Research Article: African Program for Onchocerciasis Control 1995–2010: Impact of Annual Ivermectin Mass Treatment on Off-Target Infectious Diseases

Date Published: September 24, 2015

Publisher: Public Library of Science

Author(s): Stanimira P. Krotneva, Luc E. Coffeng, Mounkaila Noma, Honorat G. M. Zouré, Lalle Bakoné, Uche V. Amazigo, Sake J. de Vlas, Wilma A. Stolk, Peter Steinmann.

Abstract: Since its initiation in 1995, the African Program for Onchocerciasis Control (APOC) has had a substantial impact on the prevalence and burden of onchocerciasis through annual ivermectin mass treatment. Ivermectin is a broad-spectrum anti-parasitic agent that also has an impact on other co-endemic parasitic infections. In this study, we roughly assessed the additional impact of APOC activities on the burden of the most important off-target infections: soil-transmitted helminthiases (STH; ascariasis, trichuriasis, hookworm, and strongyloidiasis), lymphatic filariasis (LF), and scabies. Based on a literature review, we formulated assumptions about the impact of ivermectin treatment on the disease burden of these off-target infections. Using data on the number of ivermectin treatments in APOC regions and the latest estimates of the burden of disease, we then calculated the impact of APOC activities on off-target infections in terms of disability-adjusted life years (DALYs) averted. We conservatively estimated that between 1995 and 2010, annual ivermectin mass treatment has cumulatively averted about 500 thousand DALYs from co-endemic STH infections, LF, and scabies. This impact comprised approximately an additional 5.5% relative to the total burden averted from onchocerciasis (8.9 million DALYs) and indicates that the overall cost-effectiveness of APOC is even higher than previously reported.

Partial Text: The African Program for Onchocerciasis Control (APOC) is an international program aimed at controlling the disease burden of human onchocerciasis (river blindness) in sub-Saharan Africa (SSA), and elimination of infection where possible, using mass drug treatment (MDA) [1,2]. Since its launch in 1995, APOC and partnering beneficiary countries have scaled up their control activities geographically to at least cover all meso- and hyperendemic areas, averting 8.9 million disability-adjusted life years (DALYs) through 2010, and eventually aiming to treat over 90 million people annually in 16 African countries by 2015, protecting a population at risk of onchocerciasis of 118 million [3,4]. The drug used for mass treatment of onchocerciasis, ivermectin, is distributed and administered in a single dose of 150–200 μg/kg of body weight annually. Chronically ill people, pregnant (or lactating) women, and children under five are excluded from treatment with ivermectin [1].

We assumed that each year, mass treatment would avert some fraction βx of the potential disease burden in treated communities. Based on literature, this fraction was assumed to be 0.5 for ascariasis, trichuriasis, strongyloidiasis and EPSDs, 0.2 for hookworm infections, and 0.1 for LF (Box 1).

The impact of APOC on off-target NTDs has previously been discussed and considered to be important, but difficult to quantify. We estimated that if APOC would not have been there, STH infections, strongyloidiasis, and scabies would have caused a cumulative burden of 1.7 million DALYs lost between 1995 and 2010 in individuals who would otherwise have been treated with ivermectin. We roughly estimated that of these 1.7 million DALYs, mass treatment with ivermectin has averted 500 thousand DALYs. This means that apart from the impact of APOC on the burden of onchocerciasis (8.9 million DALYs averted), there has been an additional 5.5% health impact through the effect of ivermectin mass treatment on off-target NTDs. This indicates that the cost-effectiveness of APOC is even somewhat higher than previously estimated.



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