Bats harbour more deadly viruses than was previously thought, scientists say.
Researchers have found that henipaviruses, which spread to other animals and humans, and a disease that is similar to rabies are widespread in a species of fruit bat found in Africa.
The team says this poses a potential risk to human health, because the bats roost close to cities and are also hunted for food.
The study is published in Nature Communications.
Professor James Wood, an epidemiologist from the University of Cambridge, said: "I think that it's no immediate cause for panic - these viruses have probably been there for a very long time in bats.
"But I think that it does raise questions relating public health surveillance and care that should be taken to avoid possible contact that might result in transmission."
Bats are a well-known mixing pot for viruses, some of which can spread to other animals and humans.
The origins of diseases such as Sars and Ebola can be traced back to these flying mammals, and they have also been implicated in the spread of the new deadly Mers virus.
In Africa, the straw-coloured fruit bat (Eidolon helvum), the continent's most widely distributed bat, is known to host different infectious diseases. But until now the extent has not been known.
To find out more, researchers tested more than 2,000 bats in 12 African countries.
They found that just under half (42%) were harbouring henipaviruses, which can be deadly if they spread to other animals and humans, particularly in the form of the Hendra virus.
Prof Wood explained: "In Australia... the virus has spread into horses, and from horses, this virus has passed into vets tending sick horses, and this has killed a a number of people in Australian.
"In Malaysia there was a huge outbreak associated with pigs in 1999, in which more than 100 pig farmers and slaughter house workers died."
About a third of the fruit bats were also found to be infected with the rabies-like Lagos bat virus.
Prof Wood said there was no evidence yet that the two viruses had spread to humans in Africa.
But he added that in some areas disease surveillance was poor, and there could have been cases that went undetected.
The researchers said improved vigilance was needed.
"For Lagos bat virus I think there are particular risks for those people who hunt bats, because it is most likely transmitted by bites," said Prof Wood.
"But perhaps more worrying for the family of henipaviruses, there may well be some transmission from urine and that raises very large questions for people who live in close proximity to large bat roosts."
The team said that removing the bats or culling them was not an option, and could even spread the viruses further.
They added that the animals were also a crucial part of the ecosystem.
"Making sure the animals live in a protected zone is probably is safer in terms of direct risks than intervening to make the bat colonies move on," explained Professor Wood.
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