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The study of the rate of contamination of B. glabrata and the cercarial densities of S. mansoni in the chanels of Beaugendre valley (Guadeloupe, French West Indies) concentrates attention on the focalisation of the sites with high risk of contamination. This focalization of the sites of transmission is directly related to the regular deposition of human faeces. A small number of contamined people is enough to maintain high cercarial densities (230 c/1). In the chanel studied, the role of the rat in the transmission of the parasite seems less important than that of the Man. The infection of the rats during consumption of snails can be foreseen.

Neopolystoma euzeti n. sp., a parasite of the urinary bladder and the rectum of the freshwater tortoise Clemys caspica var. leprosa in Tunisia, is mainly characterized by its genital spines in high number (33 to 36) and the very important extension of the vitellaria. It is the first species of the genus Neopolystoma Price, 1939, to be described in Africa, the others being known from North America, Japan and Eastern Siberia.

In Guadeloupe (French Lesser Antilles), because they are simultaneously infested with Schistosoma mansoni, which causes the human intestinal schistosomiasis, and Ribeiroia marini, a Trematode which sterilizes the Mollusk-host of the schistosoma, the rats (Rattus rattus and Rattus norvegicus) seem able to influence, at least locally, the infestation of the human population.

From 1971 until 1982, we studied the ecological factors which stead fast a perennial schistosomiasis in Guadeloupe on an exhaustive mode. More recently, we start a similar investigation in Martinique. In Guadeloupe the single vector of Schistosoma mansoni is the snail Biomphalaria glabrata which is an ubiquist species. But the transmission to man is restricted to the "canal-sewers" where faeces are dropped and not in the rivers of Basse-Terre or the ponds of Grande-Terre. Moreover, the infection is possible only during the hottest hours of the day, when the cercariae get out of the snail. We built a "cercariometer" with which we are able to know the number of cercariae per litre in a given place at every hour of day and night. The black rat (and not the grey rat!) seems, alone, able to maintain the life-cycle of the parasite, at least in the mangrove forests. It is now possible to "clone" S. mansoni by sporocysts transplantation in non-infected snails. The biological control of B. glabrata populations is possible by sterilizating Trematodes such as Ribeiroia guadeloupensis. A new built irrigation reservoir in Grande-Terre give a chance of spread for the endemy in an area which was, till now, unharmed.

The laurylamidopropylbétaïne, a surface active substance, has been tested in field conditions, in Niger, against Schistosoma mansoni miracidia. Experiments were carried out in artificial ponds of 20 m3, in which conditions were similar, as far as possible, to conditions found in transmission sites. The product showed a satisfactory remanence and the percentage of infected molluscs dropped down to zero with a low (2 ppm) concentration. It is suggested that laurylamidopropylbetaïne could be used into soaps in order to renew constantly the product in washing and bathing places and reduce schistosome transmission.