Approche expérimentale du rôle de Rattus rattus et de Rattus norvegicus dans le foyer de Schistosoma mansoni de Guadeloupe

Abstract

We have studied the development of Schistosoma mansoni in two natural hosts, Rattus rattus and Rattus norvegicus, and in two laboratory hosts, the white Mouse and the white Rat. The study of survival shows that the percentage of cercariae recovered as adult worms four weeks after exposure is 31% in R. rattus, 27% in the white Mouse, 14% in the laboratory Rat and 12% in R. norvegicus. Twenty weeks after exposure, 62% of the Schistosomes which were present four weeks after exposure are still alive in the Mouse, 48% in R. rattus, 8% in R. norvegicus and 5% in the laboratory Rat. The study of growth shows that the average size of males eight weeks after exposure is 7 mm in the Mouse, 5.1 mm in R. rattus, 2.9 mm in the white Rat and 2.6 mm in R. norvegicus. The study of egg production shows that S. mansoni lays eggs in the four Rodents; however only mice and R. rattus eliminate fertile eggs containing infectious miracidia of S. mansoni; in R. norvegicus, as in the white Rat, the eggs of S. mansoni are not fertile and are never eliminated by the host. These results demonstrate that susceptibility is not always associated with permissivity and there is a great difference between the two natural hosts; R. norvegicus accepts S. mansoni but does not allow its transmission; R. rattus which is more favourable to growth and reproduction of S. mansoni, allows the transit and exit of fertile eggs. These experimental data indicate that R. rattus is able to play a part in the dynamics of the guadeloupean schistosomiasis focus while R. norvegicus is unable to contribute to the circulation of S. mansoni and is a decoy host for the parasite.