Pathology and tissue distribution of West Nile virus in North American owls (family: Strigidae).

This study describes the macroscopic and microscopic lesions and the viral antigen distribution in 82 owls (Family: Strigidae) of 11 North American and one Eurasian species that died following natural West Nile virus infection. The range of lesions seen was greater than that previously reported for owls, and involved more organs. Two patterns of antigen distribution were identified: one that involved the blood and all major organs; and a second where antigen was sparse, localized, and absent from the blood. The first pattern was associated with species of northern natural breeding range, while the second was seen in owls of a more southern distribution and appeared to be associated with a more prolonged course of illness. Further differences in lesion and antigen distribution appeared to be either species related or individual. The findings underline the complexity and variability of West Nile virus pathology within birds of a relatively narrow taxonomic group.