV), STAG2 (pro-rotavirus factor), SETD3 , and HMGB1 and RAB7A .Given the accuracy of CRISPR-Cas9 resulting in complete targeted gene knockout, as compared to RNAi with incomplete knockdown, reassessment of RNAi experiments using CRISPR-Cas9 gene knockout may be warranted. This is especially true for gene(s) whose phenotypes have been argued owing to discrepancies between published studies. By contrast, this feature of the CRISPR-Cas9 system is unfavorable when investigating certain gene(s) whose functions are indispensable for cell growth and/or survival, because it is difficult to establish cells lacking such genes. In this case, gene knockdown techniques such as RNAi (siRNA or shRNA) and CRISPR interference (CRISPRi) system, which we mention below, are useful for studying the effect(s) of such essential genes on viral infection.In addition to CRISPR knockout and activation methods, which we introduce in this review, various other application tools are currently available . For ins


Viral-host protein protein interaction (PPI) analysis is essential to decode the molecular mechanism of viral pathogen and host immunity processes which eventually help to control viral diseases and optimize therapeutics. The state-of-the-art viral-host PPI predictor leverages unsupervised embedding learning technique (doc2vec) to generate statistical representations of viral-host protein sequences and a Random Forest classifier for interaction prediction. However, doc2vec approach generates the statistical representations of viral-host protein sequences by merely modelling the local context of residues which only partially captures residue semantics. The paper in hand proposes a novel technique for generating better statistical representations of viral and host protein sequences based on the infusion of comprehensive local and global contextual information of the residues. While local residue context aware encoding captures semantic relatedness and short range dependencies of residues. Global residue context aware encoding captures comprehensive long-range residues dependencies, positional invariance of residues, and unique residue combination distribution important for interaction prediction. Using concatenated rich statistical representations of viral and host protein sequences, a robust machine learning framework “LGCA-VHPPI” is developed which makes use of a deep forest model to effectively model complex non-linearity of viral-host PPI sequences. An in-depth performance comparison of the proposed LGCA-VHPPI framework with existing diverse sequence encoding schemes based viral-host PPI predictors reveals that LGCA-VHPPI outperforms state-of-the-art predictor by 6%, 2%, and 2% in terms of matthews correlation coefficient over 3 different benchmark viral-host PPI prediction datasets. Viral pathogens are causing millions of deaths every year around the world . To dateInitially, physical contacts between viral proteins and host cell proteins were identified by high-throughput wet experimental approaches such as yeast two-hybrid (Y2H), Tandem Affinity Purification (TAP), mass spectroscopy (MS) –8. HowevTo accurately discriminate interactive viral-host protein sequence pairs from non-interactive ones, existing viral-host PPI prediction approaches have utilized a variety of genetic, structural, and biochemical features –21. BaseCritical analysis of pre-known network based viral-host PPI prediction approaches reveals that expression profiles based networks, motif-domain interaction networks are known for a very few organisms, and even these limited resources need periodic updates to match the volume and velocity of Proteomics data . FurtherTo date, several purely raw sequence based computational approaches have been developed –17. As mCui et al.  transforFurthermore, Kim et al.  generateIn a nutshell, the prime focus of every new viral-host PPI predictor has been to learn optimal statistical representations of viral-host protein sequences. Among various statistical representations learning approaches, residue physicochemical properties based viral-host protein sequence representation learning schemes mark better performance than trivial residue frequency based approaches. However, these approaches neglect the relationships among residue segments as a function of context of entire viral-host protein sequences. In the marathon of generating the most effective representation of viral-host protein sequences, following the success of neural residue embeddings in a wide spectrum of Natural Language Processing  and BioiThe paper in hand presents a unique way of generating rich statistical representations of viral-host protein sequences by fusing comprehensive local and global residue contextual information. In local residue context aware sequence encoding, we leverage physico-chemical properties to reduce viral-host protein sequences and categorize the residues present in reduced sequences into 6 different classes according to residue properties given by shannon entropy. statistical representations of viral-host protein sequences are generated through the assignment of residues to these respective classes. Local residue context aware encoding extracts short range dependencies of residues as well as residue semantic relatedness. Whereas, to capture long range dependencies and positional invariance of residues, in global residue context aware encoding, we compute composition and transition of viral-host protein sequences. Finally, to generate comprehensive statistical representations of viral-host protein sequences by capturing diverse types of information, we fuse the features extracted by local residue context aware encoding with the features extracted by global residue context aware encoding. Using optimized concatenated viral and host protein sequences representations, a robust machine learning framework LGCA-VHPPI based on deep forest model is developed which extracts correlation of features important to discriminate interactive viral-host protein pairs from non-interactive protein