Microfilariae recurrence in Polynesian Wuchereria bancrofti carriers treated with repeated single doses of 100 micrograms/kg of ivermectin.

Forty-six Polynesian carriers of Wuchereria bancrofti were treated with 3 successive single doses of ivermectin, 100 micrograms/kg, given every 6 months. Immediate microfilaricidal activity of ivermectin was excellent in all carriers, since residual mean microfilaraemia levels, 2 d after each of the 3 treatments, were less than 1% of pretreatment levels. Before initial treatment, geometric mean microfilaraemia was 500 microfilaria (mf)/ml for the whole group (range 21-6398 mf/ml); 6 months after each successive treatment it was 197, 108 and 87 mg/ml, respectively, 39.4, 21.6 and 17.4% of the pre-initial treatment level. By considering the mean percentage recurrent level at 6 months after the 3rd treatment (36.8%) as a threshold, it was possible to classify the carriers into 2 groups: 17 in whom the percentage recurrent level was > 36.8% and who were considered as 'fast repopulating' individuals, and the remaining 29 who were considered as 'slow repopulating' individuals. In the latter group, 6 months after each of the 3 treatments, the recurrent microfilaremia levels were 22.7%, 8.0% and 4.9% of the pre-initial treatment level, respectively, while they were 95.1%, > 100% and > 100% in the former. The constant recurrence of mf suggests that ivermectin, at a dosage of 100 micrograms/kg, had no effect on adult worms in 'fast repopulating' individuals, whereas the progressive lessening in recurrence of mf suggests some activity (sterilizing or killing) of ivermectin on W. bancrofti macrofilariae in 'slow repopulating' individuals.(ABSTRACT TRUNCATED AT 250 WORDS)