Histopathological observations on experimental Trypanosoma evansi infection in bovine calves.

Experimental trypanosomosis was produced in 4 cross-bred bovine calves by subcutaneous inoculation of 5x107Trypanosoma evansi on days 0 and 14. The calves developed pyrexia and generalised weakness with occasional parasitaemia. The gross lesions included paleness of visceral organs, gelatinisation of fat, enlarged spleen and marked congestion of lungs. Microscopic examination revealed lymphoid depletion and necrosis together with moderate haemosiderosis in spleen. The liver lobules showed dilated spaces of Disse and fibrocellular reaction in portal triads. Lungs showed septal thickening, cellular infiltration and engorged capillaries. The interstitial connective tissue between the cardiac muscle bundles was loosened with mild fibrocellular reaction, occasionally with degenerated muscle fibres. Lymphoid depletion in spleen may be correlated to the possible immunosuppression caused by T. evansi.