Clinical and epidemiologic features of an epizootic of equine leukoencephalomalacia.

This study investigated an outbreak of severe neurological disorder in a group of riding horses, which was associated with their consumption of feed contaminated with Fusarium moniliforme fungus. The researchers described the clinical and epidemiological characteristics of the disease, ultimately finding that the fungal-contaminated feed was most likely the cause of the disease.

Background and Study Approach

• The research was carried out on a herd of 15 mature riding horses that displayed symptoms like anorexia, weight loss, lethargy, and neurological signs such as depression and mild ataxia. It was observed these symptoms increased over a 19-day period, progressing to severe neurological deficits such as blindness and delirium. All these horses had been fed a mix of commercial sweet feed and Fusarium moniliforme-contaminated corn screenings.
• The researchers carried out an in-depth examination of the horses and performed necropsies (post-mortem examinations) on deceased animals.

Clinical Findings

• The researchers observed that despite the clinical appearance of dehydration, 12 of the horses had low Packed Cell Volume (PCV), which is a measure of the proportion of blood volume that is occupied by red blood cells.
• Low Hematocrit and Red Blood Cell (RBC) counts, which are also measures of the proportion of red blood cells in the blood, were observed. These findings suggest an abnormality in the blood composition of the affected horses.
• The White Blood Cell (WBC) counts varied amongst the affected horses.
• On performing necropsies, the researchers discovered abnormal changes in the brain tissues, including extensive damage to the white matter of the frontal and temporal cortices, basal ganglia, anterior medulla, and pons. These are regions critical for motor control and cognitive functions.
• One horse also exhibited a hepatic (liver) lesion consisting of inflammation and bile duct proliferation, indicating a possible impact on the liver.

Epidemiological Findings

• The research highlights that the incidence rate of the disease during the study period was 100%, suggesting a highly infectious nature of the causative agent or conditions.
• In some of the horses, the disease took an unusually long course, indicating variability in the disease progression and severity amongst the affected individuals.
• In an attempt to reproduce the disease, the researchers fed the Fusarium-contaminated corn screenings to other horses, but this did not result in the same clinical signs or changes in blood or serum biochemical values. This suggests that the disease could result from multiple factors or require specific conditions for its manifestation.

Conclusion

• The study therefore concluded that the outbreak of this severe neurological disorder in the horses was most likely due to their consumption of the feed contaminated with Fusarium moniliforme fungus, a type of mold that is harmful to horses.
• The variety of symptoms, blood abnormalities and varying disease courses suggest that the disease is complex, and further research is required to understand the exact cause and mechanism.