Bats and wild primates are believed to be the main source of human outbreaks of the deadly Ebola virus, including the one that has ravaged Western Africa with hemorrhagic fever for the past six months and taken more than 2,100 lives.
While scientists have been studying this link for decades, a new analysis of the data of all known transmissions of the virus from animals to humans indicates that the area of potential infection is much larger than was previously thought, encompassing an area that is home to more than 20 million people.
The map, which can help predict where humans are most likely to come into contact with infected animals, was published in the journal eLife on Monday and produced by a team of researchers led by members of the University of Oxford's Department of Zoology. As world health authorities work to get the largest Ebola outbreak in history under control, the new model could help prevent similarly disastrous outbreaks in the future.
The first step in an Ebola outbreak is the "spillover" transmission from animal to human — often linked to the hunting and eating of infected animals, commonly referred to as bushmeat. The spillover incident that is believed to have started the current outbreak occurred in the Democratic Republic of the Congo when a woman butchered an infected bush animal that her husband had brought home.
After the initial spillover occurs, the virus subsequently spreads through a human-to-human transmission chain.
The research team found that infected animals that were previously thought to be contained within a "zoonotic niche" in central Africa are distributed throughout a swath of land that spans 22 countries, from Guinea to Ethiopia, including countries that haven't reported any incidents of Ebola.
According to David Pigott, the study's lead researcher, the team found that there was very little difference between the environmental factors (such as temperature, vegetation, and elevation) that defined previous outbreaks compared to the one that has unfolded in Sierra Leone, Guinea, Liberia, and Nigeria - although strains of the virus may be different.
"The map can be used if people want to understand the entire epidemiology of the disease," Pigott told VICE news. He said that outlining these areas on a map is "a great starting point to establish surveillance systems."
Beyond covering a more expansive region, the study concluded that 22 million people inhabit the updated at-risk transmission area for Ebola. Pigott said that the population of the countries within the revised region has changed dramatically since Ebola was discovered in 1976.
Pigott and his team found that urban and rural populations in all of the at-risk countries have both grown in size and become more interconnected, facilitating the subsequent spread of Ebola outbreaks over the last four decades, while the virus is also interacting with human populations in a different way.
"We have shown that the human population living within this niche is larger, more mobile and better internationally connected than when the pathogen was first observed," the report says. "As a result, when spillover events do occur, the likelihood of continued spread amongst the human population is greater, particularly in areas with poor healthcare infrastructure."
Pigott said that officials could use the map his team created to prepare for future outbreaks and prioritize its focus on particular zones. He explained that understanding what areas are at risk and well connected could help predict a large outbreak.
Implementing better preventative and predictive measures will be essential to the handling of future Ebola outbreaks, which we're likely to see once every year or so for the foreseeable future, according to University of Reading virologist Ben Neuman. He told VICE News that the new map is a welcome tool for health officials to use to preemptively build up response efforts, the development of which will be crucial to the region.
"You almost have to have something ready before the outbreak," he said. "The outbreak in West Africa probably would have been under control by now if that was the case. If there'd been a little bigger push at the beginning stage, that's when it would have done the most good."
By understanding what areas are likely to experience an outbreak, officials could work on strengthening local healthcare systems, building treatment centers, and establishing networks of trained healthcare providers. Neuman said that developing this infrastructure will make all the difference in the next outbreak.
"I don't think we'll ever be at a stage where we can pinpoint where Ebola is going to happen," Pigott said. "But we can predict where to concentrate research and infrastructure that can support or be prepared for any future outbreaks."
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