A 12-month-old crossbred bull was submitted to the Texas A&M Veterinary Diagnostic Laboratory (TVMDL) in College Station for necropsy. The clinical history indicated that this animal had periodic seizures and bouts of ataxia for two days. The animal would appear to be normal between these neurologic episodes. The referring veterinarian indicated that the neurologic signs could be triggered by making the animal move. The animal died two days after first exhibiting neurologic signs. The primary lesions observed at necropsy were dark red lungs that exuded a clear fluid on the cut surface and a lack of feces in the distal colon.
The most important histologic lesion was moderate colitis with numerous developmental stages of coccidia within the epithelial cells. In some areas, the luminal mucosa was eroded. The lumen contained numerous mature coccidia.
Nervous coccidiosis is usually a problem in feedlots when the weather is cold. In herd epidemics of coccidiosis, approximately 20% of the affected cattle may have nervous signs. The fatality rate of animals affected with nervous coccidiosis is approximately 50%. The primary coccidial agents associated with nervous coccidiosis are Eimeria zuernii and Eimeria bovis. The underlying cause of the nervous signs associated with nervous coccidiosis is inconclusive. Some studies have proposed a neurotoxin found in the blood of affected animals while other studies propose an underlying electrolyte imbalance caused by diarrhea associated with coccidiosis. Regardless, histologic lesions are not observed in the brain of affected animals. The diagnosis of nervous coccidiosis is based upon the clinical signs, large numbers of coccidia in the feces and a lack of histologic lesions in the brain.
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