Leukoencephalomalacia Outbreak in Horses due to Consumption of Contaminated Hay

Fumonisins are thermostable toxins produced by Fusarium spp. These fungi commonly contaminate corn and other types of cereal; nevertheless, they rarely contaminate hay, and when contamination occurs, it is uncommonly a toxic strain. These mycotoxins were first described by a study group in South Africa after 20 years of searching for the substance produced by F. moniliforme that causes leukoencephalomalacia. There are 2 types of fumonisins among the varieties previously described that can cause neurological conditions, that is, fumonisins B1 and B2, which are produced by 3 species of Fusarium: F. moniliforme, F. proliferatum, and F. subglutinans. The first species is most frequently isolated worldwide. The mycoflora of 39 concentrated samples associated with confirmed leukoencephalomalacia cases in Brazil has been reported; F. moniliforme was found in 82%, F. proliferatum in 12.8%, and F. subglutinans in 2.6% of samples. In the United States, from the fall of 1989 to the winter of 1990, 45 samples of feed obtained from confirmed leukoencephalomalacia cases contained F. moniliforme, as did samples obtained from cases from Mexico. Animals affected by leukoencephalomalacia die suddenly, with or without the occurrence of clinical manifestations. The common manifestations are anorexia, lethargy, hypersensitivity and agitation, sweating, muscle fasciculation and weakness, hypermetria, staggering, circling, inability to swallow, blindness, dilated pupils, absence of a pupillary light reflex, head pressing, and tonic-clonic seizures. This disease should be considered in the differential diagnosis of traumatic brain injury, arboviral encephalitis, hepatic encephalopathy, equine protozoal myeloencephalitis, Theiler’s disease, and botulism. The histopathological lesions noted in the central nervous system include hemorrhage, malacia, and perivascular congestion involving the white matter of the brain. In the liver, lobular necrosis, periportal fibrosis, periportal vacuolation, and a proliferation of bile ducts can be found. Leukoencephalomalacia is a well-known disease in veterinary medicine. The disease is difficult to diagnose, which delay adequate treatment and management, resulting in the death of many animals. Fungal isolation and quantification of fungal mycotoxins on grain are commonly performed when there is a suspicion of leukoencephalomalacia; however, this procedure is rarely carried out on hay. We found no study in the literature describing this disease as a result of eating contaminated hay.