While they provide a vital service in pollinating flowers, keeping insect numbers in check, and spreading seeds around the forests in which they live, bats are also known to harbor some of the most deadly diseases we know about. A new study has managed to map which regions are most at risk from viruses jumping between the flying mammals and humans, with sub-Saharan Africa and South East Asia topping the list. By knowing where transmission is most likely to occur, it could help prevent future outbreaks on the scale seen in West Africa.

Almost two-thirds of what are classed as human-emerging infectious diseases, which are those that have increased in incidence within the past 20 years or are expected to do so in the near future, are known as “zoonotic.” These are diseases that are specifically passed between animals and humans. Bats are known to be reservoirs for many potentially deadly diseases (from rabies to Ebola), meaning they are infected by the viruses and can spread them, but don’t succumb to the disease themselves. Why they are so seemingly good as reservoirs is still little understood, although the impact was dramatically demonstrated by the 2014 Ebola outbreak in West Africa two years ago.

^{Bats are often eaten as bushmeat, such as in New Guinea, Indonesia. South East Asia was found to be a hotspot where diseases might be able to easily jump between bats and humans. Sergey Uruadnikov/Shutterstock}

It was for these reasons that the researchers decided to focus on bats for their study, looking at which areas were most at risk of diseases jumping between the animals and the human population living in the region. They analyzed over 110 years of data on the number of bat species in specific regions, where bats carried the most viruses, and in which areas did people have high contact with the animals, among other factors.

They found that different regions scored highly for different factors, but that when all were taken into account, West Africa came out as the region with the highest risk of zoonotic diseases being passed between bats and people.

^{The data shows which regions have A) the highest number of bat-human shared viruses and B) the highest diversity of viruses found within bats. Brierley et al. 2015}

“We are seeing risk hotspots for emerging diseases where there are large and increasing populations of both humans and their livestock,” explains Liam Brierley, first author of the study published in The American Naturalist, in a statement. “As a result, settlements and industries are expanding into wild areas such as forests and this is increasing contact between people and bats. People in these areas may also hunt bats for bushmeat, unaware of the risks of transmissible diseases which can occur through touching body fluids and raw meat of bats.”

By knowing which areas are more likely to be at the epicenter of an emerging infectious disease outbreak, the researchers hope that surveillance can be increased and that the data can inform local organizations and governments about preventative action. Knowledge like this could help to stop, or at least stem, a situation on the scale we saw in West Africa, where whole communities were devastated by Ebola.