Wild Reservoir of Ebola Larger Than Previously Thought

Scientists have mapped the range of the Ebola virus in the wild. The range is greater than previously estimated with nearly 22 million individuals at risk for exposure to infected animals.

The Oxford-led research team mined the scientific literature for every reported case of Ebola virus since the disease was discovered in 1976. Using spatial and statistical models the scientists mapped each Ebola outbreak and correlated with the ranges of host animal species.

The study, published in eLIFE, predicts the area at risk of Ebola transmission covers most the of Central and West African rain forests. The region intersects with at least 22 countries and covers nearly all of the Democratic Republic of the Congo.

The at-risk region is also the range of several species of African fruit bat. Not coincidentally, Ebola has been detected in previous studies within three fruit bat species that inhabit the Central and West African rainforest, although there may be more. This includes the largest bat species in Africa, the Hammer Head bat. In terms of case burden, bats contributed the largest portion of the identified animal cases while gorillas and chimpanzees made up the rest.

Previous studies have indicated that Ebola-bearing bats do not have symptoms and appear healthy. Gorillas and chimpanzees are susceptible to and die from infection. Frequent outbreaks among the great apes are actually a major environmental concern. Over 5000 gorillas were lost to Ebola between 2002 and 2004.

While it may be troubling that the at-risk population is larger than previously thought the authors of this study call for a rational, calm approach.

“Our map shows the likely ‘reservoir’ of Ebola virus in animal populations. And this is larger than has been previously appreciated. This does not mean that transmission to humans is inevitable in these areas; only that all the environmental and epidemiological conditions suitable for an outbreak occur there,” said author Nick Golding, of Oxford University’s Department of Zoology in interview with the Oxford University Press.

Outbreaks arise from contact between humans and infected animals, usually fruit bats caught for the bushmeat trade. Hunting for bushmeat is a way for rural and impoverished people to sustain basic protein needs when other means are not available or too expensive. In Central and West Africa, fruitbats are hunted for food, smoked, and sold in commercial markets in a widespread distribution chain. One study found that, In Ghana, approximately 1 million bats are hunted annually in just one of the country’s ten administrative regions. Other studies have found that bushmeat consumption decreases as per-capita wealth increases.

Daniel Bausch, an associate professor of tropical medicine at Tulane University School of Public Health and Tropical Medicine said in interview with the Washington Post, “We don’t want to exterminate bushmeat, we just want to keep people from eating it.”

While avoiding a type of meat might be trivial to citizens of more affluent nations, it’s not practical for West and Central Africans, many of whom do not have access to other protein sources. Fish, another traditional source of protein for West Africans, has been on the decline for years. Predatory fishing deals between EU members and weaker West African governments have depleted vital fish stocks in the region, forcing people to hunt for bushmeat. It’s a cycle of hunger, wildlife depletion, foreign exploitation and increased Ebola risk.

Mapping the range of Ebola is a crucial first step toward containing the deadly disease. Governments, public health officials, doctors and laypeople now have a vital tool to understand the virus, predict outbreaks and take precautions. Approaching other emerging infections with the same methodology could help track and contain new outbreaks. However, without effective management and policy, maps like this will be neglected tools at best and forecasts of future tragedies at worst.

Edit: This article erroneously inflated the number of people at risk from 22 million to 220 million. The error has been corrected.