Clinical and Pathologic Features of West Nile Virus Infection in Native North American Owls (Family Strigidae)

Since the initial report of West Nile virus in the northeastern United States in 1999, the virus has spread rapidly westward and southward across the country. In the summer of 2002, several midwestern states reported increased cases of neurologic disease and mortality associated with West Nile virus infection in various native North American owl species. This report summarizes the clinical and pathologic findings for 13 captive and free-ranging owls. Affected species were all in the family Strigidae and included seven snowy owls (Nyctea scandiaca), four great-horned owls (Bubo virginianus), a barred owl (Strix varia), and a short-eared owl (Asio flammeus). Neurologic signs identified included head tilt, uncoordinated flight, paralysis, tremors, and seizures. Owls that died were screened for flaviviral proteins by immunohistochemical staining of formalin-fixed tissues, followed by specific polymerase chain reaction assay to confirm West Nile virus with fresh tissues when available. Microscopic lesions were widespread, involving brain, heart, liver, kidney, and spleen, and were typically nonsuppurative with infiltration by predominantly lymphocytes and plasma cells. Lesions in owls were much more severe than those previously reported in corvids such as crows, which are considered highly susceptible to infection and are routinely used as sentinel species for monitoring for the presence and spread of West Nile virus. This report is the first detailed description of the pathology of West Nile virus infection in Strigiformes and indicates that this bird family is susceptible to natural infection with West Nile virus.Original Abstract: Caracteristicas clinicas y patologicas de la infeccion por el virus del Nilo en buhos nativos de Norteamerica (familia Strigidae). Delta espues del reporte inicial de la presencia del virus del Nilo en Estados Unidos en 1999, el mismo se ha diseminado rapidamente hacia el este y sur del pais. En el verano del 2002, algunos estados de la region del oeste medio de los Estados Unidos reportaron un aumento de los casos de enfermedades neurologicas y mortalidad asociadas a infecciones por el virus del Nilo en varias especies de buhos nativos de Norteamerica. En este reporte se describen los hallazgos clinicos y patologicos encontrados en 13 buhos en cautiverio y silvestres. Todas las especies afectadas pertenecian a la familia Strigidae, incluyendo siete buhos nivales (Nyctea scandiaca), cuatro buhos de Virginia (Bubo virginianus), un c