Epidemiological importance of COP reactions in areas lightly infested with Schistosoma japonicum in the Philippines.

Abstract

Dwellers in 6 villages in Talibon and Trinidad in Bohol, Philippines with an approximate population of 5, 740 were examined for schistosomiasis japonica by stool examination and circumoval precipitin (COP) test during the period from 1981 to 1984. Eggs were positive in 3.5% of 4, 117 examinees, whereas COP positives were 9.8% in 4, 094 examinees. Since prevalence of egg positives among COP positives increased from 24.4 and 24.0% to 79.1 and 48.1%, in 2 villages after repeated stool examinations, respectively, COP reactions by standardized method seem to indicate the actual infection of individuals. Among 6 villages, the prevalence did not vary much between 1.4% to 6.9% by a single stool examination while there was greater variation between 3.2% and 22.2% by COP test. Two villages, San Vicente and Sto. Tomas, were identified as the area of highest risk. At San Vicente where no snail colony had previously been found; a new snail colony was first identified at Apao Palawan Swamp in July 1984. The distribution of households of infected persons showing strong COP reactions led to the suspicion of presence and the eventual discovery of the snail colonies in the area.