Environmental factors associated with the distribution of Loa loa vectors Chrysops spp. in Central and West Africa: seeing the forest for the trees

Badia, Xavier, Betts, Hannah, Molyneux, David ORCID: https://orcid.org/0000-0001-8537-7947 and Kelly-Hope, Louise ORCID: https://orcid.org/0000-0002-3330-7629 (2019) 'Environmental factors associated with the distribution of Loa loa vectors Chrysops spp. in Central and West Africa: seeing the forest for the trees'. Parasites & Vectors, Vol 12, Issue 1, e72.

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Abstract

Background
Loiasis is caused by the filarial parasite Loa loa, which is widespread through Central and West Africa and largely confined the tropical equatorial rainforests. The tabanid flies Chrysops silacea and Chrysops dimidiata are the main vectors driving transmission. This study aimed to better define the spatial distribution and ecological niche of the two vectors to help define spatial-temporal risk and target appropriate, timely intervention strategies for filariasis control and elimination programmes.
Methods
Chrysops spp. distributions were determined by collating information from the published literature into a database, detailing the year, country, locality, latitude/longitude and species collected. Environmental factors including climate, elevation and tree canopy characteristics were summarised for each vector from data obtained from satellite modelled data or imagery, which were also used to identify areas with overt landcover changes. The presence of each Chrysops vector was predicted using a maximum entropy species distribution modelling (MaxEnt) method.
Results
A total of 313 location-specific data points from 59 published articles were identified across seven loiasis endemic countries. Of these, 186 sites were included in the climate and elevation analysis, and due to overt landcover changes, 83 sites included in tree canopy analysis and MaxEnt model. Overall, C. silacea and C. dimidiata were found to have similar ranges; annual mean temperature (24.6 °C and 24.1 °C, respectively), annual precipitation (1848.6 mm and 1868.8 mm), elevation (368.8 m and 400.6 m), tree canopy cover (61.4% and 66.9%) and tree canopy height (22.4 m and 25.1 m). MaxEnt models found tree canopy coverage was a significant environmental variable for both vectors.
Conclusions
The Chrysops spp. database and large-scale environmental analysis provides insights into the spatial and ecological parameters of the L. loa vectors driving transmission. These may be used to further delineate loiasis risk, which will be important for implementing filariasis control and elimination programmes in the equatorial rainforest region of Central and West Africa.

Item Type:	Article
Subjects:	QX Parasitology > Helminths. Annelida > QX 301 Filarioidea QX Parasitology > QX 4 General works QX Parasitology > Insects. Other Parasites > QX 505 Diptera WA Public Health > Preventive Medicine > WA 110 Prevention and control of communicable diseases. Transmission of infectious diseases WA Public Health > WA 30 Socioeconomic factors in public health (General)
Faculty: Department:	Biological Sciences > Department of Tropical Disease Biology
Digital Object Identifer (DOI):	https://doi.org/10.1186/s13071-019-3327-9
Depositing User:	Stacy Murtagh
Date Deposited:	07 Feb 2019 12:49
Last Modified:	06 Sep 2019 10:55
URI:	https://archive.lstmed.ac.uk/id/eprint/10131

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