Pathological studies of A/chicken/Alabama/7395/75 (H4N8) influenza virus in specific-pathogen-free laying hens.

Specific-pathogen-free laying hens were inoculated with avian influenza virus (AIV) A/chicken/Alabama/7395/75 (H4N8) either intratracheally (IT) or intravenously (IV). IT inoculation produced a localized infection of the upper and lower respiratory tracts with lesions of tracheitis, bronchitis, airsacculitis, and pneumonia around the secondary bronchi. IV inoculation produced a systemic infection with major lesions of nephritis, interstitial pneumonia, salpingitis, and splenic and hepatic necrosis. In IV-inoculated hens, AIV nucleo-protein was demonstrated within renal tubule epithelium, in luminal surface and glandular oviduct epithelium, and in mononuclear cells within pulmonary blood capillaries. However, no virus was recovered from internal contents of eggs laid between days 1.5 and 5 postinfection. These data indicate that A/chicken/Alabama/7395/75 has tissue tropism and pathogenicity for the respiratory and urogenital systems of reproductively active laying hens. Site and severity of lesion development are determined by the localized or systemic nature of AIV infection.