Just when we stopped hearing about COVID-19 regularly in the news, another infectious disease began making headlines this spring: avian flu.
The good news is that, for now at least, public health experts do not see this latest bird flu crisis evolving into a bird flu-like situation. corona virus pandemic. But given that the disease has spread to poultry in 48 states, to dairy cows in nine, and to two people in Texas and Colorado, you may be concerned about its potential impact on your health.
Fortune spoke with a trio of epidemiologists, who answer critical public health questions about bird flu.
What is bird flu?
The type of avian flu currently circulating is a highly pathogenic avian influenza (HPAI)—a disease that can seriously sicken wild and domestic birds, posing a major threat to the poultry industry and therefore to the global economy, according to the United States Department of Agriculture (USDA). The other type, low pathogenic avian influenza, causes mild infection in wild poultry but can develop into HPAI in poultry.
Flu virus are divided into four types, A, B, C and D, explains Edwin Michael, Ph.D.epidemiologist at University of South Florida College of Public Health. What we consider seasonal influenza in humans is caused by types A and B. Avian influenza falls under the umbrella of influenza A viruses. The strain currently spreading in the United States is H5N1, an HPAI named for the proteins present on the surface of the virus.
“It can spread very quickly through the wild bird population. This can spread all over the world,” says Michael. Fortune. “From the bird, the virus is excreted in mucus, saliva, feces, which can then enter domestic poultry.”
When HPAI strains reach domestic poultry, they can kill entire flocks within days, according to the USDA. Birds infected with HPAI may exhibit many symptoms, including diarrhea, lack of energy and appetite, and decreased egg production. Because HPAI cannot be treated, culling poultry is the only solution.
Such culling can be effective in curbing the spread of birds essential to U.S. agriculture and food production, according to Dr. William Schaffnerprofessor at Vanderbilt University Medical Center Division of Infectious Diseases.
“This particular avian flu virus, in its variants, has actually been around for a long time, more than a decade,” says Schaffner. Fortune. “It spread gradually, but recently, for reasons I don’t understand, its spread across the world has become much larger and more widespread.”
DIGICOMPHOTO/SCIENCE PHOTO LIBRARY VIA GETTY IMAGES
How is bird flu transmitted to humans and other mammals?
H5N1 is a shapeshifter, so to speak, due to its segmented DNA, Michael explains.
“For example, if a human is infected with avian influenza and also carries the human influenza A virus, these two viruses can exchange genetic material. That’s what we call genetic change“, says Michel. “This can form very new viruses (and) cause epidemics.”
Flu pandemics, however, are rare and occur about three times a century, Michael explains. Perhaps the most notable is the so-called “Spanish flu” of 1918-1919while the Centers for Disease Control and Prevention (CDC) estimates that “an avian-type H1N1 virus” has killed 50 million, and perhaps as many as 100 million, people worldwide.
You probably remember the 2009 swine flu pandemic, caused by a previously unknown H1N1 virus that contained porcine, human and avian genes. How did it happen? Because avian flu viruses don’t always spread efficiently between humans, they sometimes need help from other species to thrive, Schaffner says.
“The pig’s respiratory tract is configured in such a way that it can accept avian flu infections and…And– infections with a human virus,” explains Schaffner. “You could think of the pig as a test tube into which a bird flu and a human flu enter, and if this happens simultaneously in the same pig, then these two viruses come together and may have the ability to exchange elements genetics.”
Although the latest H5N1 strain is not spreading among humans, it has already spread to more than a dozen species of wild mammals, from black bears to bottlenose dolphins. As recently as May 3, red foxes in New York and Michigan tested positive, according to the USDA Animal and Plant Health Inspection Service (APHIS).
“This avian flu virus does not attack pigs but mutates on its own to become a more effective infection in various mammal species,” explains Schaffner. “The one that made the news was that of dairy cattle, which surprised all the virologists.”
When did bird flu last appear in the United States?
