Silent spread of highly pathogenic Avian Influenza H5N1 virus amongst vaccinated commercial layers

• Published in: Research in veterinary science Vol. 97; no. 3; pp. 637 - 641
• Main Authors: Poetri, Okti Nadia, Van Boven, Michiel, Claassen, Ivo, Koch, Guus, Wibawan, I.Wayan, Stegeman, Arjan, Van den Broek, Jan, Bouma, Annemarie
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-12-2014; Elsevier Limited
• Subjects: Animal vaccines; Animals; Avian influenza; Avian influenza virus; Birds; Chickens; evolution; Experiments; H5N1; Hemagglutination Inhibition Tests - veterinary; Immunization; Infections; Influenza A Virus, H5N1 Subtype - genetics; Influenza A Virus, H5N1 Subtype - immunology; Influenza in Birds - prevention & control; Influenza in Birds - transmission; Influenza Vaccines - administration & dosage; Influenza Vaccines - immunology; Layer; poultry; Transmission; Vaccination; Vaccination - veterinary; Vaccines, Inactivated - administration & dosage; Vaccines, Inactivated - immunology; Veterinary medicine; Virus Shedding; Avian influenza; H5N1; Layer; Vaccination; Transmission
• ISSN: 0034-5288; 1532-2661
• DOI: 10.1016/j.rvsc.2014.09.013

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.