Why are people worried now?

While most of the mammals that got sick from the virus seem to have eaten dead birds, it appears that minks on a farm in Spain and seals swimming off New England spread it to each other. No humans were infected in either outbreak, but the spread raised fears that the virus is getting better at moving between mammals.

The concern is that the way we raise animals in tightly packed facilities helps a virus to spread, giving it more chances to pick up mutations that would allow it to jump to humans, said Dr. Jon Samet, dean of the Colorado School of Public Health. While that hasn’t happened with this particular virus, there were cases where farmed minks caught the virus that causes COVID-19 and passed mutations on to their keepers, he said.

Avian influenza binds best to a receptor that’s very common in birds, but significantly less so in humans, Butcher said. For it to spread efficiently between humans, it would have to get better at attaching to receptors that are more common in our noses and throats, which hasn’t happened so far, he said.

The main way bird viruses could become better adapted to humans is if a pig were to be infected with both avian and human influenza, Butcher said.

Swine have receptors that overlap with both birds and humans, and if a pig were infected with both, the viruses could swap genes and gain the ability to infect the other species, he said. The same thing could happen if a person who was infected via direct contact with a bird also happened to have the seasonal flu.

“Anything is possible, but (the risk) is less than negligible,” he said.

It’s difficult to say exactly how high or low the risk of that kind of event is, Herlihy said. Public health officials can track incremental changes in a virus’s genes — like those seen in different variants of the virus that causes COVID-19 — but it’s harder to predict if an “unlucky” pig will get infected with two flu strains that swap genes, she said. The current theory is that the 2009 H1N1 flu was caused that way, with a pig getting infected with different swine flu viruses at the same time.

“There’s certainly always the potential for influenza to cause pandemics, but it’s really difficult for us to speculate,” she said. the virus without getting sick themselves. If you see a dead bird, don’t touch it, and notify your local Colorado Parks and Wildlife office if you see three dead birds in the same area within two weeks.

People should also try to avoid bringing bird feces home on their shoes or clothes, and keep their pets away from birds, the state health department said. Poultry owners should monitor their flocks for signs of illness, make sure wild birds can’t get into their flocks’ feed and take steps to shield poultry from wild birds’ feces, it said.

Sick poultry should be reported to the State Veterinarian’s Office.

People who have been exposed to sick or dead birds should monitor themselves for 10 days and call a health care provider if they develop a fever, difficulty breathing, cough, sore throat, runny or stuffy nose, body aches, headache or fatigue.

It’s generally a good idea to avoid contact with wildlife and keep your pets away from wild animals, but it’s especially so now that H5N1 is circulating in more bird species than is typical, Herlihy said.