Ataxia in four horses with equine infectious anemia.

In 4 horses with equine infectious anemia (EIA), the predominant clinical sign was ataxia. Other clinical and laboratory findings often associated with EIA included weight loss, anemia, pyrexia, thrombocytopenia, hemorrhages, hypergammaglobulinemia, and high activity of biliary epithelial enzymes. Neuropathologic findings were nonsuppurative granulomatous ependymitis, meningitis, and encephalomyelitis and plasmacytic-lymphocytic infiltration of the brain and spinal cord. The onset of neurologic signs corresponded to the acute stage of infection in at least 2 horses, and the signs developed at least 18 months after infection in 1 case. Cerebrospinal fluid from 3 of the horses contained high concentration of protein and white cells, although changes in 1 horse may have been associated with a prior traumatic attempt to collect CSF. By comparison, CSF from 3 ponies inapparently infected with EIA was normal. Active production of anti-EIA antibody in the CSF was suspected on the basis of serologic findings.