Tropical Disease Section, Ecological Investigations Program, National Communicable Disease Center, Bureau of Disease Prevention and Environmental Control, U.S. Public Health Service, and Puerto Rico Department of Health, San Juan, Puerto Rico
The transmission of schistosomiasis in Vieques Island was controlled in 7 years by a program that combined control of snails and chemotherapy in infected persons. The control program began in 1954 when the prevalence of schistosomiasis was 6.7% among 6-year-old children. By 1958 transmission had stopped among children in the schools at high risk, and by 1959 the prevalence was down to zero. Ova were found in the stools of only two 6-year-old children in the ensuing 8 years, the last one in 1962. Prevalence in older children showed a similar decline. Although the prevalence in other parts of Puerto Rico was also declining, in Vieques the prevalence went to zero and remained there.
The meaning of the control of schistosomiasis in Vieques Island is twofold: it verifies the theoretical analysis by MacDonald that chemotherapy and control of snails will produce a rapid drop in transmission,7 and it shows that it is not necessary to eradicate the snails in order to interrupt transmission. Small numbers of snails have persisted in Vieques despite 12 years of concerted effort at their eradication.
The control of schistosomiasis in Vieques was a small accomplishment on a small island, aided by many naturally occurring factors. It represents no scientific or engineering feat, but the steady, conscientious application of simple methods, year in and year out. As such, this pilot project is an encouraging indication of the feasibility of schistosomiasis control for all of Puerto Rico.