Placebo-controlled community trial of four cycles of single-dose diethylcarbamazine or ivermectin against Wuchereria bancrofti infection and transmission in India

A double-blind placebo-controlled trial was carried out in 1994-98 to compa re the effects of 4 cycles of single-dose diethylcarbamazine (DEC) or iverm ectin on prevalence and geometric mean intensity (GMI) of microfilaraemia i n the human population, infection rates in the vector population, and trans mission intensity of Culex-transmitted Wuchereria bancrofti in rural areas in Tamil Nadu state, south India. Fifteen villages (population similar to 2 6 800) were included in the study: 5 villages each were randomly assigned t o community-wide treatment with DEC or ivermectin or placebo. People over 1 4 kg bodyweight received DEC 6 mg/kg, ivermectin 400 mug/kg or a placebo, a ll identically packaged. After 2 cycles of treatment at a 6-month interval, the code was broken and the study continued as an open trial, with third a nd fourth cycles of treatment at a 12-month interval; 54-77% of eligible pe ople (20 872) received treatment during the 4 cycles. Microfilaraemia preva lence and GMI fell by 48% and 65% with DEC and 60% and 80% with ivermectin respectively after 4 cycles of treatment. There was no change in the incide nce of acute adenolymphangitis. Infection in resting mosquitoes fell signif icantly in all arms: 82%, 78% and 42% in the ivermectin, DEC and placebo ar m, respectively. Landing mosquitoes also showed the same trend. The decline in infectivity was significant for resting (P < 0.05) and landing mosquito es (P < 0.05) with ivermectin and DEC (P < 0.05), and for neither in the pl acebo group (P > 0.05). Transmission intensity was reduced by 68% with iver mectin and 63% with DEC. Transmission was apparently interrupted in 1 villa ge with ivermectin, but infected resting mosquitoes were consistently found in this village. Single-dose community-level treatment with DEC or ivermec tin is effective in reducing W. bancrofti infection in humans and mosquitoe s, and may result in total interruption of transmission after several years of control. There is an immediate need to define the role of vector, paras ite and community factors that influence the elimination of lymphatic filar iasis, particularly the duration of treatment vis-a-vis efficacy of drugs, treatment compliance and efficiency of vectors.