Just when you stopped regularly hearing about COVID-19 in the news, another infectious disease began to dominate the headlines this spring: avian flu.
The good news is that public health experts (at least for now) don’t see this latest bird flu outbreak developing into anything like the coronavirus pandemic. But with the disease spreading to poultry in 48 states, dairy cows in nine, and two people in Texas and Colorado, you may be worried about its potential impact on your health.
Luck spoke with three epidemiologists who answer important public health questions about avian flu below.
What is bird flu?
The type of bird flu currently circulating is highly pathogenic avian influenza (HPAI)is a disease that can seriously affect wild and domestic birds, posing a serious threat to the poultry industry and therefore the global economy, according to US Department of Agriculture (USDA). Another type, low pathogenic avian influenza, causes mild infection in wild birds but can develop into HPAI in poultry.
Influenza viruses are divided into four types: A, B, C and D, explains Edwin Michael, Ph.D.epidemiologist University of South Florida College of Public Health. What we think of as seasonal influenza in humans is caused by types A and B. Bird flu falls under the category of influenza A viruses. The strain currently spreading in the United States is H5N1, HPAI, named for the proteins on the surface of the virus.
“It can spread very quickly among birds – wild birds. This could spread the disease around the world,” says Michael. Luck. “The virus is released from poultry in mucus, saliva, feces, and then can enter poultry.”
When HPAI strains reach poultry, they can kill entire flocks in a matter of days, according to the USDA. Birds with HPAI infection may exhibit a variety of symptoms, including diarrhea, lack of energy and appetite, and decreased egg production. Since HPAI has no cure, the only solution is to reduce the poultry population.
Such culling could be an effective means of limiting the spread of birds critical to U.S. agriculture and food production, says Dr. William Schaffnerprofessor in Division of Infectious Diseases, Vanderbilt University Medical Center.
“This particular avian influenza virus, in its variants, has actually been around for a long time—more than a decade,” Schaffner says. Luck. “It has gradually spread, but recently, somehow, for reasons that at least I don’t understand, its spread around the world has become much more noticeable and much more widespread.”
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How is bird flu transmitted to humans and other mammals?
H5N1 changes shape, so to speak, thanks to its segmented DNA, Michael explains.
“For example, if a person is infected with avian influenza and also carries the human influenza A virus, the two viruses can exchange genetic material. This is known as genetic shift– says Michael. “This can lead to the formation of completely new viruses. [and] cause epidemics.”
Flu pandemics, however, are rare and occur about three times a century, Michael says. Perhaps most notable is the so-called “Spanish Flu” 1918–1919when the Centers for Disease Control and Prevention (CDC) estimated that the “H1N1 avian virus” had killed 50 million and possibly 100 million people worldwide.
You probably remember 2009 swine flu pandemic, caused by a previously unknown H1N1 virus containing genes from pigs, humans and birds. How did this happen? Because avian influenza viruses do not always spread efficiently among humans, they sometimes require the help of other species to evolve, Schaffner explains.
— The respiratory tract of a pig is designed in such a way that it can transmit avian influenza infections and…And— infections with a human virus,” says Schaffner. “You can think of a pig as a test tube that gets avian and human flu, and if it happens at the same time in the same pig, then the two viruses come together and can exchange genetic elements.”
While it is unknown how the latest H5N1 strain spreads 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 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 different mammalian species,” says Schaffner. “What was in the news was the dairy cattle that surprised every virologist.”
When did bird flu last appear in the United States?
Government authorities are monitoring the situation recent bird flu outbreaks from January 12, 2022, when Northern shovel a duck in Hyde County, North Carolina, tested positive for the Eurasian strain H5N1.
Among wild birds, the disease has spread throughout the territory. more than 1100 counties as of May 8, 2024, approximately 9,400 birds are infected.
The situation is worse in bird USA. As of May 7, almost 91 million birds, including commercial poultry and backyard flocks, was infected. This covers more than 1,100 outbreaks in 522 counties in 48 states.
APHIS recorded first infection of poultry in a commercial turkey flock in Dubois County, Indiana on February 8, 2022.
Although H5N1 has been circulating across the country in wild birds, poultry and mammals since 2022, you may have heard of it more recently because of its virus. go to dairy cattle. The first positive case was reported in Texas on March 25, 2024.
As of May 7, about 40 herds of dairy cattle had been destroyed. infected in nine states.
The logistics of modern industrial agriculture may contribute to the spread of the H5N1 virus among cattle, Michael says.
“Look at the density of animals on these farms – these are not natural conditions,” says Michael. Luck. “So once you get [an infection]these things will spread very quickly among farm animals.”
Michael adds: “We need to shine a light on how farming is done. It’s a trade-off: you want cheap meat and all that, but then you raise the animals that way and open the door to other things.”
Is it safe to drink milk and eat chicken?
Food and Drug Administration (FDA) acknowledges that the presence of avian influenza in dairy cows is a “new and evolving situation.” However, there have been no previous studies on the effect of pasteurization (a sterilization measure that kills harmful bacteria) on HPAI in cow’s milk. However, the FDA states that existing research has led to the understanding and conclusion that milk consumption is safe.
The FDA and USDA are conducting a national commercial study of milk samples that includes infant formulas derived from milk. As of May 1, HPAI has not been detected in any infant formula. Although avian influenza was found in samples of milk, sour cream and cottage cheese, pasteurization inactivated the virus.
“No need to worry about milk, eggs, [and] chicken as a source of infection,” says Schaffner. Luck. “I drink milk there, and last night we had chicken for dinner.”
Both Schaffner and the FDA urge the public to stay away from raw, unpasteurized milk. The Center for Disease Control and Prevention recommends cooking eggs and poultry to an internal temperature of 165 degrees to kill bacteria and viruses, including H5N1.
How concerned should you be about the H5N1 virus affecting people?
Simply put, don’t panic, says Michael Osterholm, Ph.D.director Center for Infectious Disease Research and Policy at the University of Minnesota.
“There is no evidence at this time that this poses an immediate risk to people,” Osterholm says. Luck. “We haven’t seen it jump into people in a way that would suggest it will be the next pandemic virus.
“On the other hand, a reassortant event or continuation of mutations could happen tomorrow.”
So far, two people have been infected with H5N1, according to the CDC. Person exposed to dairy cattle in Texas tested positive on April 1, 2024, and man in Colorado culling poultry positive test result on April 28, 2022. Human-to-human transmission has not been confirmed, and in a more recent patient the only symptom was conjunctivitis or pink eye.
“There are two or three receptor sites in our eyes, so a case of conjunctivitis would not be considered unusual,” says Osterholm. “There was no evidence of any respiratory infection, which is a key factor in severe illness and subsequent transmission of the virus.”
According to the organization, the case in Texas was the first case of human infection with H5N1 through contact with a mammal. World Health Organization (WHO). Despite this, WHO considers the risk to public health to be generally low. For farmworkers and other industry employees who may be exposed to the virus, the risk is low to moderate.
Going forward, ensuring the health and safety of farmworkers is paramount to preventing the spread of the H5N1 virus to the wider population, Michael said.
“I don’t think this outbreak will become large (among people),” Michael says. “[But] the risk is always, always there because of how we manage nature.”
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