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

Abstract

The pathogenesis, virus shedding, and serologic response in specific-pathogen-free (SPF) 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 10(6) EID50 of LPAI per bird, intrachoanally, and examined for clinical signs for 3 wk. Oropharyngeal and cloacal swabs, and fecal samples, were collected at 2, 4, and 7 days postinoculation (PI) for virus detection by real-time 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 tests. Tissue samples for histopathology were collected from three birds per group at 3 days PI. The hemagglutinin 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 were commercial turkeys. Microscopic lesion results in both species showed the predominance of lesions in the respiratory and gastrointestinal 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 for surveillance and control because some of the LPAI viruses (of wild bird origin and examined in this study) that can infect and be shed by chickens and turkeys would be difficult to detect in commercial poultry. Specifically, detection is difficult because these viruses did not cause overt clinical disease or mortality, but only induced mild microscopic lesions and exhibited poor seroconversion.