Mass DEC chemotherapy for control of bancroftian filariasis: comparative efficacy of four strategies two years after start of treatment.

The efficacy of 4 strategies for control of bancroftian filariasis using mass diethylcarbamazine (DEC) chemotherapy was evaluated and compared in 4 endemic communities in Tanzania 2 years after the start of treatment. The strategies used were the standard 12 d treatment (strategy I), a semi-annual single dose treatment (strategy II), a monthly low dose treatment (strategy III), and DEC medicated salt (strategy IV). Treatment took place during the first study year, and no treatment was given during the second year. Among individuals who were microfilaraemic before treatment, the microfilaria (mf) clearance rates were 41.5%, 75.0%, 84.0% and 89.1%, and the pre-treatment mf geometric mean intensities (GMIs) were reduced by 97.1%, 98.9%, 99.8% and 99.8%, for strategies I, II, III and IV, respectively, 2 years after starting treatment. Statistical analysis indicated that strategies III and IV were equally effective, and superior in clearing microfilaraemias and in reducing mf GMIs compared to strategies I and II; strategy II was significantly more effective than strategy I. The rate of occurrence of new cases of microfilaraemia among individuals who were amicrofilaraemic during the pre-treatment surveys was negligible over the study period in all communities. In all the communities combined, 66.6% of males presenting hydrocele before treatment, and 61.5% of individuals presenting elephantiasis before treatment, showed improvements in these conditions 2 years after the start of treatment, either as a reduction in size or complete disappearance.