Schistosomiasis control in Puerto Rico: twenty-five years of operational experience

A program to control schistosomiasis in Puerto Rico was initiated in 1953, using limited chemotherapy and snail control by environmental, biological and chemical means. At the same time, extensive programs of water supply, health education, and free latrine distribution were underway throughout the island. The impact of the program was evaluated initially by examinations of fecal samples from first-grade children until 1966, and subsequently by island-wide surveys using adult worm antigen for skin test on fifth-graders in 1963, 1969, and 1976. There was a decrease in the proportion of children reacting positively to the skin test from 24% in 1963 to 5% in 1976. The decrease in the proportion of positive skin test reactions was one and a half times as great in the area under snail control as in the rest of the endemic area, and most of the decrease outside the snail control program was due to improved water supply. Calibration tests indicated a decrease in prevalence among the entire population, if determined by multiple fecal exams, from 15% in 1963 to less than 4% in 1976. Thus the estimated number of persons passing eggs in Puerto Rico was about 100,000 in 1976, in a population of 3 million. The cost of snail control was minimized by emphasizing environmental and biological methods, showing that the disease can be controlled on a large scale with simple techniques. Eradication of the parasite from Puerto Rico is quite likely in the next few years with the advent of the new drug, oxamniquine, and would be a cheaper strategy than continued snail control.