Prospects for elimination of bancroftian filariasis by mass drug treatment in Pondicherry, India: A simulation study

LYMFASIM, a microsimulation model for transmission and control of lymphatic filariasis, was used to simulate the effects of mass treatment, in order to estimate the number of treatment rounds necessary to achieve elimination. Simulations were performed for a community that represented Pondicherry, India, and that had an average precontrol microfilariae (MF) prevalence of 8.5%. When ivermectin was used, 8 yearly treatment rounds with 65% population coverage gave a 99% probability of elimination. The number of treatment rounds necessary to achieve elimination depended to a large extent on coverage, drug efficacy, and endemicity level. Changing the interval between treatment rounds mainly influenced the duration of control, not the number of treatment rounds necessary to achieve elimination. Results hardly changed with alternative assumptions regarding the type of immune mechanism. The potential impact of mass treatment with a combination of diethylcarbamazine and albendazole is shown under different assumptions regarding its efficacy. Human migration and drug resistance were not considered. Results cannot be directly generalized to areas with different vector or epidemiological characteristics. In conclusion, the prospects for elimination of bancroftian filariasis by mass treatment in Pondicherry seem good, provided that the level of population coverage is sufficiently high.