Annual single-dose diethylcarbamazine plus ivermectin for control of bancroftian filariasis: comparative efficacy with and without vector control.

Two intervention strategies for the control of bancroftian filariasis were compared in rural villages of southern India: annual mass treatment with single-dose diethylcarbamazine plus ivermectin, either on its own or combined with vector control. Vector control, based on the use of polystyrene beads and larvivorous fishes in the major breeding sites of Culex quinquefasciatus, brought about a drastic and sustained reduction in vector density and man-biting rates. After the first round of treatment, chemotherapy alone brought about a 60% drop in the annual transmission potential (ATP) whereas the integrated strategy reduced ATP by 96% (P < 0.05). After two annual rounds of treatment, the reduction in ATP was similar for both strategies (91%-96%), with the prevalences of microfilaraemia reduced by 88%-92%. However, when drug pressure was removed in the third and final year of the study, transmission was resumed in the absence of vector control whereas no infective female mosquitoes were detected in the villages with vector control. Vector control, though obviously not cost-effective in the short term, could play an important role in an integrated programme, by preventing re-establishment of transmission after chemotherapy is completed.