Mutant strains of a common human flu virus have been found in dogs for the first time, prompting concerns that such viruses could start to spread easily among pets—and potentially evolve into dangerous new strains that jump back to humans.
Nanjing Agricultural University virologist Shuo Su and his colleagues identified two dogs in southern China with different mutant strains of the influenza C virus, which infects almost all humans—mostly as children—and usually causes mild illness.
The researchers genetically sequenced these strains and found that mutations affected their structure near the part that binds to a host's cells. These changes mean “it might be on the way to replicate better in dogs,” says Freie Universität Berlin biochemist Michael Veit, a co-author on the new work. People sometimes pass flu viruses to a pet dog, where the contagion typically stops. But the newly found strains' particular mutations suggest that they more likely spread from dog to dog, Veit says.
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Although most adults have already been exposed to influenza C, the researchers say we might have little immunity against a new strain that jumps back to humans after mutating in animals. For a letter published in the Journal of Infection, the scientists describe this finding and say it shows that viruses should be tracked more thoroughly in dogs and other pets through regular testing and sequencing. Cornell University animal virologist Colin Parrish, who was not involved in the study, says he would “certainly advocate” for that.
“We have sort of ignored dogs and cats as potential reservoirs or intermediate hosts,” he says. The U.S. has no formal monitoring programs for viruses in pets, but Parrish's research group routinely surveys dogs for new respiratory viruses.
Two flu viruses are known to spread among dogs around the world: one that jumped from horses and one from birds. In southern China, there are also reports of dogs spreading flu strains from pigs, suggesting the region could be an unusual hotspot for viruses in dogs.
It is too early to say whether dog-borne influenza C will become a problem. More studies are needed to confirm the virus is spreading among these animals and, if so, how easily. But the researchers say it and other viruses should be monitored carefully to catch any emerging disease strains. Increasing surveillance “could be done really, really simply,” Parrish says.
A good place to start would be kennels and similar places where viruses can easily spread and evolve, says University of Nottingham virologist Janet Daly, who was also not involved in the new study. “If you are keeping or farming animals at high density,” she says, “that's where you need to look.”
