Ecological control of the snail host of Schistosoma japonicum in the Philippines.

Ecological measures for the control of Oncomelania quadrasi have been in effect over a large part of the municipality of Palo, Leyte, Philippines, since the end of 1956. These measures involve draining, ponding or filling snail habitats. The results show that complete eradication of the snails is possible where complete control of water is achieved; less radical measures always leave a greater or smaller fraction of the snail population.In the area where control was planned, reductions of 50%, 80% and 85.7% were observed by mid-year 1957, 1958 and 1959 respectively. The figures include four large snail populations not subjected to control measures, but within the planned area; if these are omitted, 95% of the snails had been eliminated by July 1959. The measures used are expensive, but result in benefits in land reclamation and improved land use sufficient to offset the high cost.