Abstract
Introduction: Although many studies have investigated the probability of Ebola virus disease (EVD) outbreaks while other studies have simulated the size and speed of EVD outbreaks, few have investigated the environmental and population-level predictors of Ebola transmission once an outbreak is underway. Identifying strong predictors of transmission could help guide and target limited public health resources during an EVD outbreak. We examined several environmental and population-level demographic predictors of EVD risk from the West African epidemic. Methods: We obtained district-level estimates from the World Health Organization EVD case data, demographic indicators obtained from the Demographic and Health surveys, and satellite-derived temperature, rainfall, and land cover estimates. A Bayesian hierarchical Poisson model was used to estimate EVD risk and to evaluate the spatial variability explained by the selected predictors. Results: We found that districts had greater risk of EVD with increasing proportion of households not possessing a radio (RR 2.79, 0.90-8.78; RR 4.23, 1.16-15.93), increasing rainfall (RR 2.18; 0.66-7.20; 5.34, 1.20-23.90), and urban land cover (RR 4.87, 1.56-15.40; RR 5.74, 1.68-19.67). Discussion: The finding of radio ownership and reduced EVD transmission risk suggests that the use of radio messaging for control and prevention purposes may have been crucial in reducing the EVD transmission risk in certain districts, although this association requires further study. Future research should examine the etiologic relationships between the identified risk factors and human-to-human transmission of EVD with a focus on factors related to population mobility and healthcare accessibility, which are critical features of epidemic propagation and control.
Highlights
Many studies have investigated the probability of Ebola virus disease (EVD) outbreaks while other studies have simulated the size and speed of EVD outbreaks, few have investigated the environmental and population-level predictors of Ebola transmission once an outbreak is underway
Liberia and Guinea were similar in case burden, with Liberia having the largest portion of households headed by females and households without toilets
The spatial analysis indicates that districts were more at risk of EVD with increasing rainfall (RRRainfall2 2.18; 95% credible interval 0.66-7.20; RRRainfall3 5.34, 1.20-23.90), urban land cover (RRUrban2 4.87, 1.56-15.40; RRUrban3 5.74, 1.68-19.67), households not possessing a radio (RRRadio2 2.79, 0.90-8.78; RRRadio3 4.23, 1.16-15.93), and years of education (RREducation3 1.58, 0.406.25)
Summary
Many studies have investigated the probability of Ebola virus disease (EVD) outbreaks while other studies have simulated the size and speed of EVD outbreaks, few have investigated the environmental and population-level predictors of Ebola transmission once an outbreak is underway. Fruit bats are believed to be a key reservoir of Ebolavirus, which can cause illness and death in non-human primates such as in apes and monkeys.[8] Human outbreaks are typically started when an individual has come into contact with the blood of an infected mammal or bushmeat[6] the West African outbreak is thought to have begun because of fruit bat exposure.[9] Human-to-human transmission is propagated through direct contact with infected individuals and cadavers.[10] Illness in humans appears two to 21 days after infection and the initial symptoms are fever, headache, and myalgia These symptoms are followed by vomiting, diarrhea, rash, impaired liver and kidney functions, and can result in internal and external bleeding.[8] The case fatality rate for the most recent outbreak was estimated at 71% during the first nine months of the epidemic, which is similar to other outbreaks of Zaire ebolavirus species (60%-90%) and higher than outbreaks from Sudan ebolavirus species (40%-60%).[11]
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