Effect of annual mass administration of diethylcarbamazine and albendazole on bancroftian filariasis in five villages in south India

Annual mass drug administration (MDA) is the recommended strategy for lymphatic filariasis (LF) elimination. We assessed the effect of six rounds of mass administration of diethylcarbamazine (DEC) and albendazole (ALB) on microfilaria (Mf) prevalence and intensity and vector infection and infectivity rates and circulating filarial antigenaemia (CFA) in a group of five villages in south India, endemic for Culex-transmitted bancroftian filariasis. During different rounds of MDA, 60-70% of the eligible population (>15 kg body weight) was treated. The MDA reduced the Mf prevalence from 8.10% (CI 6.18-10.01) to 1.01% (CI 0.31-1.71) (P<0.05) and geometric mean intensity of Mf from 0.31 (CI 0.22-0.40) to 0.02 (CI 0.00-0.04) (P<0.05), equivalent to a fall of 86% and 94% respectively. The vector infection and infectivity rates declined from 13.11% (CI 11.52-14.70) to 0.78% (CI 0.16-1.40) (P<0.05) and 1.04% (CI 0.56-1.52) to 0.13% (CI 0.00-0.39) (P<0.05), respectively. Four out of the five villages recorded <0.5% Mf prevalence and 0% vector infection rate. Circulating filarial antigenaemia (CFA) fell by 86% in the total population and 100% in 1-10 year old children. One of the five villages, which showed the highest baseline vector infection rate, showed >1.0% Mf rate. The results suggest that six rounds of mass administration of DEC and ALB, with 60-70% treatment coverage, is likely to achieve total interruption of transmission and elimination of LF in the majority of villages.