Fig 3

Diagrammatic representation of the fate of migrating schistosomula in normal and vaccinated mice. a Cumulative parasite deaths in the lungs. b Cumulative parasite survival and development in the portal system. The diagrams are based on the spreadsheet calculation in Additional file 1: Table S1. For simplicity, the model assumes that parasites end their migration either in the lungs or the portal system. After an initial elongation phase of about three days in the lungs, the time-base of a circuit around the body in the bloodstream is approximately 48 h. An average P = 0.36 of getting stuck in the lungs of a naïve mouse on each passage produces an adult worm portal population equal to 32 % of penetrating cercariae (red line). A “protection” of 40 % induced by a vaccine needs to increase the P of getting stuck to 0.53, with 13 more parasites trapped (blue line). A “protection” of 70 % needs a P of 0.72, with 22 more worms trapped. This is still only one quarter of the total losses