Population biology of Schistosoma mansoni in the black rat: host regulation and basic transmission rate.

A simple mathematical model was built to investigate the population biology of Schistosoma mansoni in its natural definitive host, the black rat (Rattus rattus). Prevalence and parasite abundance over 13 years from field studies and data from laboratory experiments were used to set up the model. Sensitivity analysis showed that the abundance of parasites is strongly influenced by variation in the values of infection parameters. The model shows that the parasite is able to control populations of definitive hosts. We discuss the factors that may explain the long-term persistence of S. mansoni among its natural definitive host, R. rattus and its intermediate host, the snail Biomphalaria glabrata in Guadeloupe (French West Indies). The impact of the parasite does not appear to explain the apparent persistence of the host-parasite association over a 13 year period. Our results seem to support the influence of environmental factors, which may act on the infection process by reducing, or increasing, the rate of encounters between hosts and free-living stages of the parasite.