Bird flu is spreading across the U.S. How worried should you be?

From COVID, the flu and monkeypox to West Nile and eastern equine encephalitis, public health officials are currently watching a lot of viruses. You can now add “bird flu” to that list.

Avian influenza is not spreading from person to person, but health officials are sounding the alarm. A new strain that was first detected in 2020 and has spread faster and wider across the globe than ever before has public health officials worried that another pandemic could emerge.

The virus, first identified among people in Hong Kong in 1997, has “been around a long time,” said Lauren Kallins, senior legislative director for health and human services policy at the National Conference of State Legislatures, during a webinar on the subject last week. “But what is concerning about the current outbreak is that it is a highly contagious variety of avian flu that has infected previously uninfected species, including, for the first time, dairy cows.” 

When viruses start behaving differently, said Dr. Jay Butler, senior advisor for infectious diseases at the Centers for Disease Control and Prevention, that’s a concern for public health officials because infections that initially didn’t easily transfer between humans could evolve to do so.

“The more opportunities we give for this virus to jump into people, the more we have the potential for a human-adapted virus to cause a pandemic,” said Maggie Baldwin, state veterinarian at the Colorado Department of Agriculture.

The first infection of a cow in the U.S. was detected in March on a dairy farm in Texas. Since then, bird flu has spread across 299 dairy cattle herds across 14 states, and as of Oct. 11, has infected almost 19 million birds across commercial and backyard flocks in nearly every state, according to the CDC.

Human infections remain rare, but the CDC has reported that 20 people have been infected as of last week. Most of those people contracted bird flu from dairy animals or poultry, although Kallins said in one of the confirmed cases, the person had no known contact with an infected animal.

In Missouri, public health officials confirmed a human case of bird flu in September in an adult patient who was hospitalized the month prior. At least seven health workers who came into contact with the person have reported experiencing respiratory symptoms.

An ongoing investigation conducted by the Missouri Department of Health and Senior Services has yet to determine the risk of human-to-human transmission. CDC officials are also evaluating antibody tests from the health care workers, Butler said, “but the bottom line at this time is we have not confirmed any human-to-human transmission.”

That means the public health risk of bird flu “remains low,” he said. “However, the risk for people with close or prolonged, and particularly unprotected, exposure to infected animals or to environments contaminated by infected animals is higher.”

Federal health officials have also reported that the risk of bird flu being transmitted to humans through cow milk is low, particularly for pasteurized milk products, said Dr. Steven Grube, chief medical officer at the U.S. Food and Drug Administration’s Center for Food Safety and Applied Nutrition

To guard against further spread of the virus, Butler says the CDC recommends that health officials encourage those who work closely with animals, particularly cows and birds, to wear personal protective equipment. He also says people should closely monitor their symptoms after coming into contact with animals for 10 days.

But most of the focus should be on preventing the spread in animals. 

Testing animal byproducts is a crucial way public health officials can manage and monitor bird flu infections, Colorado's Baldwin said. Previously when testing was voluntary in the state, there was low uptake among dairy facilities, but as public health officials observed that cow infections had a spillover effect on poultry sites, bird flu testing became mandatory among dairy cow sites.

In July, for example, the state agency started requiring licensed dairy cow facilities to submit bulk milk samples weekly to the Department of Public Health and Environment for bird flu testing. If samples come back positive, Baldwin said the cattle herds are quarantined until they produce two negative tests.

Dairy farmers have also been required to test cattle before transporting them across state lines since April to help prevent the spread of bird flu.

There are nearly 90 dairy cow premises in Colorado, Baldwin said, and since the safety guidelines were established, roughly 60 of them have been subjected to and released from quarantine.

In Iowa, the leading egg-producing state in the U.S., managing bird flu among poultry populations requires a more stringent response because the infection is much more fatal among birds than cattle, said Jeff Kaisand, state veterinarian at the Iowa Department of Agriculture and Land Stewardship.

State health officials in May reported that a lock of more than 4 million chickens in Iowa would be killed in order to stop the spread of bird flu. The move encourages farmers to more closely adhere to safety and testing requirements in the future to prevent the loss of production, Kaisand said.

“You can eliminate the industry while eliminating the disease,” he said, “but we can’t let the disease eliminate the industry.”