Infectivity of Echinostoma revolutum Miracidia for Laboratory-Raised Pulmonate Snails

Abstract

With respect to the first intermediate host, Echinostoma revolutum is considered to be less specific than most trematodes. In his studies on that species, Beaver (1937, Illinois Biological Monographs 15: 1-96) utilized Helisoma trivolvis as that host and tabulated, from the world literature, pulmonate species representing 6 genera and reported to serve E. revolutum in that capacity. After the discovery of E. revolutum in H. trivolvis from ponds in eastern Pennsylvania, periodic examinations of snails from that area revealed the infection only in that species. More recently, laboratory-raised snails were exposed to miracidia ofE. revolutum; H. trivolvis became infected and Physa heterostropha did not (Fried, 1985, Proceedings of the Pennsylvania Academy of Science 59: 27-28). In this study, that procedure was repeated and extended to include other species of laboratory-raised pulmonate snails. Miracidia were derived from E. revolutum adults raised in hamsters (Franco et al., 1986, Journal of Parasitology 72: 142-147). The uteri of worms were teased, eggs were embryonated in tap water at 22-24 C for 2-3 wk, and miracidia were used within 4 hr of emergence from eggs. Most snails were exposed individually in multiwell chambers (Anderson and Fried, 1987, Journal of Parasitology 73: 49-54) for 4 hr to 10 miracidia per snail. In some trials with Helisoma trivolvis (Pennsylvania strain), snails were also exposed to either 1, 5, or 20 miracidia/snail (see Table I). Following exposure, snails were placed in 10-20/1,000 ml of aerated artificial spring water in glass jars and maintained at 22-24 C under diffuse overhead fluorescent light for 12 hr/day and fed ad libitum on boiled lettuce. They were necropsied 4-6 wk postexposure. Laboratory-raised, helminth-free Helisoma trivolvis (PA strain), Physa heterostropha (PA strain), and Biomphalaria glabrata (Puerto Rican strain) were raised in the laboratory from eggs (Anderson and Fried, 1987, loc. cit.), in addition to a highly inbred strain of Helisoma trivolvis (Colorado strain) maintained in laboratory culture since the mid 1960's (Kater, 1974, American Zoologist 14: 1017-1036). Helisoma trivolvis (PA strain) is a first intermediate host of E. revolutum (Fried, 1985, loc. cit.). To assure the viability ofE. revolutum miracidia, H. trivolvis (PA strain) was always exposed to miracidia as a positive control for this experiment. The shell diameters of snails used in this study were: 3-10 mm for P. heterostropha; 3-16 mm for B. glabrata and Helisoma trivolvis (PA strain); and 8-12 mm for H. trivolvis (Colorado strain). A total of 183 H. trivolvis (PA) was exposed to miracidia; another 100 H. trivolvis (PA) were left as controls and were not exposed to miracidia.