A Cochrane review [Abstract] 1 included 4 studies; 2 small studies (n=398) in which people with onchocercal infection were given one dose of ivermectin or placebo and followed up for one year; and 2 larger community-based studies (n=4941) whereby all individuals in selected communities were treated every six or 12 months with ivermectin or placebo, whether or not they were infected, and followed for two to three years. Treating people who have onchocerciasis with ivermectin reduced the number of microfilariae in their skin and eye(s) and reduced the number of punctate opacities. There was weaker evidence that ivermectin reduced the risk of chorioretinitis. The studies were too small and of too short a duration to provide evidence for an effect on sclerosing keratitis, iridocyclitis, optic nerve disease or visual loss.
One community-based study in communities mesoendemic for the savannah strain of O.volvulus showed that annual mass treatment with ivermectin reduces the risk of new cases of optic nerve disease and visual field loss (RR 0.60, 95% CI 0.41 to 0.89; 1 study, n=636). The other community-based study of mass biannual treatment of ivermectin in communities affected by the forest strain of O.volvulus demonstrated reductions in microfilarial load, punctate keratitis (RR 0.33, 95% CI 0.22 to 0.49; 1 study, n=551) and iridocyclitis (RR 0.62, 95% CI 0.43 to 0.9; 1 study, n=554) but not sclerosing keratitis, chorioretinitis, optic atrophy or visual impairment (RR 1.08, 95% CI 0.33 to 3.50; 1 study, n=485). The study was underpowered to estimate the effect of ivermectin on visual impairment and other less frequent clinical signs. The studies reported some adverse effects, in particular an increased risk of postural hypotension in people treated with ivermectin.
Comment: The quality of evidence is downgraded by inconsistency (variability in results across studies), and by imprecise results (few events). The review authors have decided to no longer update this review. The basis for this decision is in part due to ivermectin as the current standard of care which prohibits future placebo-controlled trials. Additional advances in the treatment and elimination of onchocerciasis now include combination treatments with a single dose of ivermectin plus daily doxycycline; future Cochrane reviews addressing additional therapies will add to the current evidence summarised here.
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