Tissue reactions to Schistosoma mansoni eggs

On the basis of tissue sections of the terminal ileum from mice infected with S. mansoni and killed at various intervals after exposure to cercariae, a correlation has been attempted between egg counts in the faeces and number of eggs at various levels of the intestinal wall. Between the 80th and 93rd day after infection an abrupt increase in the proportion of eggs diverted to the subserosa and muscular layers sets in, which is simultaneous with an increase in the intensity of the fibrotic reaction around eggs at these levels and in the submucosa. As a result, there is a sudden decrease in the numer of eggs arriving at the mucosa, which leads to a drop in egg excretion. However, all eggs succeeding in reaching the lamina propria of the villi are eliminated. Since most eggs in the stools are mature, this cannot simply be a passive process, and it is assumed that a histolytic enzyme secreted by the egg aids elimination.