Repeated mass treatment of schistosomiasis mansoni: experience in hyperendemic areas of Brazil. II. Micro-level evaluation of results.

As shown by a recent survey in northeast Brazil, an overall (macro-level) assessment of control campaigns for schistosomiasis mansoni will tend to ignore localized variations in endemicity, thus resulting in misleading information. Evaluation on a micro-level, on the other hand, allows the identification of individuals who, despite repeated courses of chemotherapy, continue to present substantial reinfection rates. Such cases occur in a definite spatial pattern, which in turn points to the localization of residual foci of transmission. It is believed that in the absence of wide-reaching social investments the control of schistosomiasis by means of mass treatment will not be successful, unless a policy of targeted action, both in chemotherapy as well as snail control, is adopted. Obviously, the search for these reinfection clusters will require the development of sampling techniques suitable for wide-scale use.