An epizootic attributable to western equine encephalitis virus infection in emus in Texas.

An epizootic of encephalomyelitis attributable to western equine encephalitis virus was identified in emus (Dromaius novaehollandiae) from several flocks in western Texas in July 1992. Affected emus ranged from 3 months to 3 years old. Morbidity of emus in 8 flocks ranged from 15 to 50%, and 17 of 193 (8.8%) emus died. The diagnosis was confirmed by isolation and characterization of the causative virus and detection of antibody to the virus in emus that were currently ill and emus that had been ill but recovered. Clinical signs varied from mild to severe and included anorexia, lethargy with sternal recumbency, ataxia, muscle tremors, head tilt, unnatural positioning of the head on the back, acute onset of paralysis, and lateral recumbency with paddling. A few emus died without prior evidence of clinical disease. Post-mortem examination revealed 3 to 5 ml of clear pale-yellow pericardial fluid that contained a fibrin clot. Volume of the contents of the proventriculus and ventriculus were less than anticipated. Microscopic examination of numerous tissues revealed multifocal vasculitis with infiltration of plasmacytes, lymphocytes, and a few heterophilic leukocytes. The epizootic developed during a period of unseasonably heavy rainfall that resulted in higher numbers of mosquitoes than was typical for that season of year. A concurrent increase in the number of horses with encephalomyelitis attributable to western equine encephalities virus was not reported.