Onchocerca Volvulus: Effects of Annual Treatment with Ivermectin on Prevalence and of infection

Abstract

Vector control is practical and effective in only a circumscribed region of West Africa. As an alternative to vector control, chemotherapy – based control has been revolutionized by the finding that ivermectin, a novel semi synthetic macrocyclic lactone, is safe and acceptable for mass distribution at the community level. In this study, the effect of ivermectin treatment was evaluated by comparing the pre- and post-treatment intervention prevalence and intensity, over a 3 year period. The pre-intervention prevalence and intensity were 53.5% and 3 mf/mg skin snip respectively. There was significant decrease (p<0.05) in the prevalence and intensity of infection in the participating community at post-treatment 1, (Prevalence 11.7%; intensity, 1.2mf/mg skin snip) which amounted to 78% and 60% reduction respectively. The prevalence rate of infection obtained at post-treatment 2 was 9.1% while the intensity rate was 1.1mf/mg skin snip. There was no significant reduction in both the prevalence and intensity of infection between post-treatment 1 and post-treatment 2. There was reduction in microfilarial load in all age groups following the second treatment, which resulted in similar intensity of infection for all age group. Some reactive skin symptoms such as pruritus decreased from 66.1% to 37.4% at post-treatment 1 and later increased to 43.9% at post-treatment 2. Other reactive skin symptoms such as leopard skin, hanging groin, onchocercomata, lymphoedema of the limb and external genitalia remained unchanged. Despite this appreciable impact on microfilarial load and some reactive skin symptoms, ivermectin alone was not able to interrupt transmission of onchocerciasis in this hyper-endemic area due to the problem of re-invasion and the reservoir of infection in the non-compliant group and the excluded members of the community.

Keywords: Onchocerca volvulus, Ivermectin, treatment.

NQJHM Vol. 14 (3&4) 2004: pp. 211-216