No abstract

The replicative abilities and tissue tropism properties of 13 non-pathogenic or low-pathogenic waterfowl-origin type A influenza isolates recovered in 1986 were examined in chickens. Following intravenous challenge, reisolation of challenge virus was attempted from swabs of the luminal surfaces of the cloaca, jejunum, ileum, bursa, trachea, and air sacs and from swabs of bone marrow and liver tissues. Virus-isolation attempts were also accomplished on brain, thymus, spleen, pancreas, gonad, kidney, blood, and lung tissues. The overall frequency of influenza virus recovery for each experiment ranged from 3.1% to 49.3%. For all experiments combined, 58.3% of the kidney tissues and 62.9% of the cloacal swab samples collected on days 1 to 10 postinoculation were positive for challenge virus recovery. Virus titers up to 10(8.7) mean embryo infective dose per gram of kidney tissue were demonstrated in clinically normal chickens. Distinct biological variations and nephrotropism appear to exist among the corporate properties of virus populations making up each of the 13 waterfowl-origin type A influenza isolates.

Because ducks are considered an important reservoir for type A influenza virus, and type A influenza viruses had not been recovered from ducks in Ohio, a 3-year virus surveillance study was conducted in Ohio waterfowl and waterfowl passing through Ohio to determine if domestic turkeys were at risk of exposure to avian influenza (AI) viruses from the waterfowl reservoir. The prevalence of AI infections in ducks during the fall migration averaged about 5.9%. The 55 waterfowl-origin type A influenza viruses recovered from ducks during fall 1986, 1987, and 1988 represented 23 different hemagglutinin-neuraminidase sub-type combinations of type A influenza viruses. Virus recovery frequencies ranged from 3.6% to 7.8% between years, from 2.0% to 8.2% between study sites, from 0.0% to 16.7% for sampling days, and from 0.0% to 14.3% among species of ducks sampled.

The potential of low pathogenicity (LP) avian influenza virus (AIV) isolates of wild bird origin to establish infection in commercial turkeys and broiler chickens was studied. Isolates, representing subtypes H5N1, H7N3, H6N2, and H3N6, were recovered in 2005 and 2006 from waterfowl and shorebirds in the Delmarva Peninsula region of the east coast of the United States. The LP AIV isolates were not pathogenic for 2-wk-old meat-type turkeys and broiler chickens. No mortality, clinical signs, or gross lesions were observed following intratracheal and conjunctival sac routes of exposures with 10(6.0) EID50 (embryo infectious dose) per bird. Isolates resulting in an established infection based on virus isolation were: A/mallard/Maryland/1159/ 2006 (H5N1) in the upper respiratory tract of turkeys; A/mallard/Delaware/418/2005 (H7N3) in the upper respiratory and intestinal tracts of turkeys and chickens; and A/shorebird-environment/Delaware/251/2005 (H3N6) in the upper respiratory and intestinal tracts of chickens. Infections were also confirmed by production of AIV-specific serum antibodies detected by hemagglutination inhibition.

Tissue tropism properties of A/chicken/Alabama/75 (H4N8) were examined after intravenous inoculation of 5-week-old specific-pathogen-free chickens. From 14 clinically normal chickens euthanatized on days 1-20 postinoculation, the frequencies of virus recovery were highest for cloacal swabs (86%), bursal swabs (64%), and kidney tissues (64%) and lowest for tracheal swabs (14%), thymus tissues (14%), bone-marrow swabs (7%), and brain tissues (0%). Evidence that the high frequency of virus recovery from kidney tissues was associated with virus replication in the kidney tissues was provided by high virus titers, ranging up to 10(9.5) mean embryo infectious dose per gram of kidney tissue, and by identification of intranuclear and intracytoplasmic type A influenza nucleoprotein in kidney cells using immunohistochemistry. Virus-recovery and virus titer results from three chickens that died on days 4 and 5 postinoculation paralleled the results from the clinically normal chickens. These findings indicate that A/chicken/Alabama/75 has nephrotropic properties similar to nephrotropic properties previously reported for waterfowl-origin type A influenza viruses and provide evidence that kidney lesions could be manifestations of systemic influenza infections in commercial laying chickens.