Environmental Factors Associated With Loa loa Microfilaria Prevalence and Intensity in Diverse Bioecological Zones of Cameroon

Xavier Badia-Rius,Mark J Taylor,Samuel Wanji,Hannah Betts,David Molyneux,Louise A Kelly-Hope

doi:10.3389/fitd.2021.668641

Xavier Badia-Rius, Mark J Taylor + Show 4 more

Open Access

https://doi.org/10.3389/fitd.2021.668641

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Abstract

Loiasis (African Eye Worm) is a filarial infection caused by Loa loa and transmitted by Chrysops vectors, which are confined to the tropical rainforests of Central and West Africa. Loiasis is a major impediment to control and elimination programmes that use the drug ivermectin due to the risk of serious adverse events. There is an urgent need to better refine and map high-risk communities. This study aimed to quantify and predict environmental factors associated with loiasis across five bioecological zones in Cameroon. The L. loa microfilaria (mf) prevalence (%) and intensity (mf number/ml) data from 42 villages within an Equatorial Rainforest and Savannah region were examined in relation to climate, topographic and forest-related data derived from satellite remote sensing sources. Differences between zones and regions were examined using nonparametric tests, and the relationship between L. loa mf prevalence, mf intensity, and the environmental factors using polynomial regression models. Overall, the L. loa mf prevalence was 11.6%, L. loa intensity 927.4 mf/ml, mean annual temperature 23.7°C, annual precipitation 2143.2 mm, elevation 790 m, tree canopy cover 46.7%, and canopy height 19.3m. Significant differences between the Equatorial Rainforest and Savannah region were found. Within the Equatorial Rainforest region, no significant differences were found. However, within the Savannah region, significant differences between the three bioecological zones were found, and the regression models indicated that tree canopy cover and elevation were significant predictors, explaining 85.1% of the L. loa mf prevalence (adjusted R2 = 0.851; p&lt;0.001) and tree cover alone was significant, explaining 58.1% of the mf intensity (adjusted R2 = 0.581; p&lt;0.001). The study highlights that environmental analysis can help delineate risk at different geographical scales, which may be practical for developing larger scale operational plans for mapping and implementing safe effective interventions.

Highlights

Loiasis is a filarial nematode infection caused by the parasite Loa loa and transmitted by tabanid flies of the genus Chrysops [1,2,3]
The Equatorial Rainforest region in South-West Province consisted of the deciduous equatorial rainforest (DERF) and dense-humid equatorial rainforest (DHERF) zones
The L. loa mf prevalence distribution in relation to the land cover type in each bioecological zone is shown in Figures 1A, B

Summary

Introduction

Loiasis is a filarial nematode infection caused by the parasite Loa loa and transmitted by tabanid flies of the genus Chrysops [1,2,3]. There is a need to better refine and map high-risk loiasis communities to enable the deployment of new diagnostics, alternative intervention and heightened care strategies [8, 9]. This is critical as loiasis covers a vast geographical area and many high-risk communities are in remote hard-to-reach areas [2]. There is a need for more innovative cost-effective approaches, and the availability of satellite remote sensing technology provides an opportunity to use large-scale maps and modelled data to examine factors associated with transmission [10]. Environmental factors are important for vectorborne diseases and understanding key drivers may help to define their specific niche [11]

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