Schistosoma mattheei in the ox: Observations on the parasite

Abstract

Nineteen Friesian steers infested with between 5 000 and 45 000 cercariae of Schistosoma mattheei were slaughtered at intervals between 7 and 107 weeks post-infestation and the parasites were recovered by perfusion of the blood vessels. Adult parasites were eliminated as infestation progressed, the greatest loss occurring between 18 and 40 weeks. Females in the mesentery became shorter as infestation progressed but males remained unchanged. Males from the gastric veins were sometimes longer than those from the mesentery while males and females from liver and lungs were often shorter. Females from the mesentery contained 0–107 eggs, with a mean of 36, and those from liver and lung contained fewer eggs. The prepatent period was 6–7 weeks. A sharp reduction in faecal egg count between 15 and 25 weeks post-infestation was caused by a reduction in oviposition. The marked changes in the number of parasites present, their length and their egg-laying capacity appeared to be mediated by the immune response of the host and were manifestations of the establishment of a biological equilibrium which limited the pathogenic effects of the parasite.