Possible Snail Hosts of Human Schistosomes in the United States

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Abstract
Sexually mature stages of Schisto-soma mansoni, S. haematobium and S.japonicum were maintained in experimental animals and their larval stages in the snails which serve as natural hosts. During a 3-yr. study, conducted under the auspices of the O. S. R. D. and the Office of the Surgeon General of the U. S. Army, eggs of the 3 spp. of blood flukes were collected and the miracidia were placed in suitable containers with native N. Amer. snails, collected in the field or raised in the laboratory. Exposures were both individually and en mass. Representatives of 22 snail spp. were exposed to miracidia of S. mansoni, of 25 spp. to S. haematobium, and of 25 spp. to S. japonicum. The miracidia were attracted in greater or lesser degree to several spp. of snails, and the larvae attached and penetrated in most of the snails tested. In several instances the miracidia, after penetration, lost their cilia and became primary sporocysts. In a few instances the germinal cells developed into germ balls of the next generation, but no mature cercariae were obtained. Repeated attempts to infect specimens of Tropicorbis havanen-sis were unsuccessful, although Cram, Jones and Wright have proved that other specimens can transmit the parasite. Accordingly, failure to infect a sample of any species does not thereby demonstrate that the species is incapable of serving as an intermediate host.