During 1953 a single fecal sample from each of over 10,000 Puerto Rican school children was examined for helminth eggs, especially those of S. mansoni. The following average percentage rates of infection were found: S. mansoni, 10.0; hookworm (Necator and Ancylostoma), 17.1; Trichuris trichiura, 92.6; Ascaris lumbricoides, 20.3; and Strongyloides stercoralis, 0.4. The incidence of S. mansoni in boys and girls was 12.5 and 8.1 per cent, respectively. This difference was significant at odds greater than 99:1. A high degree of correlation (r = 0.89) was found between the age of the boys and their rate of S. mansoni infection, while with the girls, these factors were not correlated (r = 0.38).
In general, the abundance of the snail vector (Australorbis glabratus) was related directly to the incidence of human schistosomiasis. There was little or no agreement between S. mansoni infection rates in snails and those in human beings at a given time in a particular locality. The epidemiological aspects of these findings are discussed in the light of results obtained from a study of human beings, snails and S. mansoni infections in three stream communities and from other studies in selected regions in Puerto Rico.
Present address: Department of Biology, Mercer University, Macon, Georgia.
Present address: Department of Entomology and Limnology, Cornell University, Ithaca, New York.
Commonwealth of Puerto Rico Department of Health, San Juan, Puerto Rico.