Impact of 10 years of diethylcarbamazine and ivermectin mass administration on infection and transmission of lymphatic filariasis

The potential of repeated mass administration of diethylcarbamazine (DEC) and ivermectin to eliminate lymphatic filariasis has been examined in a study implemented in 10 villages with a population of 18 415 in south India. During ten rounds of mass drug administration, 49-84% of the eligible population received treatment in different villages. Ten rounds of mass administration of DEC alone reduced the microfilaria (mf) prevalence and intensity by 93% and 97%, respectively, and the vector infection and infectivity rates by 91% and 89%, respectively. The corresponding figures with nine rounds of administration of ivermectin alone were 83%, 90%, 89% and 79%. Out of five villages in each treatment arm, the mf rate declined to ≤1% in four villages in the DEC arm and two villages in the ivermectin arm. No mosquitoes with infective-stage larvae were found in three of five villages in the DEC arm and two of five villages in the ivermectin arm. None of the children (n = 130) were found to be positive for mf in either treatment arm. None of the 40 sampled children were found to be positive for circulating filarial antigenaemia in villages with lower endemicity in the DEC arm. The results suggest that ten rounds of DEC mass administration have the potential to interrupt transmission of infection in the majority of communities. The outcome was relatively less remarkable with ivermectin.