pairs, generalizeability of which does not affect much from complex data non-linearity, noise, and size of the training set.To illustrate the effectiveness of proposed comprehensive local-global residue context aware viral-host protein sequence representation learning scheme based deep forest model, a detailed performance assessment is performed. Over 3 different benchmark viral-host PPI prediction datasets, local-global residue context aware viral-host protein sequence encoding scheme generate most comprehensive yet discrminative representation, outperforming only local residue context aware sequence encoding and global residue context aware sequence encoding respectively by a decent margin. Furthermore, optimized viral-host protein sequence representation assists the deep forest model to surpass the performance of various predictive approaches, outperforming the state-of-the-art doc2vec and Random Forest classifier based approach by 6%, 2%, and 2% in terms of matthews correlation coefficient over 3 different benchmark viral-host PPI prediction datasets.This section discusses proposed viral-host PPI prediction methodology, benchmark datasets and evaluation metrics used to assess the performance of proposed methodology.To determine the interactions among viral and host proteins, two different kinds of paradigms have been used in the literature to generate statistical representations of viral-host protein sequences , 14, 28.The workflow of proposed LGCA-VHPPI predictor is demonstrated in Proposed Local-Global Residue Context Aware Encoding (LGCAE) scheme is the fusion of 2 different modules 1) Local Residue Context Aware Sequence Encoding (LCAE) and 2) Global Residue Context Aware Sequence Encoding (GCAE), paradigms of which are explained in following sub-sections.Local residue context aware encoding generation of viral-host protein sequences. Using the collection of viral-host protein sequences, local residue context aware encoder “LCAE” computes a dictionary D = {A,R,N,D,C,E,Q,G,H,I,L,K,M,F,P,S,T,W,Y,V} containing 20 unique amino acids. We reduce the distribution of 20 unique amino acids in the viral-host protein sequences to 6 unique classes of amino acids using physico-chemical properties of amino acids such as polarity and hydrophobicity. Considering Shannon entropy of amino acids properties [operties , rather operties ), which S = S1…‥Sn of length n where Sq represents a particular residue, an initial level numerical representation is generated by iteratively mapping the sequence S to every group vi expressed in terms of 4 unique letters  and replacing 4 unique letters with corresponding ASCII values. To optimize initial level numerical representation of viral-host protein sequences generated for each group vi, following the success of transformer based approaches to capture positional information of residues for diverse Natural Language Processing and Bioinformatics tasks [S represented as Bn, On,Jn, Un as well their count in initial j entries  of sequence where j is iteratively updated until it matches the length n of sequence. Using total occurrences of 4 unique letters  and their iteratively increasing counts ), we capture alteration in positional bits of all 4 unique letters in such a manner that odd and even position values fall in range of cosine and sine functions, mathematical expressions of which are given in Eqs Furthermore, to better describe the process to generate statistical representations of viral-host protein sequences using 20 different patterns, Let us consider a viral host protein sequence cs tasks , 32, we XSq(vi) and YSq(vi) obtained from Eqs Using XSq(vi), ∑YSq(vi), ∑A(vi), and ∑B(vi) denote the sum of floating point values present in respective collections (XSq(vi), YSq(vi), A(vi), and B(vi)).In Eqs Then, LCAE vector with respect to each group can be computed by concatenating 4 normalized vectors .LCAEG1=As we have 20 different patterns, so comprehensive semantic relatedness and short range residue dependencies aware (LCAE) viral-host protein sequences representations can be generated by combining the representation of 20 different patterns . For eacGlobal residue context aware encoding generation of viral-host protein sequences. Global residue context aware encoding (GCAE) captures comprehensive composition and transition information of residues. First, using the collection of viral and host protein sequences, a dictionary D = A,R,N,D,C,E,Q,G, H,I,L,K,M,F,P,S,T,W,Y,V containing 20 unique amino acids is computed. Then for a given viral or host protein sequence S = S1,….,Sn; of length n where Si represents a particular amino acid present in dictionary D, GCAE generates a sparse 20×n matrix A where 20 unique amino acids act as row indices and sequence residues Sn act as column indices. Sparse matrix A looks like:A is distributed with the values of 0 and 1 as every cell represented as ai,j) matches with amino acid present in column index S(j) and 0 otherwise. As basic working principal of global context aware encoder is to capture composition and transition of amino acids in viral-host protein sequences. Here in the matrix, length of each amino acid is equal to the length of particular viral or host protein sequence. Hence, instead of finding the composition and transition of amino acid by taking the full rows of the matrix, we divide the rows into L number of sub-rows/sub-regions. Depending upon the size of input viral or host protein sequence and value of L, it is highly likely that one of many sub-regions is shorter in length due to low leftover amino acids in the input sequence. For example, for a sequence containing 25 amino acids, if we select L = 2, then two sub-regions will have the different number of amino acids such as 13, and 12 respectively. However, GCAE operates on same size sub-regions. Hence, to generate same size sub-regions, pre-processing strategy will first add one non-amino acid letter B at the end of input sequence and then divides the sequence into 2 sub-regions where each sub-region will have 13 