Diethylcarbamazine in the control of bancroftian filariasis in the Ok Tedi area of Papua New Guinea: phase 2--annual single-dose treatment.

The Phase 1 semiannual single-dose 6 mg/kg diethylcarbamazine (DEC) treatment program demonstrated a significant reduction for Wuchereria bancrofti in the Ok Tedi area of Western Province, Papua New Guinea. The rate of detectable microfilaraemia was effectively reduced from 39% to 11% and mean microfilarial (mf) densities from 79mf/20 microliters to 19mf/20 microliters. The Phase 2 annual single-dose treatment of 6mg/kg DEC not only maintained the gains made during Phase 1 but reduced the microfilaraemia rate to less than 5% by 1990, with mf densities remaining stable at less than 20mf/20 microliters, amongst all participating villagers screened within the 5 original villages. The annual treatment program was expanded into 7 remote villages not subject to any form of active vector control. The microfilaraemia rate in these villages declined from 41% before treatment to 17% after only two annual administrations of 6mg/kg DEC, and mf blood densities were reduced from 71mf/20 microliters to 20mf/20 microliters. As was observed in the 5 original villages participating in the program, a significant reduction in splenomegaly associated with the DEC treatment was reported for the 7 villages in the expanded program during Phase 2; enlarged spleen rates were reduced from 50% (1986) to 32% (1990) and from 76% (1988) to 48% (1990), respectively. Malaria rates on the other hand increased slightly or remained stable. Malaria infections associated with W. bancrofti (mixed parasite infections) stimulated a greater splenic response than either parasite detected on its own.