Is the US prepared for a possible bird flu pandemic? What we know.

As health officials continue to track and manage one of the largest bird flu outbreaks in recorded history, the virus is beginning to spill over into mammals – including humans.

While human infections are still few and far between, health experts say it only takes one perfect combination of mutations for the virus to cause widespread transmission among the human population.

“There’s a tremendous amount of uncertainty about what is currently happening with bird flu and what might happen in the future,” said Dr. Jay Varma, director of Cornell University’s Center for Pandemic Prevention and Response.

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Tracking avian influenza: How widespread is it?

Bird flu has been on officials’ radar since the late 1990s, health experts say.

The strains causing widespread outbreak now – avian influenza A (H5N1) viruses – first arose in 2020 and spread via migratory birds to Africa, Asia and Europe, according to the World Health Organization.

In late 2021, the H5N1 strains crossed to North America. The U.S. Department of Agriculture reports over 58 million chickens have been affected in 47 states. Nearly 6,200 wild birds have been infected including eagles, hawks, geese and ducks, as of this week.

“It seems like it spreads very easily among different bird species. You have so many different bird species that die off so rapidly from it,” said Varma, who is also the chief medical adviser at Kroll, a risk consulting firm.

Health experts, however, are more concerned with how the virus is affecting mammals. The USDA has detected H5N1 in various animals all over the country including skunks, foxes, raccoons, bears, mountain lions and dolphins, among others.

Most of these infections appear to be individual cases where the animal may have gotten sick from eating an infected bird, experts say.

Mammalian transmission: Why experts are concerned

However, two instances of possible mammalian transmission have rung alarm bells for health experts.

Between June and mid-July, over 150 dead seals in Maine were attributed to the bird flu, according to the National Oceanic and Atmospheric Administration. Although it’s possible the seals could have eaten infected birds, health experts say the large number of dead seals and their proximity to one another suggests mammal-to-mammal transmission.

Another outbreak on a Spanish mink farm suggests the virus may have adapted to mammal transmission. Scientific investigators were called when minks began showing signs of infection including loss of appetite, hypersalivation, depression, bloody snout and tremors.

After swabbing two infected animals, they determined the rest of the sickened minks had bird flu. It’s unclear exactly how many minks were infected, but researchers noted the animals began dying a few days after exhibiting symptoms.

More than 51,000 minks were killed to prevent further spread. Post-mortem examination of infected minks found pneumonia in their lungs. This also sounded the alarm for health experts, who say a mink's respiratory tract is closer to that of a human than bird.

"Ferrets, which are close relatives of mink, are our best animal model for human influenza infection," said Stephen Morse, a professor epidemiology at Columbia University's Mailman School of Public Health. "So, finding natural infection in mink seems a step closer to potentially infecting humans."

After sequencing the offending strain, researchers discovered the H5N1 had a slight mutation that doesn't exist in strain affecting birds. This "uncommon" mutation – T271A in the PB2 gene – was also seen in the swine flu H1N1 virus responsible for the 2009 pandemic that the CDC estimates caused more than 12,000 deaths in the U.S.

“We worry that this might be the prelude to the virus mutating in such a way that becomes a human epidemic," Varma said.

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Can humans get bird flu? How does it spread to humans?

As of December, the WHO has reported six human infections from the circulating bird flu strains in China, Spain, the U.K., the U.S. and Vietnam.

All four cases in the U.S. and Europe were asymptomatic or mild infections, with fatigue reported as the only symptom. The patient in Vietnam developed severe disease but recovered, while the patient in China died.

“So far, the virus is difficult to transmit between people and the overwhelming majority of cases have been in people who have in direct and close contact with birds,” said Dr. Hana El Sahly, professor of molecular virology and microbiology at Baylor College of Medicine.

Bird flu tends to infect the lower respiratory tract, showing “it has a preference” in the lungs, said Dr. Katherine Baumgarten, medical director for infection control and prevention at Ochsner Health.

This suggests it could be less transmissible between humans because not as many viral particles are concentrated in the upper respiratory tract, like the nose or mouth, she said. But it also suggests the virus may be more capable of causing severe disease.

Can avian influenza cause a human pandemic?

Although researchers have identified certain mutations that may be associated with mammalian adaptation, health experts say these genes don’t seem to support widespread transmission between animals.

But that doesn’t mean it can’t happen. The more virus spreads, the more opportunities it gets to mutate and adapt.

“Flu viruses are always evolving, making them very unpredictable,” Morse said. “Could it spill over to the human population, and could it eventually become a pandemic? We really can’t say. It’s possible, but we don’t know how likely or, if it happens, when.”

Government agencies and international organizations track and study cases among birds, mammals and humans to detect any abnormalities that would be a cause for concern.

Health experts say it’s important to prepare for the possibility of an H5N1 pandemic because humans don’t have any immunity to the virus and it’s likely to cause severe disease.

Is the US ready for a bird flu pandemic?

In addition to surveillance, health experts say the U.S. needs vaccines, treatments and personal protective equipment to prevent spread.

The United States has antivirals for the seasonal influenza virus – the most widely used is known by its brand name Tamiflu – but health experts say it’s unclear if those will work against the circulating H5N1 strains.

A vaccine for H5N1 has been approved by the Food and Drug Administration for people 18 through 64 years who are at increased risk of exposure, according to an agency spokesperson.

The country has a small supply of vaccine, a spokesperson from the Health and Human Services told USA TODAY. The vaccine can be used to match against strains with pandemic potential and scale-up as needed, which health experts estimate could take up to six months.

About 100 public health laboratories across the country are also equipped with testing that can detect H5 viruses or novel influenza A viruses, according to the CDC.

Even if testing wasn't available, a CDC spokesperson told USA TODAY that most commercial testing for the seasonal flu would be able to detect a new influenza A virus should an outbreak occur.

How to protect yourself against the bird flu

To prevent infection, the CDC recommends avoiding unprotected contact with wild or domesticated birds that may look sick or have died. If contact can't be avoided, the agency recommends:

  • Wearing personal protective equipment, like disposable gloves, boots, an N95 mask and eye protection.

  • Avoid touching your mouth, nose or eyes during and after contact with birds or contaminated surfaces.

  • Wash your hands with soap and water.

  • Change your clothes after contact.

Follow Adrianna Rodriguez on Twitter: @AdriannaUSAT.

Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.

This article originally appeared on USA TODAY: Bird flu in humans: Is avian influenza the next pandemic? What to know