TORONTO - Chalk up another species for the wily flu virus. Humans, horses, dogs, whales, seals, birds, cats, ferrets and even raccoons are known to be susceptible to the tiny eight-gene viruses. Researchers in Tennessee have now added giant anteaters to that list.
"Who would have thunk it?" senior author Dr. Melissa Kennedy says with a laugh. "We were pretty amazed."
The February 2007 outbreak, involving 11 adult giant anteaters at Tennessee's Nashville zoo, is reported in an article that will be published in the July issue of the journal Emerging Infectious Diseases. All the anteaters survived the illness.
Beyond the initial "Even anteaters?" reaction, some who study influenza profess to be less taken aback than Kennedy and her co-authors. The virus is so unpredictable, scientists who work in the field expect the unexpected.
"Mainly it's an indication of how much we don't know, and the promiscuity of flu in terms of being able to change hosts and infect and adapt to new situations," says Dr. Jeffrey Hall, who last November added raccoons to the lengthening list of flu's hosts.
The description of the illness in the article creates a vivid mental picture. The extraordinary looking animals suffered "severe" nasal discharge, congestion, loss of appetite and lethargy.
Knowing those nasal discharges could provide hints as to what was afflicting the animals, veterinary staff at the zoo took diagnostic samples and sent them off to the University of Tennessee's college of veterinary medicine in Knoxville.
"Now that's a nasal swab, yes indeed," says Kennedy, who is the clinical virologist at the college.
The zoo's staff didn't know what the animals were suffering from. So Kennedy's team applied bits of the nasal secretions to a variety of different cell cultures, hoping something would grow.
"We had no idea what an anteater is most closely related to, and what cell lines to use. So we threw it on absolutely everything," she explains.
To their surprise, two of three samples produced influenza A viruses of the H1N1 subtype - the human type, not the new swine flu virus.
Sequencing of the genetic blueprints of four of the eight genes of the viruses showed they were virtually identical to the human H1N1 viruses circulating in Tennessee at the time.
Kennedy says there were some small mutations - a few amino acid changes - but it's unclear if they contributed to the virus's ability to jump to a new species. Testing of blood samples taken later from two of the animals confirmed they had antibodies to the virus.
Because it had been an unusually cold winter, the animals had been housed indoors when the outbreak happened. They had no contact with other animals, and limited contact with people.
Though the theory hasn't been proven, the investigation into the source of the sickness points to their main caregiver, who was working at the time with an undiagnosed respiratory illness.
It's not clear whether all the animals caught the flu from the zoo worker, or if some of the spread was anteater to anteater.
"There are many confounding variables to define how this particular virus spread so I can not state beyond speculation how that happened or may have happened at this point," Dr. Sally Nofs, the veterinary services director for the zoo and the first author of the study, says via email.
On the surface of it, it seems unlikely the anteater findings would have any implications for human health. Few of us consort with giant anteaters, which are either endangered or extinct in some regions of the world.
But Hall and others wonder whether, given these findings, there may be undiscovered pools of influenza viruses that circulate among mammals that haven't been identified as natural hosts for flu viruses. If that's the case, might an interplay of viruses among animals species - anteaters to feral pigs, for instance - contribute to the rise of new genetic variations that eventually work their way into humans?
"Clearly they get human influenza so right now we would say that the risk is to the anteaters," says Hall, a research virologist with the U.S. Geological Survey's National Wildlife Health Center in Madison, Wisc., who admits he's no expert on the natural ecology of anteaters.
"But is there an anteater flu out there that we don't know about?"
An avian influenza expert at the University of Minnesota says science assumes viruses from birds and pigs are the major players in the evolution of new flu viruses that make their way into humankind. But Dr. David Halvorson says maybe that's because that's what has been studied.
"So who's to say that maybe we don't have more work to do?" Halvorson says.
"We don't really know how many species of animals are susceptible to these flu viruses. We've only just looked in a few."
