Just when you stopped hearing regularly about coronavirus (COVID-19) in the news, another infectious disease began dominating the headlines this spring: bird flu.
The good news is that — at least for now — public health experts don't see the latest bout of bird flu evolving into something resembling a coronavirus pandemic. But since the disease has spread to poultry in 48 states, dairy cattle in nine states, and two people in Texas and Colorado, you may be concerned about its potential impact on your health.
luck I spoke with three epidemiologists, who below answer important public health questions about bird flu.
What is bird flu?
The type of bird flu currently circulating is A Highly pathogenic avian influenza (HPAI)– A disease that can seriously infect wild and domestic birds, posing a major threat to the poultry industry and thus the global economy, according to the organization. United States Department of Agriculture (USDA). The other type, low-pathogenic avian influenza, causes mild infection in wild birds but can transform into highly pathogenic avian influenza in poultry.
Influenza viruses They are divided into four types, and are labeled A, B, C, and D Edwin Michael, Ph.Depidemiologist in 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 virus named after the proteins found on the surface of the virus.
“It can spread very quickly among wild birds. This could spread it all over the world,” says Michael. luck. “From birds, the virus is shed in mucus, saliva and feces, after which it can reach domestic poultry.”
When highly pathogenic avian influenza strains reach domestic poultry, they can kill entire flocks within days, the USDA says. Birds infected with HPAI may exhibit a wide range of symptoms including diarrhea, lack of energy and appetite, and decreased egg production. Since HPAI cannot be cured, culling poultry is the only solution.
He says such a cull could be effective in reducing the spread of birds that are vital to agriculture and food production in the United States Dr. William Schaffnerprofessor at Department of Infectious Diseases at Vanderbilt University Medical Center.
“This bird flu virus, in its various forms, has actually been around for a long time — more than a decade,” Schaffner says. luck. “It has been spreading gradually, but recently, somehow, for reasons that I do not understand in the least, its spread around the world has become more pronounced and more widespread.”
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How is bird flu transmitted to humans and other mammals?
Michael explains that the H5N1 virus is mutant, so to speak, because of its fragmented DNA.
“For example, if a human is infected with avian influenza virus and also carries human influenza A virus, these two viruses can exchange genetic material. This is known as Genetic transformation“This could form very new viruses (and) cause epidemics,” says Michael.
Michael says influenza pandemics are rare, occurring about three times a century. Perhaps the most notable is the so-called “Spanish Flu” 1918-1919when the Centers for Disease Control and Prevention (CDC) estimates that the “bird-like H1N1 virus” has killed 50 million people, and perhaps as many as 100 million, worldwide.
Maybe you remember 2009 swine flu pandemic, caused by a previously unknown H1N1 virus that contains genes from pigs, humans, and birds. How did this happen? Schaffner explains that because bird flu viruses don't always spread effectively between humans, they sometimes need help from other species to thrive.
“The pig’s respiratory system is set up in such a way that it can accept bird flu infection and-And“Infection with a human virus,” Schaffner says. “You can think of the pig as a test tube that avian influenza and human influenza are transmitted into, and if that happens simultaneously in the same pig, those two viruses come together and can have the ability to exchange genetic elements.”
While the latest strain of H5N1 is not known to be spreading among humans, it has already spread to more than a dozen species of land mammals, from black bears to bottlenose dolphins. On May 3, red foxes in New York and Michigan tested positive, according to USDA Animal and Plant Health Inspection Service (APHIS).
“This avian influenza virus is not dependent on pigs, but mutates on its own to become a more effective infection in a variety of different mammalian species,” Schaffner says. “The animal that was in the news was dairy cows, which surprised all the virologists.”
When did bird flu most recently appear in the United States?
Government agencies were monitoring Latest bird flu outbreaks Since January 12, 2022, when A Northern Shovel Ducks in Hyde County, North Carolina, have tested positive for the Eurasian strain of the H5N1 virus.
The disease spread everywhere among wild birds More than 1,100 counties As of May 8, 2024, it has infected approximately 9,400 birds.
The situation is worse in American poultry. As of May 7, there were approximately 91 million birds, including Commercial poultry and backyard flocks, had been injured. This includes more than 1,100 outbreaks in 522 counties across 48 states.
APHIS registered First infection of poultry At a commercial turkey flock in DuBois County, Indiana, on February 8, 2022.
Although the H5N1 virus has been spreading across the country among wild birds, domestic poultry and mammals since 2022, you may have only recently heard about it because of its impact. Jump to dairy cattle. The first positive case in Texas was documented on March 25, 2024.
As of May 7, there were approximately 40 herds of dairy cattle Infected across nine states.
Michael says the logistics of modern industrial farming may be why H5N1 spreads to livestock.
“Look at the density of animals on these farms, these are not natural places,” says Michael. luck. “So once you get (the infection), these things will spread very quickly among farm animals.”
Michael adds: “We have to shed light on how to do agriculture. That's the trade-off, you want the cheap meat and all the rest of it, but then you raise animals this way and you open the door to other things.
Is it safe to drink milk and eat chicken?
the Food and Drug Administration (FDA) He acknowledges that the presence of bird flu in dairy cows is a “new and evolving situation.” However, no previous studies have been conducted on the effects of pasteurization — a sterilization procedure that kills harmful bacteria — on bird flu in cow's milk. However, the FDA says current research has informed its understanding and conclusion that milk consumption is safe.
The U.S. Food and Drug Administration and USDA are conducting a national study of commercial milk samples, which includes formula-derived infant formulas. As of May 1, no HPAI has been detected in any of the combination products. While bird flu showed up in samples of milk, sour cream and cottage cheese, pasteurization inactivated the virus.
“We don't have to worry about milk, eggs and chicken as sources of infection,” Schaffner says. luck. “I'm over there drinking milk, and we had chicken last night for dinner.”
Both Schaffner and the FDA urge the public to stay away from raw, unpasteurized milk. The CDC recommends Cooking eggs and poultry To an internal temperature of up to 165 degrees to kill bacteria and viruses, including the H5N1 virus.
How concerned should you be about the impact of H5N1 on people?
Simply put, don't panic, he says Michael Osterholm, Ph.Dboss Center for Infectious Disease Research and Policy at the University of Minnesota.
“There is no evidence yet that this represents an imminent danger to humans,” Osterholm says. luck. “We have not seen it move into humans in a way that supports it will be the next pandemic virus.
“On the other hand, a rearrangement event, or ongoing mutations, could happen tomorrow.”
Two people have been infected so far with the H5N1 virus, according to the CDC. Someone exposed to dairy cows in Texas He tested positive on April 1, 2024, and A person in Colorado participates in poultry culling He 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, so having conjunctivitis is not unusual,” Osterholm says. He added: “There was no evidence of any type of respiratory infection, which is the primary factor for serious illness and therefore the ability to transmit the virus.”
This Texas case represents the first time a human has been infected with the H5N1 virus through contact with a mammal, according to the World Health Organization. Global Health Organization. However, the World Health Organization considers the public health risks to the general population to be low. For farmworkers and other industry employees potentially exposed to the virus, the risk is low to moderate.
Moving forward, ensuring the health and safety of agricultural workers is critical to preventing the spread of H5N1 to the broader population, Michael says.
“I don't think this is going to be a major outbreak (among humans),” Michael says. “(But) the risk is always there, always because of the way we manage nature.”
To learn more about the latest bird flu outbreaks:
