The Wisconsin Department of Natural Resources confirmed in a May 13 press release that several fox kits were infected with the currently circulating H5N1 strain of highly pathogenic avian influenza (HPAI).
It is likely that the foxes contracted the virus after eating or coming into contact with infected birds in their natural environment.
This detection in wild red foxes is the first report of mammalian HPAI infections in the United States, although cub infections have since been reported in Minnesota and Michigan. It was also detected in foxes in Ontario, Canada, earlier this month.
The virus was identified at the Wisconsin Veterinary Diagnostic Laboratory at the University of Wisconsin-Madison and confirmed by the National Veterinary Services Laboratories, a diagnostic testing laboratory of the USDA’s Animal Plant and Health Inspection Service.
“Kits appear to develop severe clinical illness and die rapidly after infection, similar to what we see in the spread events of this virus in other non-host species, such as domestic poultry and raptors (birds of prey , including hawks and eagles),” says Betsy Elsmo, diagnostic pathologist at WVDL and associate professor of clinical diagnostics at the UW School of Veterinary Medicine.
After noticing an increase in the number of sick fox kits being brought to the Dane County Humane Society (DCHS) Wildlife Center, staff submitted several deceased animals to the WVDL for further testing.
WVDL staff ruled out common causes of death in foxes and expanded their search for answers.
Previously, cases of HPAI in wild foxes had been detected in the Netherlands. Erin Lemley, a wildlife veterinary technician at the DCHS Wildlife Center, and Shawna Hawkins, a clinical instructor in zoological medicine at the School of Veterinary Medicine, reviewed the information and determined that it matched what they observed in deceased animals.
Positive HPAI kits were brought to the DCHS Wildlife Center from several counties in Wisconsin.
Currently, foxes do not appear to spread HPAI to other species and no infected adult foxes have been reported. There have been no reports of spread to pets such as cats and dogs.
“Current research indicates that similar HPAI virus strains may be able to infect domestic dogs, but there is no evidence that domestic dogs develop disease or play a significant role in the transmission of this virus,” Elsmo adds.
Humans remain at low risk of developing HPAI infection, but you should always refrain from approaching or handling sick or dead wild animals. If you encounter sick or deceased wildlife, please visit the Wisconsin Department of Natural Resources webpage for additional guidelines and information.
The virus that causes avian influenza is common in wild birds, and many species of waterfowl and shorebirds can harbor avian influenza viruses without showing symptoms of illness.
Less commonly, strains such as the currently circulating H5N1 strain can infect and cause disease in wild birds and other animals.