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New Clue Found: Why Bats Spread Viruses but Don't Get Sick

Image: A Grey-Headed Flying Fox flies through the air
Scientists say the ability to fly may be one reason bats can harbor dangerous pathogens like Ebola and Nipah viruses without falling ill. Ian Waldie / Getty Images file

If you remember the scary start to the 2011 movie “Contagion,” you’ll recall that a bat is to blame for the outbreak of a deadly airborne virus that mows down Gywenth Paltrow and a cast of dozens.

Not only is such a scenario plausible in real life, scientists now say they may understand better why bats are so good at spreading dangerous pathogens such as Ebola and Nipah virus — the model for the movie — all without getting sick themselves.

Bats’ ability to fly may generate enough energy to cause fevers that fight off infections, including more than 60 viruses that threaten humans, according to researchers with the U.S. Geological Survey, the Zoological Society of London and other top-tier zoology teams.

During flight, bats rev up their metabolic rate 15 times to 16 times higher than non-flying bats. That raises their body temperature to between 100 degrees and nearly 106 degrees Fahrenheit, the equivalent of a pretty high fever in humans.

The fever, in turn, may trigger immune responses that protect the bat from the viruses it carries, according the hypothesis in a new paper led by research zoologist Thomas O’Shea of the USGS and published Wednesday in the journal Emerging Infectious Diseases.

“We know about fever,” said researcher Angela Luis, a disease ecologist now doing postdoctoral work at Princeton University. “Fever is a typical response we experience for infection. Typically, the heat of the fever helps slow pathogen replication and can increase the efficiency of the immune system.”

Conversely, reduced immune system activity during torpor, or rest, may make bats vulnerable to white nose syndrome, a fungal infection that has killed millions of the critters during hibernation in recent years.

The new paper is the first time the hypothesis regarding "flight-as-fever" has been discussed in such depth. Scientists now would like to test their theory.

One way to do that may be to test captive bats trained to fly in wind tunnels to see whether they show heightened immune responses when they’re flying. Scientists also want to test bat viruses in a lab and construct theoretical models for the virus-fighting properties of bats in flight.