Government agencies monitor latest bird flu outbreaks since January 12, 2022, when a Northern Shoveler duck in Hyde County, North Carolina, tested positive for a Eurasian strain of H5N1.
Among wild birds, the disease has spread everywhere more than 1,100 counties as of May 8, 2024, infecting nearly 9,400 poultry.
The situation is worse in American poultry. As of May 7, nearly 91 million birds, including commercial poultry and backyard flocks, had been infected. This encompasses more than 1,100 outbreaks in 522 counties in 48 states.
APHIS recorded the first infection of poultry in a commercial turkey flock in Dubois County, Indiana on February 8, 2022.
Although H5N1 has been circulating nationwide in wild birds, domestic poultry, and mammals since 2022, you may have only recently heard about it due to its switch to dairy cattle. The first positive case was documented in Texas on March 25, 2024.
As of May 7, nearly 40 herds of dairy cattle had been infected in nine states.
The logistics of modern industrial agriculture could fuel the spread of the H5N1 virus to livestock, Michael says.
“Look at the density of animals on these farms: these are not natural environments,” explains Michael. Fortune. “So as soon as you get (an infection), these things spread very quickly among farm animals.”
Michael adds: “We need to shed light on how agriculture is done. That’s the trade-off, you want cheap meat and everything else, but then you raise animals that way and you open the door to other things.
Is it safe to drink milk and eat chicken?
THE Food and Drug Administration (FDA) recognizes that the presence of avian influenza in dairy cows is “a new and evolving situation”. That said, no previous studies have been done on the effects of pasteurization – a sterilization measure that kills harmful bacteria – on HPAI in cow’s milk. However, the FDA says existing research has informed its understanding and conclusion that milk consumption is safe.
The FDA and USDA are conducting a national sampling study of commercial milk, which includes milk-derived infant formula. As of May 1, no HPAI had been detected in infant formula. While bird flu appeared in samples of milk, sour cream and cottage cheese, pasteurization inactivated the virus.
“There is no need to worry about milk, eggs (and) chicken as sources of infection,” says Schaffner. Fortune. “I drink milk and we had chicken last night for dinner.”
Schaffner and the FDA urge the public to avoid raw, unpasteurized milk. The CDC recommends cooking eggs and poultry at an internal temperature of 165 degrees to kill bacteria and viruses, including H5N1.
How concerned should you be about H5N1 affecting people?
Simply put, don’t panic, says Michael Osterholm, Ph.D.director of University of Minnesota Center for Infectious Disease Research and Policy.
“There is no evidence at this point that this is an imminent risk to humans,” Osterholm said. Fortune. “We haven’t seen it transmit to humans in a way that would suggest it’s going to be the next pandemic virus.
“On the other hand, a reassortment event, or continued mutations, could occur tomorrow.”
So far, two humans have caught the H5N1 virus, according to the CDC. Person exposed to dairy cattle in Texas tested positive on April 1, 2024, and Colorado person involved in poultry slaughter tested positive on April 28, 2022. No human-to-human transmission has been confirmed and the most recent patient’s only symptom was conjunctivitis or pink eye.
“We have two or three receptor sites in our eyes, and so having a case of conjunctivitis would not be considered unusual,” says Osterholm. “There was no evidence of any respiratory infection, which is the key to serious illness and the ability to transmit the virus.”
This Texas case marks the first time a human has been infected with H5N1 through contact with a mammal, according to the World Health Organization (WHO). Nevertheless, the WHO considers the public health risk to the general population to be low. For farmworkers and other industry personnel who may be exposed to the virus, the risk is low to moderate.
Going forward, ensuring the health and safety of agricultural workers is paramount to preventing H5N1 from spreading to the general population, says Michael.
“I don’t think this will be a major outbreak (in humans),” Michael says. “(But) the risk is always, always there because of the way we manage nature.”
To learn more about the latest bird flu outbreak:
