Something is wrong with the foxes. That’s what callers to the Dane County Humane Society in Wisconsin still say in April, when they report foxes, or young foxes, behaving in strange ways: swaying, grabbing. grab or try to get up. The kits, often lethargic and wandering alone, also seem unusually approachable, showing little fear of humans.
“We keep getting calls,” said Erin Lemley, a wildlife veterinary technician at the humane society’s wildlife center. “And the foxes started coming.”
Some of the kits received for treatment have been silenced and withdrawn, she said. Others stagger around or have convulsions, their heads dizzy, their eyes blinking rhythmically. After staff members ruled out rabies, low blood sugar, and other potential causes, lab testing discovered a surprising culprit: a highly virulent strain of bird flu.
It was not a pleasant surprise, said Dr Shawna Hawkins, a zoo and wildlife veterinarian at the University of Wisconsin-Madison.
The virus, a type of bird flu known as Eurasian H5N1, spread rapidly in the United States this spring, infecting poultry flocks in 36 states and causing poultry to be culled. series.
But this version of the virus seems to do more damage to wild birds than previous strains, which found their way into ducks, geese, gulls and terns, among many others. That means the virus poses a great danger to those birds’ predatory mammals, including the wild red fox.
At least seven US states have detected the virus in red fox kits, which appear to be particularly deadly. Two lynx in Wisconsin, a wolf in Michigan and a skunk in Canada have also tested positive for the virus, as have foxes, otters, lynxes, polecats and badgers in Europe. (Two human cases, one in the United States and one in the UK, have also been reported, both in close contacts of birds.)
Fascinating world of birds
Experts say there is no evidence that mammals play an important role in spreading the virus and the risk to humans remains low. Richard Webby, influenza virologist at St. “This is still an avian virus,” said Jude of Memphis.
But evolution is a numbers game, he says, and the more mammals infect with the virus, the better chance it has of spotting new mutations that could help it spread among foxes, lynx or even lynx. even humans.
“What needs to be done to get this virus to move from a duck or chicken virus to a mammalian virus will have a better chance of replicating in those mammalian hosts,” said Dr. Webby. “. “So that’s why when we see mammals infected with this virus, we pay attention.”
The foxes bend
The new strain of the virus spread through Europe, Africa, the Middle East and Asia last year, causing outbreaks in wild and domestic birds. It is also present in a number of wild mammals, including fox kits in the Netherlands in spring 2021.
By the end of that year, the virus had reached North America. As it ran through migratory American bird populations this spring, reports began to emerge of infected fox kits – first in Ontario and then in Wisconsin, Minnesota, Michigan, Iowa, Alaska , Utah and New York.
In some birds, the virus causes obvious neurological symptoms, and many infected foxes also exhibit abnormalities. They convulse, walk in circles, and salivate excessively. In the most severe cases, the foxes have convulsions; Experts say death often follows.
Betsy Elsmo, a pathologist at the Wisconsin Veterinary Diagnostic Laboratory who performed the necropsies, said autopsies revealed multiple kits with pneumonia. When he examined the animals’ brain tissue under a microscope, Dr. Elsmo saw obvious signs of damage.
“There is a lot of inflammation in the brain microscopically,” she said. “The pattern of injury that I see is consistent with a viral lesion.”
The virus appears to be doing more harm to fox kits than adults so far, experts say, likely because the young animals don’t yet have developed immune systems. full, experts said.
But the overall rate of infection and death is unknown. “We are only getting anecdotal reports in the wild right now,” said Michelle Carstensen, wildlife health program supervisor for the Minnesota Department of Natural Resources.
Wisconsin officials also detected the virus in two adult lynx this spring. Dr Lindsey Long, wildlife veterinarian for the Wisconsin Department of Natural Resources, said in an email: “Both lynx showed no fear of humans. “They were recorded sitting on the porch and close to human activity without the usual fear response.”
One lynx appeared to be shivering, while the other appeared to be having trouble breathing, she added. The lynx that were euthanized had microscopic brain lesions that were “quite similar” to those of the affected foxes, Dr. Elsmo said.
Megan Moriarty, a wildlife veterinary specialist at the state’s Department of Natural Resources, said the virus was also recently detected in a prairie wolf in Michigan.
Scientists suspect that the animals are contracting the virus by eating infected birds. In a laboratory study, researchers previously demonstrated that red foxes that are fed infected poultry carcasses can become infected with the virus, and then shed.
While it’s possible the virus has evolved in ways that make it better for infecting mammals, the scientists say the most likely explanation for the sudden increase in species Infected mammals are caused by this lineage infecting large numbers of wild birds, increasing the likelihood that hunters and scavengers may stumble across contaminated food sources. sick.
So far, the virus does not appear to have caused enough illness or death in wild mammal species to put them at risk, experts say. And there is no evidence of long-term mammalian-to-mammal transmission. “Mammals are often considered the death route for highly pathogenic avian influenza,” said Dr. Moriarty.
An initial analysis of viral genomes from Wisconsin fox kits showed that the infections were essentially a series of repeats – the result of foxes coming into contact with infected birds, rather than the birds. It’s not that foxes transmit the virus to each other. Dr Elsmo said: “The preliminary data we have suggests that these are all independent spillover events.
But many things remain unclear, including whether the virus self-forms in wild birds over long periods of time, which could pose a long-term risk to mammals.
And even isolated mammalian infections provide viruses with new opportunities to evolve. Dr Jolianne Rijks, a veterinarian at the Dutch Center for Wildlife Health said: “There is a risk that it adapts and then spreads between mammals, and then you encounter a new problem”.
Some state officials say they have begun testing sick mammals more often for the virus, especially those with neurological symptoms. Animals that test positive also need to have their virus sequenced so that scientists can monitor for any worrisome changes, Dr. Webby said.
Experts also encourage the public to report any wild animals exhibiting strange behavior. “That’s how all of this started,” Dr. Elsmo said, “when residents see the kits behaving abnormally and report them.”
