Clinical findings, lesions, and viral antigen distribution in great gray owls (Strix nebulosa) and barred owls (Strix varia) with spontaneous West Nile virus infection.

West Nile Virus (WNV) infection manifests itself clinically and pathologically differently in various species of birds. The clinicopathologic findings and WNV antigen tissue distribution of six great gray owls (Strix nebulosa) and two barred owls (Strix varia) with WNV infection are described in this report. Great gray owls usually live in northern Canada, whereas the phylogenetically related barred owls are native to the midwestern and eastern United States and southern Canada. Naturally acquired WNV infection caused death essentially without previous signs of disease in the six great gray owls during a mortality event. Lesions of WNV infection were dominated by hepatic and splenic necrosis, with evidence of disseminated intravascular coagulation in the great gray owls. WNV antigen was widely distributed in the organs of the great gray owls and appeared to target endothelial cells, macrophages, and hepatocytes. The barred owls represented two sporadic cases. They had neurologic disease with mental dullness that led to euthanasia. These birds had mild to moderate lymphoplasmacytic encephalitis with glial nodules and lymphoplasmacytic pectenitis. WNV antigen was sparse in barred owls and only present in a few brain neurons and renal tubular epithelial cells. The cause of the different manifestations of WNV disease in these fairly closely related owl species is uncertain.