amino acids. In other words, for a given viral or host protein sequence, before the generation of L number of sub-regions, pre-processing strategy extends the length of given sequence using the copy padding trick where it adds a non amino-acid letter (e.g B) at the end of input sequence as many times as it makes the generation of same size L number of sub-regions possible. After generating same size sub-regions, we compute composition and transition with respect to each sub-region.Sparse matrix The composition computes the frequency of ‘1”, ‘11”, and ‘111” in each row of sparse matrix to capture the proportion of various residues within sequence and their most dominant contexts.Whereas, transition computes the frequency of ‘1” followed by ‘0” and ‘0” followed by ‘1” in each row of the sparse matrix to capture the dominant change in the context of the residue.Because, transition computes two different trends for each sub-vector ∈ L,, hence dimensions of transition vector can be computed as:By concatenating composition and transition vectors, GCAE viral-host protein sequence vector is generated. To better illustrate the working paradigm of global residue context aware encoding, a hypothetical example is demonstrated in Consider a hypothetical viral protein sequence containing 40 residues. To generate statistical representations of this viral protein sequence, GCAE first generates a 2-dimensional matrix of size amino acid: 20 ×size of sequence (40). In this matrix, 20 amino acids act as rows indices and 40 amino acids present in sequence as column indices and each cell of every row gets the value of 1 or 0 depending on the match of row index with column index. This sequence is divided into four sub-regions of 10 amino acids by taking sub-region size L = 4 where GCAE computes composition and transition of residues with respect to every sub-regions across entire rows of sparse matrix. To better illustrate the working paradigm of GCAE, Fusion of local and global residue context aware sequence encoders. Local-Global context aware sequence encoding is generated by fusing local sequence vector produced by LCAE with global sequence vector produced by GCAELocal-Global context aware sequence encoding is generated by fusing 40-dimensional local sequence vector with 400 dimensional global sequence vector which ensures that statistical representations of viral or host protein sequences contain comprehensive short and long range positional as well as semantic information of residues important to discriminate interactive viral-host protein sequence pairs from non-interactive viral-host protein sequence pairs.To distinguish interactive viral-host protein sequences from non-interactive ones, we use a deep forest model. Deep forest model comprises of a sequence of random forests where each random forest is trained over sequences statistical vectors440-dimensional sequence vectors produced by proposed LGCAE scheme and yields a 2-dimensional probability class vector. Contrary to deep neural networks, deep forest model is extremely effective in learning hyper-level representation with lowest cost and has shown great promise in multifarious bioinformatics tasks . Deep foFurthermore, a number of hyperparameters can be tuned in a deep forest model such as decision trees estimators, maximum depth of individual decision tree estimator, node splitting criteria, minimum samples used to split on at the internal node of decision tree estimators, amount of random features used at every node for splitting, maximum leaf nodes, and size of bootstrapped dataset used to train every decision tree , 35. PreIn order to evaluate the integrity of proposed viral-host PPI predictor “LGCA-VHPPI”, we have collected 3 different benchmark datasets from 3 different research studies , 14, 28,Barman et al.  preparedAnother benchmark viral-host PPI dataset (DeNovo dataset) was prepared by Fatma et al.  using ViThird benchmark viral-host PPI dataset was prepared by Yang et al. . They utFollowing the evaluation criteria of different researchers used to evaluate their proposed viral-host PPI prediction methodologies, we evaluate the performance and generalizeability of proposed viral-host PPI prediction methodology LGCA-VHPPI in terms of 8 different evaluation metrics , mathema+ refers to the count of false and true positives, O- represents the count of false and true negatives, true positives are represented by Here in The proposed local-global residue context aware viral-host protein sequence representation learning scheme and deep forest are implemented using python based open source libraries .To perform a fair performance comparison of proposed LGCA-VHPPI predictor with existing predictors, following Barman et al. work , we haveThis section illustrates the performance of global context aware encoder with different number of sub-regions. It illustrates the performance values and generalizability achieved by deep forest classifier under the hood of three different viral-host protein sequence representation learning schemes solely based on the local distribution of residues, global distribution of residues, and fused local-global distribution of residues using three different benchmark datasets. Furthermore, it performs a fair performance comparison of proposed local-global residue context aware sequence encoding and deep forest based methodology LGCA-VHPPI with existing viral-host PPI predictors namely Barman et al.  approachL related to number of sub-regions in global context aware encoding (GCAE) approach, we take 80% sequences of Barman dataset [L from 4 to 40 to assess the impact of different number of sub-regions on the performance of GCAE produced using deep forest classifier for the task of viral-host PPI prediction. As shown by the L), and on Yang et al dataset, GCAE performance remains at 94% until 8 sub-regions and drops by only 1% afterwards. This indicates that parameter L related to different number of sub-regions does not significantly influence the performance of GCAE across all three benchmark