Geostatistical modelling enables efficient safety assessment for mass drug administration with ivermectin in Loa loa endemic areas through a combined antibody and LoaScope testing strategy for elimination of onchocerciasis.

Olatunji Johnson,Lee Hundley,Claudio Fronterrè,Benjamin Amoah,Kisito Ogoussan,Marco Biamonte,Peter J Diggle,Katherine Gass,Sylvie Ntsame Ella,Emanuele Giorgi,Julienne Atsame,Xiao-Nong Zhou

doi:10.1371/journal.pntd.0010189

Abstract

The elimination of onchocerciasis through community-based Mass Drug Administration (MDA) of ivermectin (Mectizan) is hampered by co-endemicity of Loa loa, as individuals who are highly co-infected with Loa loa parasites can suffer serious and occasionally fatal neurological reactions from the drug. The test-and-not-treat strategy of testing all individuals participating in MDA has some operational constraints including the cost and limited availability of LoaScope diagnostic tools. As a result, a Loa loa Antibody (Ab) Rapid Test was developed to offer a complementary way of determining the prevalence of loiasis. We develop a joint geostatistical modelling framework for the analysis of Ab and Loascope data to delineate whether an area is safe for MDA. Our results support the use of a two-stage strategy, in which Ab testing is used to identify areas that, with acceptably high probability, are safe or unsafe for MDA, followed by Loascope testing in areas whose safety status is uncertain. This work therefore contributes to the global effort towards the elimination of onchocerciasis as a public health problem by potentially reducing the time and cost required to establish whether an area is safe for MDA.

Highlights

Loiasis is a major public health issue because of its geographic overlap with onchocerciasis and lymphatic filariasis [1]
Considering the serious adverse events that occur in individuals with high intensity of Loa loa parasite when being treated with ivermectin during the Mass Drug Administration (MDA) program for the elimination of onchocerciasis, there is need for a comprehensive, safe and cost-effective strategy
We propose a hybrid strategy that uses information from the Loa antibody rapid test and the LoaScope diagnostic test to delineate whether an area is safe for MDA

Summary

Introduction

Loiasis is a major public health issue because of its geographic overlap with onchocerciasis and lymphatic filariasis [1]. The elimination of onchocerciasis through community-based Mass Drug Administration (MDA) of ivermectin (Mectizan) is hampered by co-endemicity of Loa loa, as individuals who are highly co-infected with Loa loa parasites can suffer serious and occasionally fatal neurological reactions from the drug. Severe adverse events (SAEs) are largely confined to individuals whose Loa loa microfilaremia load exceeds 30,000 mf/mL as estimated using thick film blood microscopy [2]. The benefits of ivermectin treatment in reducing onchocerciasis-related blindness were deemed to out-weigh the risk of severe adverse events (SAEs) only in areas where onchocerciasis is hyper- or mesoendemic [1]. Where Loa loa is co-endemic, the treatment strategy for onchocerciasis has been confined to areas of high prevalence, leaving a gap in the guidance for how to proceed where onchocerciasis is hypo-endemic

Results

Discussion

Conclusion