Infecção natural por Trypanosoma evansi em eqüinos

Abstract

Cases of trypanosomiasis by Trypanosoma evansi were diagnosed in horses in the state of Rio Grande do Sul, Brazil, between 2003 and 2006. In one stud farm (Farm A) with 125 horses, 53 died. Additionally, around 80 mares were sent to Farm A to be bred. Of those, 66 became ill and 56 died after being returned to their farms of origin. Twenty three horses clinically affected by the disease were observed. Clinical signs included loss of weight (despite voracious appetite), lethargy, incoordination and instability of hindlimbs, atrophy of the large muscles of the hindlimbs, muscle weakness and paleness of mucosae. Specimens of T. evansi were detected in the blood drawn from four affected horses. Normocytic normochromic anemia with PCVs ranging from 15 to 31%, leucocytosis due to lymphocytosis associated to large atypical lymphocytes was observed in several affected horses. High levels of antibodies against T. evansi were detected in the serum of fifteen horses. Ten horses presented encephalic neurological signs such as circling, ataxia, blindness, excitation, falls, listlessness, proprioception deficits and head tilt. One horse assumed a dog-seating position . Necropsy findings included muscle atrophy, enlargement and lymphoid hyperplasia of the spleen and lymphnodes. Seven out of the 9 necropsied horses with encephalic signs had asymmetrical gross lesions in the brain consisting of flattening of gyri and focal extensive areas of yellow discoloration and softening of white matter. Histologically, an overwhelming necrotizing anencephalitis was observed in all 9 horses with encephalic neurological signs. This panencephalitis was characterized by marked edema, demyelination and malacia, and perivascular infiltrates of up to 20 rows of mononuclear cells affecting mainly the white matter. Several plasma cells in the inflammatory infiltrate contained numerous eosinophilic globules (Mott cells) or homogenous bright-red material (flame cells) in their cytoplasm. Mild to moderate meningomyelitis and/or meningitis were observed in the spinal cord of 5 horses. Similar histological lesions were observed in the spinal cord of the horse with the dog-seating position . The brains of nine horses with the encephalic signs were submitted to immunohistochemistry stain by the streptavidin-biotin technique. In eight brains moderate to abundant specimens of T. evansi in the perivascular spaces and neuropile were marked by the specific antibody.