Observations on the implications of pathology induced by experimental schistosomiasis in baboons in evaluating the development of resistance to challenge infection

Abstract

SUMMARYLiver samples from 10Schistosomamansoni-infected baboons all yielded eggs but neither their egg counts nor duration of infection (< 226 weeks) correlated with the slightly elevated liver collagen levels or minimal histological fibrosis observed. Approximately 10% of inert 9 and 15 μm diameter microspheres injected into the mesenterio veins of 2 baboons with acute, challengeS. mansoniinfection reached their lungs (mainly 9 μm microspheres). Lung egg recoveries over 1000 were significantly less common among 175 baboons exposed once toS. monsoniinfections than among 56 baboons exposed more than once. Among 221S. mansoni-andS. haematobium-infected baboons, female worm, total tissue egg and lung egg recoveries were significantly correlated with each other but not with liver or (where available) spleen weights. Liver and spleen weights were strongly correlated with total body weight. Baboons did not develop significant liver fibrosis, even after prolonged schistosome infections. However, some liver ‘leakiness’ developed during acute primary and challenge infections, allowing small inert particles and eggs to pass to the lungs, but this ‘leakiness’ was not associated with resistance to challenge. In contrast to mice, such resistance in baboons cannot, therefore, be explained simply in terms of pathological changes due to previous infections.