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2007 ACVP Annual Meeting

2007 ACVP/AAVLD Diagnostic Travel Award

First Place: $1,000 Grant

CENTRAL NERVOUS SYSTEM PATHOLOGY OF NATURALLY OCCURRING TRYPANOSOMA EVANSI INFECTION IN HORSES. A. Rodrigues1, R. A. Fighera2, T. M. Souza2, C. S. L. Barros2. 1Department of Veterinary Pathobiology, College of Veterinary Medicine, Texas A&M University, College Station, TX, USA. 2Laboratory of Veterinary Pathology, Departamento de Patologia Veterinaria, Universidade Federal de Santa Maria, Santa Maria, RS, Brazil.
Nine cases of naturally occurring infection of the central nervous system by Trypanosoma evansi were diagnosed in horses in the state of Rio Grande do Sul, Southern Brazil, from 2003 to 2006. The clinical course ranged from 2-20 days, and clinical signs included marked ataxia, blindness, circling, hyperexcitability, obtundation, proprioceptive deficits, falling down, head tilt, head pressing and recumbency with paddling movements. On gross examination, seven of the nine horses had gross lesions consisting of asymmetric flattening of gyri and focally extensive areas of yellow discoloration and softening of white matter. Histologically, the brains of all nine horses displayed an overwhelming necrotizing panencephalitis characterized by marked edema, demyelination, and a heavy perivascular infiltrate of mononuclear cells; these changes were more prominent in the white matter. The inflammatory infiltrate consisted of lymphocytes and plasma cells, the latter often containing eosinophilic cytoplasmic globules (Mott cells). Mild to moderate meningomyelitis and/or meningitis were observed in the spinal cord of 5/7 horses. T. evansi was demonstrated immunohistochemically in the perivascular spaces, neuropil and white matter parenchyma of formalin-fixed paraffin-embedded brain tissue of eight out of the nine affected horses.

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