Studies on American Paragonimiasis. I. Age Immunity of the Snail Host

Abstract

r: Apparent age immunity of the snail Pomatiopsis lapidaria (Say) from Louisiana to infection by Paragonimus kellicotti Ward, 1908, also from Louisiana, is demonstrated. Studies of age immunity of snails to infection by digenetic trematodes have been few. To this author's knowledge there is no report in the literature of a study of differential susceptibility of different size (and hence age) snails to infection by miracidia of Paragonimus kellicotti Ward, 1908, except the statement by Ameel (1934) that small (about 1 mm), but not larger, specimens of Pomatiopsis lapidaria (Say) from Michigan were susceptible to infection. He found 100% susceptibility in these small snails. Dundee (1957) and Sogandares and Malek (1963) have respectively observed that P. lapidaria probably has two breeding periods a year in Michigan and Louisiana. According to Dundee's (1957) data, a snail about 1 mm long would be about 5 weeks old since the growth increment is about 0.1 + mm per week and the snails are about 0.5 mm long when