MOLLUSKS AND MEDICINE — ABBOTT 333 



tions do not necessarily forecast what may happen in nature. Schis- 

 tosomiasis is unknown in Cuba where the snail is rather common, and 

 where undoubtedly infected visitors have given the disease every op- 

 portunity of becoming established. A number of parasitologists be- 

 lieve that the slave trade, with its accompanying cases of the two kinds 

 of African schistosomiasis, has served as a great natural "experiment" 

 in which it was clearly demonstrated that neither of the diseases were 

 able to establish themselves in this country. It is probable that slaves 

 were able to introduce Manson's disease into Puerto Rico, the Lesser 

 Antilles, and northern South America because of the presence of a suit- 

 able snail host. A similar "experiment" occurred in the Canal Zone 

 during World War I where a few infected Puerto Rican troops were 

 stationed. The disease did not establish itself in that area, nor have 

 mollusk surveys brought to light species of known carriers. 



Research on the potential American snail carriers of Oriental schis- 

 tosomiasis has been intensified recently by the promising early experi- 

 ment of Dr. Horace Stunkard at Princeton. He has found that the 

 Pomatiopsis snail can be infected by the Oriental disease, but has been 

 unable, so far, to have the larval worm complete its growth. Present 

 experiments now being continued at the National Institute of Health 

 may meet with further success. The Pomatiopsis snail, already well 

 known as a carrier of animal lung flukes in this country, is extremely 

 close in its morphology and amphibious habits to the Oriental schisto- 

 somiasis carrier. In fact, it has been dubbed the "Oncomelania snail 

 of North America." Its distribution, as shown by the accompanying 

 map, is limited to the central regions of the United States except for a 

 minor area of dispersal along the central portion of the Atlantic 

 coastal plain. 



By far the weakest link in our public-health defense is in future 

 accidental introductions of known snail carriers from foreign coun- 

 tries. A number of slugs and other garden pests, including the giant 

 African land snail, have already found their way to our shores. No 

 disease carriers have been found in the United States as yet. The 

 possibility of this is not too remote, as is demonstrated by the recent 

 introduction and establishment of a Brazilian race of the Australorbid 

 snail carrier of Manson's disease on Luzon Island, Philippines. It 

 may be only a matter of time before the disease finds its way from 

 Africa or the West Indies to the Philippines through the agency of 

 some infected traveler. The importation of living snails into this coun- 

 try IS subject to the fine-toothed combings of our plant quarantine 

 and control agents, but this is not necessarily a perfect screen. Once 

 here, the Oncomelania snail has ample room for spreading, and would 

 probably follow much the same distribution of the Pomatiopsis snail. 

 As long as the accidental introduction is discovered within a year or 

 two, no harm will have been done. Newly introduced species usually 



