There was something wrong with the fox. It was what a caller to the Dane County Humane Society in Wisconsin continued to say in April, reporting that a fox kit or a young fox behaved strangely. The kits were often lethargic and wandering in their own right, but they seemed very accessible and had little fear of humans.
“We just kept receiving calls,” said Erin Remley, a wildlife veterinary technician at the Wildlife Center in Humanitarian Society. “And the foxes started to come in.”
She said some of the kits hospitalized for treatment were quiet and withdrawn. Others stumbled, had seizures, tickled their heads, and rhythmically flicked their eyes. After staff ruled out rabies, hypoglycemia, and other potential causes, laboratory tests revealed a surprising cause. It is a highly toxic strain of bird flu.
“It wasn’t a fun 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 Eurasia H5N1, spread rapidly in the United States this spring, infecting poultry herds in 36 states and promoting the mass murder of poultry.
However, this version of the virus seems to invade ducks, geese, seagulls, terns, etc., causing far more damage to wild birds than previous strains. This means that the virus poses a high risk to mammals that prey on these birds, such as the wild red fox.
At least seven US states have detected the virus in the red fox kit, but the pathogen appeared to be particularly deadly. Two bobcats in Wisconsin, a coyote puppy in Michigan, and a Mephitidae in Canada also tested positive for viruses, as did European foxes, otters, lynxes, kenagaitachi, and lizards. (Two human cases, the United States and the United Kingdom, have also been reported, both of which were in close contact with birds.)
Fascinating bird world
According to experts, there is no evidence that mammals play an important role in the spread of the virus, and the risk to humans remains low. Richard Webby, an influenza virusologist at St. Jude Children’s Research Hospital in Memphis, said:
But evolution is a number game, and the more mammals infected with the virus, the more opportunities he has to discover new mutations that can help spread to foxes, bobcats, and even humans. Stated.
“What this virus needs to do to transfer from a duck or chicken virus to a mammalian virus is that it is likely to replicate in these mammalian hosts,” Dr. Webby said. “That’s why we pay attention when we see these mammals infected with this virus.”
A new strain of the virus spread to Europe, Africa, the Middle East and Asia last year, causing outbreaks of wild birds and poultry. It also appeared in a small number of wild mammals in the Netherlands in the spring of 2021, including the fox kit fox.
By the end of the year, the virus had invaded North America. Competing for migrating American bird populations this spring, infected fox kits were first in Ontario, followed by Wisconsin, Minnesota, Michigan, Iowa, Alaska, Utah, and New York. Began to be reported in.
In some bird species, the virus caused overt neurological symptoms, and many infected foxes also showed abnormal behavior. They cramped, walked in a circle, and shed excessive saliva. In the most serious cases, the fox developed a seizure. According to experts, death often followed immediately.
Postmortem examinations revealed that many of the kits had pneumonia, said Dr. Betsy Elsmo, a diagnostic pathologist at the Wisconsin Veterinary Diagnostic Institute, who performed the autopsy. When she examined the animal’s brain tissue under a microscope, Dr. Elsmo saw obvious signs of damage.
“Microscopically there was a lot of inflammation in the brain,” she said. “The pattern of injury I saw was consistent with viral lesions.”
So far, experts say the virus is doing more damage to fox kits than to adult foxes. This is probably because young animals have not yet fully developed their immune system.
However, the overall infection and mortality rates are unknown. Michelle Karstensen, director of the Minnesota Natural Resources Department’s Wildlife Health Program, said:
Wisconsin officials also detected the virus in two adult bobcats this spring. “Both bobcats have shown no fear of humans,” Dr. Lindsey Long, a wildlife veterinarian at the Wisconsin Department of Natural Resources, said in an email. “They sat on the porch and noticed that they were close to human activity without the usual horror reactions.”
She added that one bobcat seemed to be shivering and the other seemed to have breathing problems. The euthanized bobcat had a microscopic brain lesion that was “almost identical” to that of the affected fox, Dr. Elsmo said.
The virus was also recently detected in coyote puppies in Michigan, said Dr. Megan Morialty, a wildlife veterinary expert at the State’s Department of Natural Resources.
Scientists suspect that animals are acquiring the virus by eating infected birds. In laboratory studies, researchers have previously shown that red foxes fed dead birds can become infected with the virus and then be shed.
Although the virus may have evolved to improve transmission to mammals, scientists have said that the most likely explanation for the sudden increase in infected mammals is that this strain infects a huge number of wild birds. Scavengers can come across infected food sources, saying that they are increasing the chances of a hunter.
So far, the virus does not appear to cause wild mammals to endanger these species of illness or death, according to experts. And there is no evidence of sustained transmission from mammal to mammal. “Mammals are generally considered a dead end for highly pathogenic avian influenza,” said Dr. Moriarty.
Early analysis of the viral genome from the Wisconsin fox kit suggests that the infection is essentially a one-off series. This is the result of individual foxes coming into contact with infected birds, rather than the foxes infecting each other with the virus. “Preliminary data we have suggests that these are all independent spillover events,” said Dr. Elsmo.
However, much remains unclear, such as whether the virus colonizes wild birds over the long term, and can pose a lasting risk to mammals.
And even isolated mammalian infectious diseases offer new opportunities to evolve into viruses. Dr. Jorian Likes, a veterinarian at the Dutch Wildlife Health Center, said:
Some state officials said virus testing of sick mammals, especially those with neurological symptoms, began more regularly. Animals with positive tests also need to be sequenced with virus samples so that scientists can monitor potential changes of concern, Dr. Webby said.
Experts also encourage the general public to report wildlife that appears to behave strangely. “This was the beginning of everything, because the public is seeing and reporting the anomalous behavior of the kit,” said Dr. Elsmo.