Tracking Fruit Bats May Identify Regions at Greatest Risk for Ebola Epidemic

Researchers are trying to halt future outbreaks of the Ebola virus in Africa by monitoring patterns in which the disease may spread from animals to humans.

In a study published in eLife on September 7, 2014, Oxford University researchers identified hunting and handling of “bush meat” as the most likely source of the current Ebola outbreak in West Africa, as well as previous outbreaks.

The investigators suspected that fruit bats carry the Ebola virus without showing symptoms and then infect other bats and animals in the course of their migration patterns. As a result, preparing and cooking raw meat from this animal reservoir increases the likelihood of primary Ebola transmission.

Compared to previous Ebola outbreaks, the secondary spread of the virus from human-to-human transmission has increased due to demographic changes in the region, the study found.

“Changes in land use and penetration into previously remote areas of rainforest bring humans into contact with potential new reservoirs, while changes in human mobility and connectivity will likely have profound impacts on the dispersion of Ebola cases during outbreaks,” the study authors wrote. “These conditions are thought to have a major role in setting the stage for the current outbreak.”

The current epidemic in West Africa has caused 4269 confirmed and suspected Ebola cases and 2288 related deaths as of September 6, 2014, according to the World Health Organization (WHO). The WHO has warned that the hardest-hit regions are expected to see a surge of thousands of new cases over the next 3 weeks through an intense transmission of the virus.

A large increase in population size coupled with increased urbanization in Africa has caused a paradigm shift in the spread of Ebola. A dense forest with high environmental sustainability spanning 22 countries provides researchers with a predictable environmental niche for zoonotic transmission of the disease.

Based on geography, the countries at the highest risk for animal-to-human Ebola transmission are Nigeria, Cameroon, Central African Republic, Ghana, Liberia, Sierra Leone, Angola, Tanzania, Togo, Ethiopia, Mozambique, Burundi, Equatorial Guinea, Madagascar, and Malawi.

An estimated 22.2 million individuals live in areas suitable for the zoonotic transmission of Ebola, and approximately 97% of them reside in rural areas. Given that the overall African population is more mobile and better connected than in previous Ebola outbreaks, the likelihood of an epidemic has increased, especially in areas with insufficient health care infrastructure.

“The aetiology of Ebola virus disease infection and disease progression means that an international outbreak propagated by air travel remains unlikely, particularly in high-income countries better able to handle (such) cases,” the study authors wrote. “Nevertheless, a non-negligible threat remains, particularly in the low- and middle-income destinations, and the rapid increase in global connectivity of these at-risk regions indicates that international airports could see more imported cases.”

A separate analysis conducted by researcher Lars Skog, of the KTH Royal Institute of Technology, found that health care workers might be able to predict and halt the spread of Ebola outbreaks through geographical models.

“The local population is getting part of their nourishment from bush hunting, leading to contact with the virus that is transmitted via body fluids,” Skog said in a press release. “A guess of mine is that the number of infected fruit bats is a determining factor for an Ebola outbreak. Are there any known factors that may have changed the ecosystem in favor of the bats? Are the bats affected by the virus, too? Do fruit bats always carry the Ebola virus, or is the virus fatal to them, as well? If so, the percentage of infected bats will vary over the years, also depending on the immunology of the species.”