bThe sick flu has been hitting too close to home lately. In its testing of the commercial milk supply, the US Food and Drug Administration (FDA) reported on April 25 that 20% of milk samples tested at the retail market contained “viral fragments” of H5N1 avian flu. Many believe this is an understatement; experts at Ohio State University have found that as much as 40% of milk samples coming from processing facilities in the Midwest may contain parts of the virus.
The results immediately raised concerns about the safety of the U.S. milk supply and the risk of infection for people who consume it. So far, the U.S. Centers for Disease Control and Prevention (CDC) and the World Health Organization say the risk of people becoming infected from milk remains low. In the United States, there have only been two recent known cases of H5N1 in humans: one in a poultry worker in 2022 and another in March in a person who worked with dairy cows.
The situation is changing rapidly. But here’s what we know now about the risks of bird flu to the milk supply.
Is milk safe to drink?
The FDA says its testing found fragments of the virus, which does not mean that the viruses were alive and capable of infecting and causing disease. Agency scientists are conducting additional tests to determine whether the fragments are still infectious, which would help them decide whether drinking affected milk could lead to infection. “Early work by (National Institutes of Health)-funded researchers indicates an absence of infectious virus in their studies of retail milk,” the FDA said. saying on their website. “To date, retail milk studies have not shown results that change our assessment that the commercial milk supply is safe.”
Milk on store shelves is pasteurized, which generally kills viruses, and farmers have taken steps to discard milk from sick cows, the FDA says.
Read more: Is it safe to eat eggs and chicken during the bird flu outbreak?
Samuel Alcaine, associate professor of food sciences at Cornell University, is among scientists studying the virus in cows to understand how much virus infected animals have, how sick they get, and how infectious those viruses might be. if they reach milk or beef. (Cornell is part of the national network of laboratories that tests milk samples from sick cows.) Alcaine says pasteurization is designed to kill heat-sensitive pathogens, and recent research with eggs has shown that the process inactivates H5N1. “We have not done the complete studies in milk; “People are working on it right now,” he says. “But I’m pretty sure we’ll see this virus inactivated by heat.” At this point, I wouldn’t worry at all about buying milk at the grocery store. “I’m still doing that.”
What is the government doing to ensure milk is safe?
On April 24, the United States Department of Agriculture (USDA) issued a federal order requiring that all livestock be tested for the virus responsible for the current outbreak (H5N1 clade 2.3.4.4b) before moving from one state to another, in order to prevent spread to other stoves or installations. The agency also requests, but does not require, farmers to send milk from lactating cattle and nasal swabs from non-lactating cattle that become ill to the National Animal Health Laboratory Network for testing. And any state and veterinary laboratories that find positive tests must report them to the USDA Animal and Plant Health Inspection Service.
But even those measures may not be able to stop the spread of the virus, as it is unclear how many cows may be infected and asymptomatic (and therefore not have been tested). So far it appears that bird flu is milder in cows than in birds, where it can be fatal. “We’ve heard reports of cows showing essentially no signs of disease and testing positive,” says Andrew Bowman, associate professor of veterinary preventive medicine at Ohio State University. (Bowman was the scientist who conducted his own retail milk test and found that 40% of the samples had viral fragments.) “It’s one of those things we’re going to keep in mind; we can’t just rely on clinical signs to identify infected animals.”
Has H5N1 been found in beef?
Health officials are still investigating whether the virus is in beef, but Alcaine says so far it appears the virus is primarily found in the mammary glands of cows. “We’re still trying to understand how transmission occurs from one cow to another,” she says. “But it is not actually eliminated in the feces and it seems that the viral load is lower in the nasal cavity than in the mammary glands.” The same seems to be true for cow muscle. And it is unclear whether both male and female cows can be infected, as most tests so far have been done on milk-producing females.
How widespread is bird flu in livestock?
As of April 26, the USDA confirmed 34 outbreaks of bird flu in cattle in nine states. However, testing is relatively scarce, compared to the number of cattle in the US.
Why are health officials concerned about milk supply?
While the milk supply is currently believed to be safe, things could change quickly, health experts say.
They are watching how the virus jumps from one species to another and what genetic changes it detects as it makes these jumps. Avian flu strains are generally not suitable for infecting other species, including mammals. But the most recent case of bird flu in a person was also the first time the virus was found in cows.
The fact that it is now infecting cows (animals that people come into closer contact with than other mammals that have harbored H5N1, such as foxes) means that the viruses could be mutating in ways that could spread and cause disease. in a significantly larger number of people.
Bowman says the FDA report is concerning because it suggests that this particular strain of H5N1 continues to be transmitted among cows. “This is contagion to a mammalian host that seems to maintain (the infection),” she says. “In previous spreads to mammals, they seemed to be largely individual events that were isolated and did not continue to spread in those species. This is different.”
“Every time another animal or a human becomes infected, it’s another bet on the genetic roulette table in terms of whether the virus could be transmitted from human to human, which is what is required for a pandemic,” says Michael Osterholm. , director of the Center for Infectious Disease Research and Policy at the University of Minnesota. “If you throw enough times, you can end up with a result you don’t want.”
Read more: Experts can’t agree if we’re still in a pandemic
The biggest concern is if strains of avian influenza begin to appear in pigs. Pigs tend to be an effective vector of viruses from different species, which they then transmit to people, as their cells share common traits with other animals and humans. If that happens, then a human-compatible version of bird flu is more likely to reach people.
On farms, that scenario wouldn’t be a stretch, since cows and pigs often coexist there. USDA issued dairy workers guide Increase efforts to clean up milking equipment, spilled milk, clothing, vehicles and other animals that may come into contact with milk. The agency also warned that infected, unpasteurized milk could be a source of spread to other animals and potentially even people.
More testing is needed to determine if there is any risk of the virus spreading through airborne particles shed by infected animals. “The risk is not only respiratory from a breathing cow, but could also be in the aerosols created in the milking process itself,” says Osterholm.
That’s why the USDA also recommends that dairy workers wear personal protective equipment, such as masks and other body coverings, to limit their exposure to any viral particles.
At least for now, the danger to people remains low for the general public, Alcaine says. “The (infected) cows are recovering and seem to be producing milk again without problems,” she says. Still, “it will take some time to understand how it is affecting the dairy cow population.”