A note on drug trials in schistosomiasis.

In schistosomiasis, if the subjects of drug trials are in contact with potentially contaminated water, then differences in the chemotherapeutic response to the same dose of a drug given in the same endemic area in different seasons, may be related to different levels of transmission. Because a reduction in egg excretion may occur from causes other than chemotherapy, moderate antischistosomal activity of a drug cannot be concluded in the absence of a control group.