Schistosoma egg

Schistosomes are parasites of the vasculature of their hosts. While the intravascular niche provides a rich source of nutrition, the location deep within tissues presents a major problem, namely, dispersal of offspring into the environment where they can infect the intermediate host. The eggs themselves orchestrate their escape, by inducing an intense cellular response that forces the egg across the endothelium and the lining tissues of organs such as the intestine or urinary bladder. The ova and oogenesis are treated by Grevelding et al., Chapter 15. The eggs are central in pathogenesis and diagnosis of schistosomiasis. The females and the males, prior to reproductive maturation, will pair and then migrate to the mesenteric veins of the host, where the females will lay hundreds of eggs daily (Wilson et al. 2007). In the case of S. mansoni, adult worm pairs lay approximately 350 eggs per day and S. japonicum lay approximately three times more (Cheever et al. 1994). About a third to one half of the eggs released by the females will not reach the external environment (Cheever et al. 1994; Pearce and MacDonald 2002)