Molecular epidemiology of ascariasis: a global perspective on the transmission dynamics of Ascaris in people and pigs.
BACKGROUND
The roundworm Ascaris lumbricoides infects 0.8 billion people worldwide, and Ascaris suum infects innumerable pigs across the globe. The extent of natural cross-transmission of Ascaris between pig and human hosts in different geographical settings is unknown, warranting investigation.


METHODS
Adult Ascaris organisms were obtained from humans and pigs in Europe, Africa, Asia, and Latin America. Barcodes were assigned to 536 parasites on the basis of sequence analysis of the mitochondrial cytochrome c oxidase I gene. Genotyping of 410 worms was also conducted using a panel of microsatellite markers. Phylogenetic, population genetic, and Bayesian assignment methods were used for analysis.


RESULTS
There was marked genetic segregation between worms originating from human hosts and those originating from pig hosts. However, human Ascaris infections in Europe were of pig origin, and there was evidence of cross-transmission between humans and pigs in Africa. Significant genetic differentiation exists between parasite populations from different countries, villages, and hosts.


CONCLUSIONS
In conducting an analysis of variation within Ascaris populations from pig and human hosts across the globe, we demonstrate that cross-transmission takes place in developing and developed countries, contingent upon epidemiological potential and local phylogeography. Our results provide novel insights into the transmission dynamics and speciation of Ascaris worms from humans and pigs that are of importance for control programs.
['Betson|Martha|M|', 'Nejsum|Peter|P|', 'Bendall|Richard P|RP|', 'Deb|Rinki M|RM|', 'Stothard|J Russell|JR|']
D000818:Animals D001196:Ascariasis D001200:Ascaris D051545:Cyclooxygenase 1 D018509:DNA, Helminth D006239:Haplotypes D006801:Humans D018895:Microsatellite Repeats D017720:Molecular Epidemiology D013552:Swine D013553:Swine Diseases D015047:Zoonoses
Ascaris barcode microsatellite population genetics giant roundworm neglected tropical disease soil-transmitted helminth zoonosis