Clinical and epidemiologic features of an epizootic of equine leukoencephalomalacia.

A herd of 15 mature riding horses with a history of anorexia, weight loss, and lethargy was examined. The animals had been fed a 50/50 mixture of commercial sweet feed and corn screenings contaminated with a heavy growth of Fusarium moniliforme. Thirteen of the horses had one or more neurologic signs. The most characteristic signs were profound depression and mild ataxia. Over the 19-day course of the epizootic, the horses had increasing severe neurologic deficits, including unilateral blindness and delirium. Despite the clinical appearance of dehydration, 12 horses had low PCV (16 to 27%), hematocrit (21.2 to 31.0%; determined by automated cell counter), and RBC counts (3.76 to 5.5 x 10(6) RBC/microliters). White blood cell counts were variable (4,900 to 17,000 WBC/microliters). Necropsy findings included diffuse malacia of the white matter of the frontal cortex and severe multifocal perivascular hemorrhage in the white matter of the temporal cortex, basal ganglia, anterior medulla, and pons. One horse had a hepatic lesion consisting of a mixed inflammatory cell infiltrate and bile duct proliferation. The attack rate of this epizootic was 100%. The course of disease was unusually long in some animals. In an experiment, the fusarium-infected corn screenings were fed to horses and did not cause clinical signs or alterations in blood or serum biochemical values.