LONG-TERM EFFECT OF MASS DIETHYLCARBAMAZINE CHEMOTHERAPY ON BANCROFTIAN FILARIASIS - RESULTS AT 4 YEARS AFTER START OF TREATMENT

The long-term effect of 4 strategies for control of bancroftian filari asis using mass diethylcarbamazine (DEC) chemotherapy was assessed and compared in 4 endemic communities in Tanzania over a period of 4 year s. The strategies were the standard 12 d treatment (strategy I), semi- annual single dose treatment (strategy II), monthly low dose treatment (strategy III), and DEC-medicated salt treatment (strategy IV). Treat ment was given only during the first year. All strategies resulted in considerable reductions in microfilaraemia, with maximum effects occur ring 1-2 years after start of treatment. At 2 years, the greatest redu ctions were seen for strategies III and IV, followed by strategy II an d finally strategy I. The overall performance of the 4 strategies eval uated over the 4 years period followed the same sequence. Between the 2 years and 4 years follow-up surveys, a significant increase in micro filarial (mf) burden occurred in all 4 communities, but the mf geometr ic mean intensities (GMI) remained low. Thus, in individuals who were microfilaraemic before treatment, the rates of microfilaraemia were 66 %, 44%, 34% and 43%, and the mf GMIs were 6.8%, 3.3%, 0.5% and 0.7%, o f pre-treatment level, 4 years after start of treatment with strategie s I, II, III and IV, respectively. Most individuals who developed micr ofilaraemia between the 2 years and 4 years follow-up surveys had been microfilaraemic before the start of treatment. Hence, the rate of dev elopment of microfilaraemia was much higher (18 times on average in th e 4 communities) among those who were microfilaraemic before treatment than among those who were amicrofilaraemic. The long-lasting effect o f treatment adds a promising potential to the use of mass DEC chemothe rapy for the control of bancroftian filariasis.