title: Silent spread of highly pathogenic Avian Influenza H5N1 virus amongst vaccinated commercial layers.
abstract: 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.
authors.affiliation: Faculty of Veterinary Medicine, Department of Animal Diseases and Veterinary Public Health, Bogor Agricultural University, Dramaga, Bogor, West Java 16680, Indonesia. Electronic address: diapoetri@gmail.com.
authors.forename: Okti Nadia
authors.initials: ON
authors.lastname: Poetri
authors.affiliation: Centre for Infectious Disease Control, National Institute for Public Health and the Environment, A. van Leeuwenhoeklaan 9, Bilthoven, 3721 MA, Netherlands.
authors.forename: Michiel
authors.initials: M
authors.lastname: Van Boven
authors.affiliation: Central Veterinary Institute, Wageningen University and Research Centre, Part of Wageningen UR, Houtribweg 39, Lelystad 8221 RA, Netherlands.
authors.forename: Ivo
authors.initials: I
authors.lastname: Claassen
authors.affiliation: Central Veterinary Institute, Wageningen University and Research Centre, Part of Wageningen UR, Houtribweg 39, Lelystad 8221 RA, Netherlands.
authors.forename: Guus
authors.initials: G
authors.lastname: Koch
authors.affiliation: Faculty of Veterinary Medicine, Department of Animal Diseases and Veterinary Public Health, Bogor Agricultural University, Dramaga, Bogor, West Java 16680, Indonesia.
authors.forename: I Wayan
authors.initials: IW
authors.lastname: Wibawan
authors.affiliation: Faculty of Veterinary Medicine, Department of Farm Animal Health, Utrecht University, Yalelaan 7, Utrecht 3584 CL, Netherlands.
authors.forename: Arjan
authors.initials: A
authors.lastname: Stegeman
authors.affiliation: Faculty of Veterinary Medicine, Department of Farm Animal Health, Utrecht University, Yalelaan 7, Utrecht 3584 CL, Netherlands.
authors.forename: Jan
authors.initials: J
authors.lastname: Van den Broek
authors.affiliation: Faculty of Veterinary Medicine, Department of Farm Animal Health, Utrecht University, Yalelaan 7, Utrecht 3584 CL, Netherlands.
authors.forename: Annemarie
authors.initials: A
authors.lastname: Bouma
mesh_terms: D000818:Animals; D002645:Chickens; D006385:Hemagglutination Inhibition Tests / Q000662:veterinary; D053124:Influenza A Virus, H5N1 Subtype / Q000235:genetics / Q000276:immunology*; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000276:immunology*; D005585:Influenza in Birds / Q000517:prevention & control* / Q000635:transmission*; D014611:Vaccination / Q000662:veterinary*; D015164:Vaccines, Inactivated / Q000008:administration & dosage / Q000276:immunology; D017201:Virus Shedding
chemical_list: D007252:Influenza Vaccines; D015164:Vaccines, Inactivated
keywords: Avian influenza; H5N1; Layer; Transmission; Vaccination