Elimination of African Onchocerciasis: Modeling the Impact of Increasing the Frequency of Ivermectin Mass Treatment

Abstract

The African Programme for Onchocerciasis Control (APOC) is currently shifting its focus from morbidity control to elimination of infection. To enhance the likelihood of elimination and speed up its achievement, programs may consider to increase the frequency of ivermectin mass treatment from annual to 6-monthly or even higher. In a computer simulation study, we examined the potential impact of increasing the mass treatment frequency for different settings. With the ONCHOSIM model, we simulated 92,610 scenarios pertaining to different assumptions about transmission conditions, history of mass treatment, the future mass treatment strategy, and ivermectin efficacy. Simulation results were used to determine the minimum remaining program duration and number of treatment rounds required to achieve 99% probability of elimination. Doubling the frequency of treatment from yearly to 6-monthly or 3-monthly was predicted to reduce remaining program duration by about 40% or 60%, respectively. These reductions come at a cost of additional treatment rounds, especially in case of 3-monthly mass treatment. Also, aforementioned reductions are highly dependent on maintained coverage, and could be completely nullified if coverage of mass treatment were to fall in the future. In low coverage settings, increasing treatment coverage is almost just as effective as increasing treatment frequency. We conclude that 6-monthly mass treatment may only be worth the effort in situations where annual treatment is expected to take a long time to achieve elimination in spite of good treatment coverage, e.g. because of unfavorable transmission conditions or because mass treatment started recently.

Modelling the elimination of river blindness using long-term epidemiological and programmatic data from Mali and Senegal

“…ONCHOSIM has been used to inform and support OCP (Plaisier et al, 1997, Winnen et al, 2002) and APOC (Coffeng et al, 2014a, Coffeng et al, 2014b) intervention policies and more recently has been used to evaluate the progress of APOC projects targeting elimination (Tekle et al, 2016). Technical details of the ONCHOSIM model can be found in Supplementary information, 1.2 ONCHOSIM, Coffeng et al (2014a) and Basáñez et al (2016). The ONCHOSIM parameter definitions, descriptions and values are given in Supplementary information, Table S2.…”

Comparison of Doxycycline, Minocycline, Doxycycline plus Albendazole and Albendazole Alone in Their Efficacy against Onchocerciasis in a Randomized, Open-Label, Pilot Trial

“…Current approaches to increase the frequency of MDA from annual to biannual treatments are predicted to improve the chances of reaching the 2020/2025 elimination goals at least in some countries. However, its benefits and costs are highly sensitive to systematic noncompliance and it may not always be feasible to implement biannual treatment, particularly in hard-to-reach populations [6, 7, 42]. In addition, given the problem of re-emergence of infections, suboptimal efficacy of IVM [10] and regions that are co-endemic for Loa loa , the development of new drugs or drug regimens is urgently needed to achieve the elimination of onchocerciasis.…”

“…Simulation studies have suggested that administering IVM at shorter intervals of 6 instead of 12 months intervals have a higher likelihood of eliminating the infection, but incur large logistical costs on health infrastructures of the endemic countries [6, 7]. Immigration of infected persons into areas where filariasis is considered eliminated and IVM treatment has ceased may occur with potential re-emergence of the disease.…”

Research for new drugs for elimination of onchocerciasis in Africa

“…The percentage of the eligible population which participates in CDTI (referred to as ’treatment coverage’) and the percentage of the population which never (or very rarely) takes ivermectin (referred to as ’systematic non-compliers’) (Turner et al., 2013, Coffeng et al., 2014a). The percentage of systematic non-compliers can be extensive.…”