Mass chemoprophylaxis of lymphatic filariasis with a single dose of ivermectin in a Polynesian community with a high Wuchereria bancrofti infection rate

Abstract
In April 1991 supervised mass prophylaxis of lymphatic filariasis with a single dose of ivermectin, 100 μg/kg, was carried out in a Polynesian village with a high infection rate of Wuchereria bancrofti in humans and active transmission by the vector mosquito, Aedes polynesiensis. Of 876 inhabitants aged 3 years or more (pregnant women excluded), 864 (98·6%) were treated. Simultaneously, venous blood samples were collected from 577 (97·5%) of the 595 inhabitants aged 15 years or more, of whom 122 (21·4%) were found to be microfilaria (mf) carriers (86 males and 36 females). The geometric mean microfilariae (GMM) count was 358·7 mf/ml for the whole group, 387 mf/ml for males (range 1–8160 mf/ml) and 280 mf/ml for females (range 1–7769 mf/ml). Following treatment, 33 (3·8%) of the 864 persons treated experienced some adverse reactions (21 with grade 1 and 12 with grade 2). Of the 33 with reactions, 29 were among the 122 (23·8%) mf carriers and 4 among the 831 (0·5%) non-microfilaraemic persons. Six months later, 123 (21·1%) of 584 inhabitants sampled were microfilaraemic: the GMM count for the whole group was 106 mf/ml (1–8177), with 29 mf/ml (1—3740) in 35 female and 177 mf/ml (1–8177) in 88 male carriers. Of these 123, 15 (whose GMM count was 4·5 mf/ml; range 1–204) were amicrofilaraemic 6 months before, and 19 had a microfilaraemia level higher than that 6 months earlier, before treatment. 117 of the 122 carriers identified in April were resampled: comparison of their GMM counts before and 6 months after mass treatment indicated that treatment with a single dose of 100 μg/kg ivermectin resulted in a reduction of microfilaraemia by 69%.