Negative conversion of COP (circumoval precipitation) reactions after selective mass chemotherapy on schistosomiasis japonica with praziquantel in Bohol, Philippines.

For the longitudinal survey of human schistosomiasis japonica in the villages of Sto. Tomas and San Vicente in the province of Bohol, Philippines, the circumoval precipitin (COP) test was used for case detection. Plasma collected by finger prick from the community people and lyophilized eggs of Schistosoma japonicum were used for the assay. Degree of precipitation at type 2 or 3 of Yokogawa et al. [1] was considered as positive. Selective mass chemotherapy with praziquantel was given to the patients including cases with only positive COP reactions. San Vicente and Sto. Tomas villages were examined in 1984 and 1982, respectively and followed up in 1986. Positive COP reactions were converted to negative in 82.1% or 55 out of 67 cases treated in 1984 and 1985 at San Vicente. Similarly, negative conversion was observed in 75.4% or 43 out of 57 cases treated in 1981 and 1982 at Sto. Tomas. The cases with persistent positive COP reaction after treatment were considered as incomplete cure or reinfection. The concentrated distribution of positive cases around the habitat of Oncomelania snails was observed at San Vicente where the prevalence of COP positives declined from 22.2% to 14.0% in 2 years. These results suggest that in the area with selective mass chemotherapy on schistosomiasis japonica, COP reactions of treated cases are converted to negative at high proportions in 2 years, and the positives detected by subsequent survey after 2 years are considered mostly as new infections or reinfections.