The interaction between Schistosoma mansoni and platelets of non-immune mice has been studied in vivo and in vitro. A moderate thrombocytopaenia was observed in mice 2 days after they had been infected percutaneously with 200 cercariae. A rabbit anti-mouse platelet antiserum, 25 microL of which injected subcutaneously induced a nearly 900% reduction in blood platelet count 24 h later, was used to investigate the effects of severe thrombocytopaenia on S. mansoni infections. In replicate experiments worm burdens were significantly increased in mice that were thrombocytopaenic at the time of infection when compared with untreated mice. Induction of thrombocytopaenia on day 4 after infection had no effect on worm count. Platelets isolated from non-immune mice were shown to adhere to the surfaces of and kill mechanically transformed schistosomula in vitro. Platelets may thus be an innate mechanism of defence against schistosome infection, and the thrombocytopaenia that occurs during patent schistosome infections may be a strategy that helps secondarily incoming parasites evade this type of host defensiveness.

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: A cross-sectional epidemiological survey on Schistosoma haematobium infection was carried out in a small community in the coastal area of Kenya. From the 1,206 registered inhabitants, 853 urine specimens were examined. The overall prevalence and intensity of infection were 68.2 percent and 50.0/hour respectively. Some demographical and geographical differences of infection were analyzed. The profile of age-related distribution showed sexual differences in the prevalence and intensity of infection, the prevalence of heavy infection (>1,000/hour) and the prevalence of gross hematuria. Those of females are higher than those of males especially after adolescence. This is probably due to the difference in water contact behavior. The marked higher prevalence and intensity of infection were observed among people who lived along the branch of a main river than those who lived along the main river. The difference might be due to the different degree of contamination in the rivers. There was no difference in prevalence and intensity of infection among the three main tribes.

A statistical comparison was carried out among 3 different parameters, i. e. , egg count/volume, total egg countlsample and eggcountlhour, in regards to day-to-day variations of S. haematobium egg output in midday urination. Among 3 parameters, the egg countlhour showed the most stable value. In addition, the total egg cC?unt in a urine samplf7. was not correlated with the sample volume of the urine in the same individuals. We conclude, therefore, that the adoption of the egg countlhour was best as a parameter for a quantitative unit of intensity of infection for cohort studies where the changes of intensity of infection are monitored for a long period. The existing parameter for egg output expressed in terms of the egg countl10 mt volume of urine seems to be a less reliable reflection of the intensity of infection.

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