Effect of mass treatment of a human population with ivermectin on transmission of Onchocerca volvulus by Simulium yahense in Liberia, West Africa.

The impact of mass treatment with ivermectin on the intensity of Onchocerca volvulus transmission by the black fly (Simulium yahense) was evaluated on the Liberian Agricultural Company rubber plantation in Liberia, West Africa. The adult pre-treatment prevalence of onchocerciasis was greater than 80%, and the average intensity of infection was 5.35 mf/mg of skin. The drug was administered at 2 annual intervals, reaching 58-60% of the approximately 14,000 people living in 73 camps. Landing/biting catches of black flies made in central and peripheral plantation zones indicated similar fly activity before and after ivermectin treatment (man hr index of 2.1 and 2.4 within the plantation, and 10 and 10.9 outside the plantation, respectively). The number of infected flies with developing larvae (L1, L2, L3 stages) of O. volvulus in treated areas was reduced by 93.4-95%; the number of infective flies with L3 larvae was reduced by 81.7-89.3%. Parasite loads of infected (L1, L2) and infective flies (L3 stages only) outside the plantation also decreased by 86.8% and 80%, respectively. Monthly transmission potential (MTP) showed a similar decrease: from 22.9 to 5.8 (74.6% reduction) in the treated area, and from 210 to 158.8 (24.4% reduction) in untreated areas. Mass treatment with ivermectin efficiently controlled, and at least temporarily interrupted, transmission of Onchocerca volvulus by black fly vectors.

Viability of adult Onchocerca volvulus after six 2-weekly doses of ivermectin.

Ivermectin is a safe, effective microfilaricide and microfilarial suppressant for Onchocerca volvulus; but in single doses of 100-200 micrograms/kg body weight it has no macrofilaricidal action. The present trial aimed to determine whether 6 doses of 100 micrograms/kg ivermectin, given at 2-week intervals, would kill the adult worms. Eighty-two nodules from 28 otherwise healthy adult male Liberian patients treated with this ivermectin schedule, and 102 nodules from a similar group of 25 control patients, were removed four months after the last dose of ivermectin. They were coded and assessed in a masked fashion either by routine histology or by examination of whole worms extracted from the nodules after collagenase digestion. The drug had no visible effect on adult male worms. More adult female worms were assessed as moribund or dead in the ivermectin-treated group than in the control group (for the collagenase digests P = 0.09; for the histological assessment P = 0.47). The data suggest that repeated dosage with ivermectin may lead to a slow attrition of some female worms and this possibility should be investigated in patients receiving regular doses every 3, 6 or 12 months as part of onchocerciasis control programmes.

Community-based treatment of onchocerciasis with ivermectin: acceptability and early adverse reactions.

A study of community-based treatment of onchocerciasis with ivermectin was undertaken in a rain forest area of Liberia to investigate the possible occurrence of serious adverse effects. The total population was 13,704, the microfilarial load was 5.35 mf/mg skin, and the prevalence of Onchocerca volvulus infection was 50% at 9 years of age and over 80% among those aged 15 years and older. Certain groups (like pregnant women and young children) were excluded from treatment. Out of the 7956 people eligible for treatment, 7699 (97%) accepted the ivermectin. Data on possible adverse reactions were collected by four different methods, including systematic house-by-house follow-up visits three days after treatment, biweekly population surveillance, and monitoring of both mobile clinic records and hospital records. No severe adverse reactions were noted, and no deaths could be related to ivermectin treatment; only 1.3% of the persons treated had a moderate adverse reaction of the Mazzotti type, presumably related to the killing of microfilariae. The study showed good acceptance by the population, and that mass treatment campaigns with ivermectin are feasible.

Community-based treatment of onchocersiasis with ivermectin: acceptability and early adverse reactions

A study of community-based treatment of onchocerciasis with invermectin was undertaken in a rain forest area of Liberia to investigate the possible occurrence of serious adverse effects. The total population was 13,704, the microfilarial load was 5.35 mf/mg skin, and the prevalence of Onchocerca volvulus infection was 50 percent at 9 years of age and over 80 percent among those aged 15 years and older. Certain groups (like pregnant women and young children) were excluded from treatment

Out of the 7,956 people eligible for treatment, 7,699 (97 percent) accepted the ivermectin. Data on possible adverse reactions were collected by four different methods, including systematic house-by-house follow-up vistis three days after treatment, biweekly population surveillance, and monitoring of both mobile clinic records and hospital records. No severe adverse reactions were noted, and no deaths could be related to ivermectin treatment; only 1.3 percent of the persons treated had a moderate adverse reaction of the Mazzotti type, presumably related to the killing of microfilariae. The study showed good acceptance by the population, and that mass treatment campaigns with invermectin are feasible(AU)