Feasibility of Onchocerciasis Elimination Using a "Test-and-not-treat" Strategy in Loa loa Co-endemic Areas.

David J Blok,Joseph Kamgno,Hugues C Nana-Djeunga,Wilma A Stolk,Cedric B Chesnais,Amy D Klion,Sake J De Vlas,Daniel A Fletcher,Charles D Mackenzie,Thomas B Nutman,Sebastien D Pion,Michel Boussinesq,Yannick Niamsi-Emalio

doi:10.1093/cid/ciaa1829

Abstract

BackgroundMass drug administration (MDA) with ivermectin is the main strategy for onchocerciasis elimination. Ivermectin is generally safe, but is associated with serious adverse events in individuals with high Loa loa microfilarial densities (MFD). Therefore, ivermectin MDA is not recommended in areas where onchocerciasis is hypo-endemic and L loa is co-endemic. To eliminate onchocerciasis in those areas, a test-and-not-treat (TaNT) strategy has been proposed. We investigated whether onchocerciasis elimination can be achieved using TaNT and the required duration.MethodsWe used the individual-based model ONCHOSIM to predict the impact of TaNT on onchocerciasis microfilarial (mf) prevalence. We simulated precontrol mf prevalence levels from 2% to 40%. The impact of TaNT was simulated under varying levels of participation, systematic nonparticipation, and exclusion from ivermectin resulting from high L loa MFD. For each scenario, we assessed the time to elimination, defined as bringing onchocerciasis mf prevalence below 1.4%.ResultsIn areas with 30% to 40% precontrol mf prevalence, the model predicted that it would take between 14 and 16 years to bring the mf prevalence below 1.4% using conventional MDA, assuming 65% participation. TaNT would increase the time to elimination by up to 1.5 years, depending on the level of systematic nonparticipation and the exclusion rate. At lower exclusion rates (≤2.5%), the delay would be less than 6 months.ConclusionsOur model predicts that onchocerciasis can be eliminated using TaNT in L loa co-endemic areas. The required treatment duration using TaNT would be only slightly longer than in areas with conventional MDA, provided that participation is good.

Highlights

Mass drug administration (MDA) with ivermectin is the main strategy for onchocerciasis elimination
We explored the impact of conventional ivermectin MDA, in which no one was excluded from treatment because of loiasis
Using conventional ivermectin MDA, elimination of onchocerciasis could be achieved after an average of 15 years

Summary

Introduction

Mass drug administration (MDA) with ivermectin is the main strategy for onchocerciasis elimination. Ivermectin is generally safe but associated with serious adverse events in individuals with high Loa loa microfilarial densities (MFD). Ivermectin is generally safe, the drug has been associated with serious adverse events (SAE) in persons with Loa loa,[1] a filarial parasite endemic in forest areas of Central Africa.[2] People with L. loa microfilarial densities (MFD) greater than 30,000 microfilariae per milliliter (mf/mL) of blood are at high risk of developing potentially fatal encephalopathy.[3, 4] Since the 1990s, more than 500 SAE cases with encephalopathy have been reported after treatment with ivermectin, of which 60 led to death.[4, 5]. There is no WHO-endorsed strategy for hypoendemic onchocerciasis areas with loiasis co-endemicity, which hinders onchocerciasis elimination

Methods

Results

Discussion

Conclusion