datasets, hence, we have divided viral and host protein sequences in 6 sub-regions to generate GCAE based representations across all three datasets.To find the optimal value of parameter  dataset , and com dataset  and Yang dataset  datasetsFurthermore, to reveal the true generalization potential of deep forest across 3 different benchmark datasets under the hood of 3 statistical representations learning schemes, performance of LCAE, GCAE, and LCGAE is compared using AU-ROC and AU-PRC, shown in Figs In a nutshell, the main reason for LGCAE better performance and generalizeability is the context coverage which is highest in LGCAE as compared to LCAE and GCAE. LGCAE fuses different contextual granularity of sequence residues to capture generic yet discriminative distribution of residues which leads to better generalizeability across different viral species by ensuring deep forest model does not over-specialize certain regions of viral-host protein sequences. Furthermore, despite very different sequence to label distribution, proposed LGCAE based deep forest approach manages to produce promising accuracy, AU-ROC and AU-PRC across all 3 different benchmark datasets, revealing that the performance of proposed approach is not influenced much by the size of training data as well as size of positive or negative class. A promising performance and generalizability across multiple datasets makes the proposed local-global context aware encoding based viral-host PPI predictor LGCA-VHPPI an appropriate candidate for other pathogens-human PPI prediction. Like viral-host PPI prediction task, a robust computational approach to accurately determine the interaction of other pathogens such as protist or bacteria (e.g Haemophilus influenza) with human protein is mainly comprised of two different modules 1) Effective statistical representations Generation 2) Interaction Prediction. This paper provides a unique way to generate an effective statistical representations of viral-host protein sequences by modeling the local and global context of residues, using which even a simple deep forest classifier manages to extract most discriminative features which help the classifier to outperform state-of-the-art viral-host PPI prediction approaches. Hence, we consider this unique way can be used to generate an effective statistical representations of bacteria-human or prostist-human proteins sequences which can be passed to any machine or deep learning classifier for accurate pathogen-human PPI prediction.It is evident from the Viral-host PPI prediction only facilitates whether particular viral-host protein pairs are interactive or non-interactive. The main goal of viral-host PPI pathway analysis is to determine which viral proteins interact with which host proteins. Beside providing a robust viral-host PPI predictor, we also facilitate viral-host PPI pathway analysis using proposed predictor which utilizes the interaction information of viral and host proteins. To accomplish viral-host PPI pathway analysis, we take the model trained on Denovo training set and assess the interaction pathway analysis power of trained model on a randomly chosen virus protein and human protein from test set of Denovo dataset.To illustrate better, interaction pathways of randomly selected viral protein called Nipah virus  and arbitrarily selected human protein called Tubulin beta-4B (Acronym: TBB4B identifier: P68371)are shown in Proposed model accurately predicts 29 positive interactions of Nipah virus and 11 positive interactions of Tubulin beta-4B human proteins. A similar performance trend is shown by proposed model for various other viruses and human proteins which is why it manages to achieve promising performance in terms of different evaluation metrics as compared to state-of-the-art viral-host PPI predictors. This also reveals the supreme potential of proposed model to perform comprehensive interaction pathway analysis of multiple viral species with respect to human proteins and vice versa.https://sds_genetic_analysis.opendfki.de/HVI/. This web server can be used to determine interactions among viral and host proteins merely using raw sequences related to diverse viral species. It can also be used to complement experimental approaches because it can validate experimentally detected viral-host PPIs. Unlike existing Genomics and Proteomics sequence analysis web servers, it can be used to train and optimize machine learning model from scratch on account of proteins belonging to new viral species and perform prediction on novel sequences belonging to existing or new virus species.To facilitate Genomics and Proteomics researchers and practitioners, we have developed an interactive and user-friendly LGCA-VHPPI web server available at A comprehensive performance analysis of proposed viral-host PPI predictor leads to conclude that generating statistical representations of viral-host protein sequences by fusing comprehensive local and global residue contextual information proves really effective to largely raise the generalizeability of deep forest classifier across a variety of species. While local residue context aware encoder assigns higher weights to those residues which share similar context while generating statistical representations of viral-host protein sequences, global residue context aware encoder generates statistical representations of viral-host protein sequences by modelling long range dependencies and positional invariance of residues. Using optimized sequence representation based on the integration of local and global context aware encoders, proposed viral-host PPI predictor(LGCA-VHPPI) manages to extract crucial residue correlations and hidden patterns important for accurate interaction prediction. A compelling future line of current work would be to investigate the performance impact of diverse neural strategies (e.g attention) at the level of sequence encoding and interaction prediction.S1 Data(XLSX)Click here for additional data file.S2 Data(BST)Click here for additional data file.