Three grizzly bears were euthanized in Montana after they became ill and tested positive for the highly pathogenic avian influenza (HPAI) virus, according to the state's Department of Fish, Wildlife & Parks.
These were the first documented cases of bird flu in a grizzly in Montana and the first nationwide for this outbreak of HPAI, according to Dr. Jennifer Ramsey, the department's wildlife veterinarian.
The juvenile bears were in three separate locations in the western part of the state during the fall, the Department of Fish, Wildlife & Parks said in a statement.
The bears "were observed to be in poor condition and exhibited disorientation and partial blindness, among other neurological issues," the statement said. "They were euthanized due to their sickness and poor condition."
Avian influenza -- commonly called bird flu -- is a naturally occurring virus that spreads quickly in birds. There were documented cases of HPAI in a skunk and a fox in Montana last year, and the virus has been seen in raccoons, black bears and a coyote in other states and countries, according to the Montana agency.
"The virus is spread from one bird to another," Dr. Ramsey told CNN via email. "These mammals likely got infected from consuming carcasses of HPAI infected birds."
"Fortunately, unlike avian cases, generally small numbers of mammal cases have been reported in North America," Ramsey said. "For now, we are continuing to test any bears that demonstrate neurologic symptoms or for which a cause of death is unknown."
While finding three grizzlies with bird flu in a short period of time may raise concerns, Ramsey said it may well be that there have been more cases that haven't been detected.
"When wildlife mortalities occur in such small numbers or individuals, and in species like skunks, foxes and bears that don't spend a lot of time in situations where they are highly visible to the public, they can be hard to detect," the wildlife veterinarian said.
"When you get that first detection you tend to start looking harder, and you're more likely to find new cases," she said. "When a large number of birds are found dead on a body of water, it gets noticed and reported... when someone sees a dead skunk, they may think nothing of it and not report it."
While it's unknown just how prevalent the virus is in wild birds, "we know that the virus is active basically across the entire state due to the wide distribution of cases of HPAI mortality in some species of wild birds," Ramsey said.
The US Centers for Disease Control and Prevention said in November the country was approaching "a record number of birds affected compared to previous bird flu outbreaks," with more than 49 million birds in 46 states dying or being killed due to exposure to infected birds.
Human infections with bird flu are rare but are possible, "usually after close contact with infected birds. The current risk to the general public from bird flu viruses is low," the CDC says on its website.
The Montana Department of Fish, Wildlife & Parks is asking people to report any birds or animals acting "unusual or unexplained cases of sickness and/or death."
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