New Human Cases of Avian Flu Anticipated

With avian influenza spreading quickly around the globe, the virus has more opportunities to mutate and cause problems for people. By some calculations, H5N1 bird flu is still at least two mutations away from widespread human infections, but experts warn that new flu symptoms in individuals at high risk are likely to start turning up in health systems this summer.

“There is a broad range of symptoms to be watching for,” said Vivien Dugan, PhD, director of the influenza division at the US Centers for Disease Control and Prevention (CDC). “Some of this will not be obvious or at the forefront of our minds.”

Dugan is leading the team of CDC scientists that is working with partners from the US Department of Agriculture, the US Food and Drug Administration (FDA), and state and local health departments to track and respond to the H5N1 bird flu outbreak currently sweeping through the US.

Since 2022, avian influenza A viruses have been detected in more than 9300 wild birds in 50 states and territories and in commercial and backyard flocks.

“It’s a bad situation,” said Florian Krammer, PhD, professor of vaccinology at the Icahn School of Medicine at Mount Sinai in New York. “Globally, we’ve seen tons of exposure in cities around the world and even in the birds here in New York City where I am.”

Birds shed the virus in their saliva, mucous, and feces, so people or other animals with close, unprotected contact with infected birds or their contaminated environments can be infected. 

And for the first time in March 2024, H5N1 bird flu was reported in dairy cows. The US Department of Agriculture said that at last count 101 dairy herds in 12 states had been infected, with several cases also found in dairy workers.

From Birds to Cattle and Farm Workers

The National Veterinary Services Laboratories confirmed the infections were highly pathogenic avian influenza H5N1 clade 2.3.4.4b of Eurasian lineage. Also known as the goose, Guangdong clade from China, phylogenetic analysis and epidemiology suggests a single introduction into cows followed by onward transmission.

“I was surprised when H5 was introduced to dairy cattle in this way,” Dugan said during an interview. “Influenza viruses are always surprising us and it reminds me to stay humble and keep an open mind when dealing with them.”

People rarely inhale or get sufficient virus in their eyes or mouth to get sick, Dugan said, but those in close contact with animals are still at risk for infection, which could lead to upper respiratory tract symptoms such as shortness of breath, cough, sore throat, or runny or stuffy nose.

Like with other viruses, people can also experience muscle or body aches, headache, fatigue, fever or, as was seen in farm workers, conjunctivitis.

But there are less-common symptoms too like diarrhea, nausea, and vomiting — and sometimes, even seizures.

The risk to the general public is still low, Dugan said, but authorities recommend that people working with animals wash their hands with soap and water and wear personal protective equipment that includes fluid-resistant coveralls, a waterproof apron, a safety-approved respirator, properly fitted goggles or face shield, a head or hair cover, gloves, and boots.

Dugan said that healthcare providers often don’t take a history of occupational exposures when a patient presents with flu. But with rising rates of bird flu in new animal hosts, “this will be an important next step.”

Asking Unusual Questions

This approach is not standardized on most electronic health records, so these are questions that clinicians will need to initiate themselves.

“Physicians should ask about work,” said Meghan Davis, PhD, associate professor at the Johns Hopkins Bloomberg School of Public Health in Baltimore. “If it’s not already on the radar, asking about any direct contact with dairy cows, poultry, pigs, wild birds or wild mammals is important.”

Davis says she’s worried about a new study tracking risk factors for farm-to-farm transmission because it shows that farms testing positive for avian influenza often have workers with a family member also employed on another farm. “This suggests that we might need to be on the lookout for possible transmission within families,” she said. Now, we have to ask “not just if the person with symptoms has contact with or works on a dairy farm, milk processing plant, or slaughterhouse, but also if any family member does.”

Davis said that it’s important to bear in mind when taking these histories that there may be younger workers on farms and in slaughter and processing facilities due to exemptions or illegal work.

What is important now is to get the situation under control this season in dairy cattle, Krammer said. “This will be easier to stop in cows than humans, so this is the time to stop moving dairy cattle and start vaccinating them.”

Spotting New Cases

Since April 2024, there have been three human cases of avian influenza after exposure to dairy cows reported. “And what we don’t want to see this summer is an unusual human cluster of influenza. It’s important we keep a close, watchful eye for this,” Krammer said.

“Influenza viruses do very interesting things and as we head into fall and winter flu season, we don’t want new human co-infections that could cause major problems for us,” he said.

If people become mixing vessels of a seasonal cocktail of multiple viruses, that could empower H5N1 to mutate again into something more dangerous, sparking a new pandemic.

“It wasn’t all that long ago that we were asking China difficult questions about the steps Chinese authorities took to protect human lives from SARS-CoV-2 in the COVID pandemic. Now, we must ask ourselves many of these questions,” Krammer said. “We are at a crucial crossroad where we will either elude a new pandemic or see one take off, risking 10 to 20 million lives.”

There is a precedent for safely evading more trouble, Krammer pointed out. Government agencies have already been working with the poultry industry for a couple of years now. “And here, we have successfully stopped H5N1 with new regulations and policies.”

But moving from poultry farms to cattle has not been an easy transition, Dugan said. Cattle farms have no experience with bird flu or tactics to contain it with regulations, and officials too are working in new, unfamiliar terrain.

“What we have now isn’t a science problem, it’s a policy issue, and it hasn’t always been clear who is in charge,” Krammer said.

“Agencies are working together at the state, federal, and global level,” said Dugan. “We are increasing our transparency and are working to share what we know, when we know it.”

The infrastructure built during the COVID pandemic has helped teams prepare for this new crisis, Dugan said. Year-round, layered monitoring has clinical labs reporting seasonal influenza and novel cases.

“Laboratories are ready to help with testing,” Dugan said.

Specimens should be collected as soon as possible from patients with flu symptoms. A nasopharyngeal swab is recommended with a nasal swab combined with an oropharyngeal swab. If a patient has conjunctivitis with or without respiratory symptoms, both a conjunctival swab and a nasopharyngeal swab should be collected. 

People with severe respiratory disease should also have lower respiratory tract specimens collected.

Standard, contact, and airborne precautions are recommended for patients presenting for medical care who have illness consistent with influenza and recent exposure to birds or other animals.

Antiviral Drugs

There are four FDA-approved antivirals for influenza:

For people with suspected or confirmed avian influenza, treatment is recommended as soon as possible. 

There are no clinical trials measuring the outcome of antivirals in people infected with avian influenza. However, data from animal models and human observational studies suggest a benefit.

“We can’t afford to wait this summer,” Krammer said. “We have an opportunity right now to stop this in cows before we risk infecting more people. I hope we do.”