DENVER – The outbreak of avian influenza that has claimed the lives of thousands of wild birds in Colorado since the spring of 2022 continues to spill over into other susceptible hosts, adding to a growing list of mammalian species affected by the highly pathogenic disease, Colorado Parks and Wildlife officials said Thursday.
A black bear in Huerfano County was euthanized after testing positive for bird flu in October, a skunk tested positive for it in November, and a mountain lion that died in Gunnison County was recently confirmed to have the disease, said Travis Duncan with Colorado Parks and Wildlife.
All three of these cases showed signs of Highly Pathogenic Avian Influenza (HPAI) before or after death, he said. Other suspected mammalian cases have been detected in the state and are awaiting confirmatory testing.
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The black bear in Huerfano County was put down after a wildlife officer saw it having seizures and the decision to euthanize the animal was made with the knowledge that “numerous infectious diseases cause neurological symptoms,” according to CPW area wildlife manager Mike Brown.
The mountain lion that was found dead outside Gunnison city limits in mid-January had necrosis in the liver and bronchointerstitial pneumonia, which have been seen in domestic cats with HPAI, Duncan said.
While the recent spillover of H5N1 into other mammalian species has been reported in skunks, foxes, black bears, bobcats, coyotes, raccoons and even seals, “the number of mammal cases are currently low,” Duncan said.
So far, about 120 mammals have been infected with the H5N1 strain of avian influenza across the country, according to U.S. Department of Agriculture (USDA).
In Colorado, the most commonly affected wild birds have been geese, as well as the raptors and other scavenging birds that eat goose carcasses, CPW officials said.
“These mammals likely become infected by feeding on wild birds that are sick or have died of HPAI; however, not every mammal that consumes a sick bird will develop HPAI,” Duncan said.
What does this mean for humans?
While transmission of H5N1 from birds to people is very rare, it does happen, but this usually requires close and prolonged contact with infected birds.
Symptoms of bird flu in humans can range from no symptoms or mild illness (such as red eyes, fever, sore throat, cough, a runny nose, fatigue, etc.) to severe disease (pneumonia) and ultimately death, which has occurred in about 60% of people who've contracted H5N1, according to the World Health Organization.
Most bird flu virus infections can be treated with current flu antiviral drugs (such as Tamiflu) if treatment is started early after symptoms begin, according to the U.S. Centers for Disease Control and Prevention (CDC).
Wildlife officials continue to urge people to keep their distance from wildlife and to avoid handling sick or dead birds. Additionally, CPW urges people to contact their local office immediately if you happen to notice three or more dead birds in one area within a few weeks.
In Denver, people who encounter sickly or dead birds should call 311.
If you notice a dead bird on your own private property, be sure to wear gloves, a high-quality mask such as a KN95 or N95 respirator, and eye protection. Double bag the bird and throw it away in your municipal trash before thoroughly washing your hands.
For the latest updates on avian influenza cases and protocols in Colorado, head to the state's Department of Agriculture website.
