Periodic mass treatment with diethylcarbamazine for the control of filariasis in American Samoa.

Filariasis surveys made during 1962-63 in 5 villages in American Samoa among persons over 5 years of age gave an elephantiasis rate of 3.4%, a microfilarial rate of 26% and a median microfilarial rate (MfD(50)) of 29. These rates were somewhat higher than those found in surveys made in the same villages among villagers of the same ages some 20 years previously. A mass treatment programme with diethylcarbamazine was then decided on.Preliminary treatment with a single total regimen of 72 mg of the drug per kg of body weight, given in 12 doses of 6 mg/kg, was administered in several villages over a period of 6 months. Among villagers of all ages at the end of 3 years, the microfilarial rate was 7.3% and the MfD(50) value was 2. These results appeared to be inadequate for a successful control programme and a periodic mass treatment project of 2 or more regimens of 72 mg/kg to be administered every 2 years was instituted on the Island of Tutuila, to be continued until considered no longer necessary.Surveys made 2 years after the second mass treatment in the villages of Amouli, Amanave, Onenoa, Tula, Alao, Utumea and Alofau, in which 1407 persons were examined, showed that 3 villages were negative for microfilariae, that the average microfilarial rate in all 7 villages was 0.4% and that the MfD(50) was 1. These villages were also negative in intensive mosquito surveys for infective-stage larvae of Wuchereria bancrofti. It is suggested that interruption of transmission has been observed in the 3 villages negative for both microfilariae and infective-stage larvae and that, if favourable surveys continue, eradication programmes should be established.