Silent spread of highly pathogenic Avian Influenza H5N1 virus amongst vaccinated commercial layers.
The aim of this study was to determine whether a single vaccination of commercial layer type chickens with an inactivated vaccine containing highly pathogenic avian influenza virus strain H5N1 A/chicken/Legok/2003, carried out on the farm, was sufficient to protect against infection with the homologous virus strain. A transmission experiment was carried out with pairs of chicken of which one was inoculated with H5N1 virus and the other contact-exposed. Results showed that the majority of the vaccinated birds developed haemagglutination inhibition (HI) titres below 4log2. No clinical signs were observed in the vaccinated birds and virus shedding was limited. However, nearly all vaccinated birds showed a four-fold or higher increase of HI titres after challenge or contact-exposure, which is an indication of infection. This implies that virus transmission most likely has occurred. This study showed that a single vaccination applied under field conditions induced clinical protection, but was insufficient to induce protection against virus transmission, suggesting that silent spread of virus in vaccinated commercial flocks may occur.
['Poetri|Okti Nadia|ON|', 'Van Boven|Michiel|M|', 'Claassen|Ivo|I|', 'Koch|Guus|G|', 'Wibawan|I Wayan|IW|', 'Stegeman|Arjan|A|', 'Van den Broek|Jan|J|', 'Bouma|Annemarie|A|']
D000818:Animals D002645:Chickens D006385:Hemagglutination Inhibition Tests D053124:Influenza A Virus, H5N1 Subtype D007252:Influenza Vaccines D005585:Influenza in Birds D014611:Vaccination D015164:Vaccines, Inactivated D017201:Virus Shedding
Avian influenza H5N1 Vaccination Layer Transmission