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Title: Biologic characterization of H4, H6, and H9 type low pathogenicity avian influenza viruses from wild birds in chickens and turkeys

Author
item MORALES,JR., ANTONIO - University Of Georgia
item HILT, DEBORAH - University Of Georgia
item WILLIAMS, SUSAN - University Of Georgia
item Pantin Jackwood, Mary
item Suarez, David
item Spackman, Erica
item STALLKNECHT, DAVID - University Of Georgia
item JACKWOOD, MARK - University Of Georgia

Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/29/2009
Publication Date: 12/5/2009
Citation: Morales,Jr., A., Hilt, D.A., Williams, S.M., Pantin Jackwood, M.J., Suarez, D.L., Spackman, E., Stallknecht, D.E., Jackwood, M.W. 2009. Biologic characterization of H4, H6, and H9 type low pathogenicity avian influenza viruses from wild birds in chickens and turkeys. Avian Diseases. 53:552-562.

Interpretive Summary: Avian influenza is a severe disease of poultry, including chickens and turkeys. Ducks and wild aquatic birds are the natural reservoirs of low pathogenic avian influenza (LPAI) viruses. In this study, specific pathogen-free (SPF) chickens and commercial turkeys were infected with H4, H6, and H9 type low pathogenic avian influenza viruses (LPAI) isolated from wild birds, and clinical signs, shedding of the virus, and production of antibodies against avian influenza virus (AIV) after infection were determined. Tissue samples were collected from infected birds and examined for microscopic lesions. The hemagglutinin (HA) genes of the viruses were also sequenced and phylogenetic analysis was conducted. Clinical signs ranged from no clinical signs to moderate depression, decreased activity and decreased food and water consumption. Based on virus detection results, SPF chickens were generally found to be shedding more virus than commercial turkeys. Microscopic lesions were commonly found in the respiratory and gastro-intestinal tract, which is consistent with the fact that these viruses are of low pathogenicity. Turkeys had fewer lesions in the respiratory tract and more lesions in the gastrointestinal tract compared to chickens. Thirteen LPAI viruses induced production of antibodies against AIV in commercial turkeys whereas only 6 LPAI viruses did so in SPF chickens. Phylogenetic analysis of the of the HA genes showed that the H4, H6 and H9 viruses evaluated here represented the full genetic diversity of North American AIVs of their respective subtypes. This data is important with regard to surveillance and control of avian influenza since some of the LPAI viruses of wild birds examined in this study that can infect chickens and turkeys would be difficult to detect in commercial poultry because these viruses did not cause evident clinical disease or mortality.

Technical Abstract: In this study, the pathogenesis, virus shedding and serologic response in specific pathogen-free chickens and commercial turkeys against H4, H6, and H9 type low pathogenic avian influenza viruses (LPAI) from wild birds was examined. Four week old chickens and three week old turkeys were given 1 x 106 embryo infective dose50 of LPAI per bird and examined for clinical signs for 3 weeks. Oropharyngeal and cloacal swabs, and fecal samples were collected at 2, 4 and 7 days post-inoculation (PI) for virus detection by real time real-time reverse transcriptase polymerase chain reaction (RT-PCR). Serum was collected at 7, 14 and 21 days PI and examined for antibodies against avian influenza virus (AIV) by the enzyme linked immunosorbant assay (ELISA) and hemagglutination inhibition (HI) tests. Tissue samples for histopathology were collected from 3 birds per group at 3 days PI. The hemagglutinin (HA) genes of the viruses were sequenced and phylogenetic analysis was conducted. Clinical signs ranged from no clinical signs to moderate depression, decreased activity and decreased food and water consumption. Based on virus detection results, SPF chickens were generally found to be shedding more virus from both the oropharynx and cloaca than commercial turkeys. Histopathological results in both species showed the predominance of lesions in the respiratory and gastro-intestinal tract, which is consistent with the fact that these viruses are of low pathogenicity. In chickens and turkeys, oropharyngeal shedding strongly correlated with the lesions found in the upper respiratory tract. Turkeys had fewer lesions in the respiratory tract and more lesions in the gastrointestinal tract compared to chickens. Thirteen LPAI viruses caused seroconversion in commercial turkeys whereas only 6 LPAI viruses caused seroconversion in SPF chickens. Phylogenetic analysis of the HA genes showed that the H4, H6 and H9 viruses evaluated here represented the full genetic diversity of North American AIVs of their respective subtypes. This data is important with regard to surveillance and control since some of the LPAI viruses of wild bird origin examined in this study that can infect and be shed by chickens and turkeys would be difficult to detect in commercial poultry because these viruses did not cause overt clinical disease or mortality, induced mild microscopic lesions, and poor seroconversion.