A selected number of 5 villages near Lake Victoria shown to maintain very high levels of infection with S. mansoni following at least three rounds of annual praziquantel chemotherapy will be compared with 5 villages where infection rates have been much more responsive to similar levels of treatment, with respect to the following general considerations and questions:

1) What is the general situation for each village with respect to proximity of water bodies where intensive human contact occurs?

2) For each village, what is the role of each major habitat in transmission, as assessed by three separate techniques: water filtration; use of sentinel mice; and standard snail survey techniques?