New York: Something was wrong with the foxes. That was what callers to the Dane County Humane Society in Wisconsin kept saying in April, as they reported fox kits, or young foxes, behaving in strange ways: shaking, seizing or struggling to stand. The kits, which were often lethargic and wandering by themselves, also seemed unusually easy to approach, showing little fear of humans.
“We just kept getting calls,” said Erin Lemley, a wildlife veterinary technician at the humane society’s wildlife centre. “And the foxes started coming in.”
Some of the kits that were admitted for treatment were quiet and withdrawn, she said. Others stumbled around or had seizures, their heads ticcing, their eyes flicking rhythmically. After the staff ruled out rabies, low blood sugar and other potential causes, laboratory testing revealed a surprising culprit: a highly virulent strain of bird flu.
The virus, a type of bird flu known as Eurasian H5N1, has been spreading rapidly in the United States this spring, infecting flocks of farmed poultry in 36 states and prompting mass culls of domestic birds.
But this version of the virus appears to be taking a much greater toll on wild birds than previous lineages have, finding its way into ducks, geese, gulls and terns, among many others. That, in turn, means that the virus poses an elevated danger to mammals that prey on those birds, including wild red foxes.
At least seven US states have detected the virus in red fox kits, to which the pathogen appeared to be particularly lethal. Two bobcats in Wisconsin, a coyote pup in Michigan and skunks in Canada have also tested positive for the virus, as have foxes, otters, a lynx, a polecat and a badger in Europe. (Two human cases, one in the United States and one in Britain, have been reported as well, both of which were in people who had close contact with birds.)
There is no evidence that mammals play a significant role in spreading the virus, and the risk to humans remains low, experts said. “This is very much still an avian virus,” said Richard Webby, an influenza virus expert at St Jude Children’s Research Hospital in Memphis, Tennessee.
But evolution is a numbers game, he said, and the more mammals the virus infects, the more opportunities it has to pick up new mutations that could help it spread among foxes, bobcats or even humans.
This article originally appeared in The New York Times.