EFFECT OF 2 SUCCESSIVE ANNUAL TREATMENTS WITH SINGLE DOSES OF IVERMECTIN ON MICROFILAREMIA DUE TO WUCHERERIA-BANCROFTI VAR PACIFICA

Between 1986 and 1988 a single-blind, doseranging study was carried out in French Polynesia to determine the efficacy and tolerability of single 50, 100, 150 and 200-mu-g/kg doses of ivermectin in Wuchereria bancrofti carriers. Forty male microfilariae (mf) carriers between 18 and 50 years of age, in whom mf density was greater-than-or-equal-to 20 mf/ml, were treated twice at a one-year interval. Twelve months after the second treatment, in carriers who were given a dose greater-than-or-equal-to 100-mu-g/kg, mean mf density was 4-7% of the initial pretreatment mf density. Therefore, several successive annual treatments with single doses greater-than-or-equal-to 100-mu-g/kg of ivermectin should result in reducing mf densities to a very low level. Nevertheless, at 9 months after the second treatment, residual parasitaemia ranged from 1 to 2182 mf/ml (median 85) in 30 patients. Finally, in patients with pretreatment mf counts less-than-or-equal-to 150 mf/ml, mean mf density was 2.8 and 8.9 mf/ml, respectively, during the 2 six-month periods following treatment, while in patients with pretreatment mf densities > 150 mf/ml (median 1500) it was 92.3 and 334.1 mf/ml during the same periods. These results suggest that, when implementing filariasis control programmes, the best strategy might be administration of several treatments with a single dose of ivermectin every 6 months to the entire population, at least in French Polynesia. Afterwards, when mf densities had been reduced to a relatively low level (100-150 mf/ml), annual treatments could be considered.