Scientists find evidence of a ‘different’ flu virus in bats

By Dr. Ananya Mandal, MDFeb 28 2012

Scientists have found evidence of flu in bats. The risk of transmission to humans is unclear.

They were surprised to find genetic fragments of a flu virus in bats. So far, scientists haven't been able to grow it, and it's not clear if — or how well — it spreads. Flu bugs are common in humans, birds and pigs and have even been seen in dogs, horses, seals and whales, among others. About five years ago, Russian virologists claimed finding flu in bats, but they never offered evidence.

“Most people are fairly convinced we had already discovered flu in all the possible” animals, said Ruben Donis, a Centers for Disease Control and Prevention scientist who co-authored the new study.

The CDC has an international outpost in Guatemala, and that's where researchers collected more than 300 bats in 2009 and 2010. The research was mainly focused on rabies, but the scientists also checked specimens for other germs and stumbled upon the new virus. The virus - designated H17, was in the intestines of little yellow-shouldered bats, said Donis, a veterinarian by training. These bats eat fruit and insects but don't bite people. Yet it's possible they could leave the virus on produce and a human could get infected by taking a bite.

The researchers speculated that some bats caught flu centuries ago and that the virus mutated within the bat population into this new variety. Scientists haven't even been able to grow the new virus in chicken eggs or in human cell culture, as they do with more conventional flu strains. But it still could pose a threat to humans. For example, if it mingled with more common forms of influenza, it could swap genes and mutate into something more dangerous.

The research was posted online Monday in the journal Proceedings of the National Academy of Sciences.

All they found was a segment of genetic material, said Richard Fulton, a bird disease researcher at Michigan State University. What they should do is draw blood from more bats, try to infect other bats and take other steps to establish that the virus is spreading among the animals, he continued. “In my mind, if you can't grow the virus, how do you know that the virus is there?”

Donis said work is going on to try to infect healthy bats, but noted there are other viruses that were discovered by genetic sequencing but are hard to grow in a lab, including hepatitis C.

“We are far away from speculating on any pandemic potential of this virus, but finding this ancient influenza subtype stresses again that bats are an important source of animal viruses," says Ab Osterhaus, head of virology at Erasmus Medical Center in Rotterdam, the Netherlands, who was not involved in the work.

“With more than 1,200 known species, bats are the second-largest mammal group, so it’s not surprising that they carry a large diversity of viruses,” says Jon Epstein, a veterinary epidemiologist at EcoHealth Alliance in New York. “Finding older lineages of influenza in bats doesn’t necessarily increase the risk of influenza emerging into human populations, but it does help us understand the diversity of flu viruses in nature and how genes may be swapped between strains and species.”

Donis acknowledges that surveillance is costly and time-consuming, but argues that we should increase efforts to track both known and emerging pathogens. “The real questions are ‘where else could we find influenza?’ and 'have we looked carefully everywhere?'” he says.