Geographical and Spatial Analysis of Loa loa Prevalence in Endemic African Countries
Natalie Wright, MPH Candidate, Department of Global Health
Summer 2013 GIS in Public Health
Introduction
Loa loa, also known as the “African Eye Worm,” is an arthropod borne
disease prevalent throughout Africa. It is a filarial parasite that is
often neglected and the habitat and transmission for breeding is
shown to vary by many ecological/ geographical factors (See Image 1).
Negative implications with Onchocerciasis, another filarial parasite in
Image 1: Loa loa filarial worm and Chrysops
vector (deerfly).
conjunction with Loa loa make control and treatment difficult if not
Source: CDC (2010)
impossible. In a study focusing on 11 African countries, the
spatial distribution was studied in conjunction with the prevalence of Loa loa. The goal of this project is
to determine if geographical and environmental factors in certain areas of Africa correlate to Loa loa
prevalence.
Objective
-To determine the spatial distribution of Loa loa prevalence and its relationship with riverine areas.
-To describe potential geographical/environmental attributes associated with high and low
prevalence rates.
Methodology/Data
Data from a RAPLOA (Rapid Assessment Procedure for Loiasis) survey is available for dates
between 2002-2010 in villages in 11 countries and shows geographical prevalence of eye worm
history (Zoure et al, 2011). Geographical models displaying riverine hydrologic networks in 11
countries with known prevalence were created. Areas of high and low prevalence were analyzed
further to describe geographical/environmental attributes.
Map1:
11 Loa loa endemic countries in Africa displaying
prevalence and riverine data.
Map 2:
11 African Countries where RAPLO was performed
and prevalence data obtained.
.
Conclusion
The resulting findings of the survey in the 11 targeted countries suggest a association between Loa
loa presence and riverine areas. We observed two patterns, the northern countries showed low
prevalence rates whereas the southern countries have higher prevalence rates. Further comparative
analysis on the Sahara Desert and ecological implications on Loa loa should be investigated.
Additional status testing is difficult due to medicinal side affects when subjects are treated for
Onchocerciasis in conjunction with Loa loa. Monitoring, implementation, statistical analysis and
strengthening strategies should be addressed to promote safe and proper community directed
treatment.
References
Zoure, H. G. M., Wanji, S., Noma, M., Amazigo, U. V., Diggle,
P. J., Tekle, A. H., et al., (2011). The geographic distribution of loa loa in africa: results of large-scale implementation of the rapid assessment procedure for loiasis (raploa). PLos Neg Trop Dis,
5(6), 1-11. doi: 10.1371/journal.pntd.0001210
Kelly-Hope, L.A., Brockarie, M.J., Molyneux, D.H., (2012).
Loa Loa ecology in central Africa: role of the congo river system. PLoS Negl Trop Dis, 6(6): e1605. doi: 10.1371/journal.pntd.0001605
Map 3:
Geographical Google Earth model of a local riverine area in Gabon.
Gabon is known to be associated with high Loa loa worm prevalence.
Map 4:
Geographical Google Earth model of a local riverine area in Ethiopia.
Ethiopia is known to be associated with low Loa loa worm prevalence.