Observations on bilharziasis of domestic ruminants in South Africa

Abstract

Bilharziasis of 100 sheep and 14 cattle caused by Schistosoma mattheei Veglia & Le Roux, 1929, was studied in detail from the histopathological aspect. The ovine cases included natural as well as experimentally infested animals. The most significant changes resulted from the presence of schistosome ova and the dead schistosomes in the branches of the intrahepatic portal vein. The host reaction to the ova is of a granulomatous nature which is interpreted as a type of delayed hypersensitivity reaction. In a few cases there was an even more marked sensitivity superimposed on this. It was characterized by concentrations of eosinophiles around miracidial-containing ova as well as shells of ova present in the centre of mature granulomas. This was accompanied by necrosis of adjacent liver cord cells and necrosis of masses of eosinophiles. This appears to be analogous to the toxaemic form of human bilharziasis. In both sheep and cattle, particularly the latter, the host response to dead adult schistosomes in the intrahepatic branches of the portal vein was striking. The initial thrombosis was followed by a granulomatous response to remove the parasite, and a localized lymphoid proliferation which destroyed the wall of the vein and remained after the schistosome had been removed. The Hoeppli phenomenon occurred in response to ova in both sheep and cattle; being more pronounced and more frequently present in cattle. The conclusion is drawn by the authors that cattle are less affected by bilharziasis than sheep and goats.