Control of schistosomiasis: The Puerto Rican experience

Following the discovery of Schistosomiusis mansoni on the island of Puerto Rico in 1904, studies based on fecal samples were done to determine the extent of the problem. By 1953 a Bilharzia Control Unit had been established within the Puerto Rico Department of Health and a snail control project was instituted in an attempt to disrupt the transmission cycle of the schistosome parasite. Considerable attention was given to the study of the ecologies of transmission foci in order to better understand the interrelationships among people, snails, and schistosomes. During the 1960s the useful but limited method of fecal sampling was replaced by the intradermal skin test using schistosome antigen. Three surveys using the intradermal test had been carried out by 1976. and they revealed a changing pattern in the prevalence of schistosomiasis on the island. The various control programs and social factors responsible for this shift are assessed in terms of their contributions to the total program of control. Unlike many other control programs, the Puerto Rican effort has not stressed chemotherapy but rather has relied on measures such as snail control, improvements in water supplies, and better sanitation. Since the initial intradermal test of 1963, prevalence of schistosomiasis has declined from 12% to approximately 5% in 1976. While undeniably successful, the continuance of snail control as a major factor in the total control program is questionable, as cost analyses indicate that new chemotherapeutic measures might do the job more quickly and cheaply than snail control.