West Nile Virus Infection in Horses: Detection by Immunohistochemistry, In Situ Hybridization, and ELISA.

This study describes the clinicopathologic findings in naturally occurring West Nile virus (WNV) infection in horses. WNV was diagnosed in a foal by immunohistochemical and in situ hybridization methods, and the presence of WNV antibodies was detected in 5 other horses with clinical signs suggestive of WNV infection. At necropsy of the foal, lymph nodes were edematous and enlarged, and the intestines showed diffuse congestion and focal hemorrhages. The most significant histologic lesions in this case were nonsuppurative meningoencephalomyelitis, particularly in the brainstem and spinal cord. Identification of viral RNA by in situ hybridization and viral antigen by immunohistochemistry was concentrated primarily in nerve fibers, glial cells, and their processes in brainstem and spinal cord and, to a lesser extent, within the cerebral hemispheres and cerebellum.