Why germ-ridden bats don't get sick: Flying mammals that carry disease have a 'super immunity' that protects from the viruses

  • Bats are known to be the source of 100 viruses including Ebola and MERS 
  • Researchers tested the genes and immune systems of black flying foxes
  • The animals had a heightened immune response that was always on
  • Most mammals only mount a immune response when they are infected

They are often incorrectly described as flying rodents, but the reputation of bats alongside pets like mice and rats may in part be due to their ability to spread disease.

Now researchers have discovered for the first time how bats are able to carry some of the most deadly diseases on the planet yet remain unaffected by them.

They found, unlike humans, bats have an overactive immune systems which are switched on all the time rather than just in response to an infection.

Bats (stock picture) are the natural hosts for more than 100 different viruses including the deadly Ebola virus, SARS and MERS. Researchers have discovered the animals avoid getting sick themselves as they have an unusual immune system that is permanently switched on rather than merely responding to infections

Bats (stock picture) are the natural hosts for more than 100 different viruses including the deadly Ebola virus, SARS and MERS. Researchers have discovered the animals avoid getting sick themselves as they have an unusual immune system that is permanently switched on rather than merely responding to infections

Bats are the natural hosts for more than 100 viruses, many of which are lethal in humans.

They were recently discovered to be the source of the deadly Ebola virus while they have also been linked to other illnesses like Middle Eastern Respiratory Syndrome and the Hendra virus.

But exactly how the animals manage to carry these diseases without apparently becoming ill themselves has baffled scientists.

HOW EBOLA BEGAN IN BATS 

The deadly Ebola virus was first discovered in 1976 when it began causing outbreaks in remote African villages.

It was originally thought to have come from gorillas because the outbreaks began shortly after people had eaten meat from the apes.

Other bush meat was also implicated as hunters who suffered cuts were also found to contract the disease.

However, recent research has revealed that bats are the natural reservoir for the virus, and that apes and humans catch it from eating food that bats have drooled or defecated on.

It may also be spread to people by touching surfaces covered in infected bat droppings before then touching a person's eyes or mouths.

The current outbreak seems to have started in a village near Guéckédou, Guinea, where bat hunting is common, according to Doctors Without Borders.

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In the new study, researchers discovered the creatures actually have lower numbers of a group of signalling proteins called interferons, which play a key role in the immune system, than humans.

Yet bats also continually express one of these interferons, giving them a heightened innate immune response even when they are not infected.

It is this that is thought to suppress viruses when they are infected, keeping the animals from getting ill.

In other mammals, having such a constant immune response would cause damage to tissue and lead to severe autoimmune diseases like arthritis.

Dr Michelle Baker, a bat immunologist at the Commonwealth Scientific and Industrial Research Organisation in Australia, said: 'Unlike people and mice, who activate their immune systems only in response to infection, the bats interferon-alpha is constantly 'switched on' acting as a 24/7 front line defence against diseases.

'In other mammalian species, having the immune response constantly switched on is dangerous - for example it's toxic to tissue and cells - whereas the bat immune system operates in harmony.'

A small species of bat known as the Angolan free-tailed bat was recently traced as the source of the recent Ebola epidemic in West Africa.

It is thought that bats roosting in a tree near a village in Guinea, called Meliandou, may have passed the strain of the virus responsible to children playing nearby.

The Ebola virus (pictured) is deadly to humans, but bats are able to carry it without getting ill. The new study suggests their unusual immune systems represses the virus and prevents it from doing harm

The Ebola virus (pictured) is deadly to humans, but bats are able to carry it without getting ill. The new study suggests their unusual immune systems represses the virus and prevents it from doing harm

The Australian black flying fox (pictured) is thought to be one of the bats responsible for spreading the Hendra virus. Researchers studied its genes and immune system as part of their research

The Australian black flying fox (pictured) is thought to be one of the bats responsible for spreading the Hendra virus. Researchers studied its genes and immune system as part of their research

Large reservoirs of a virus responsible for the Severe Acute Respiratory Syndrome, which caused 774 deaths around the world in 2012-2013, was found in Chinese horseshoe bats.

MERS and the Hendra virus, which is lethal to horses but can also be deadly to humans, were also traced to bats.

Dr Baker and her team, whose findings are published in the journal Proceedings of the National Academy of Sciences, examined the genes and immune systems of the Australian black flying fox, a bat that has been linked to the Hendra virus.

She said their findings could now lead to new ways to protect humans from diseases.

'Whenever our body encounters a foreign organism, like bacteria or a virus, a complicated set of immune responses are set in motion, one of which is the defense mechanism known as innate immunity,' said Dr Baker.

Angolan free-tailed bat (young pictured) have been identified as the source of the recent Ebola outbreak in Western Africa

Angolan free-tailed bat (young pictured) have been identified as the source of the recent Ebola outbreak in Western Africa

'We focused on the innate immunity of bats, in particular the role of interferons - which are integral for innate immune responses in mammals - to understand what's special about how bats respond to invading viruses.

'Interestingly we have shown that bats only have three interferons which is only a fraction - about a quarter - of the number of interferons we find in people.

'This is surprising given bats have this unique ability to control viral infections that are lethal in people and yet they can do this with a lower number of interferons.

'If we can redirect other species' immune responses to behave in a similar manner to that of bats, then the high death rate associated with diseases, such as Ebola, could be a thing of the past.'