Blood platelets and schistosome egg excretion.

The eggs of helminths of the Schistosoma genus require to be extravasated in order to continue the life cycle of the parasite. The possible mode by which this takes place was investigated in a mouse model. Suppression of platelet activity in Schistosoma mansoni-infected mice by administering rabbit anti-mouse platelet serum or a selection of "antiplatelet drugs" resulted in a significant reduction of parasite egg excretion. This reduction was best achieved when antiplatelet agents were administered just before the onset of parasite egg excretion. The association between parasite eggs and platelets was illustrated in vivo and in vitro where platelet aggregates on egg surfaces were seen in both light and electron microscopy. In addition, eggs that had been isolated from infected mouse tissues induced platelet aggregation in whole mouse blood, and this was inhibited by preincubation with the beta-lactam antibiotic, ticarcillin. Isolated eggs were also capable of inducing ex vivo platelet aggregation in mice, which was dependent on presensitization with eggs. These data suggest a role for platelets in the extravasation and excretion of parasite eggs in schistosomiasis.