The U.S. will track bird flu infections in dairy cows headed for slaughter to understand how the virus infects meat. It will also test raw-milk cheeses to see if the virus is inactivated during the aging process.
The renewed focus on the U.S. food chain is the latest example of the fight against the contagious bird flu virus (H5N1), which has raised alarm bells around the world about the potential for a future pandemic.
Regulators will inspect 800 samples of dairy cows at slaughterhouses. Dairy cows are typically slaughtered when they no longer produce milk or otherwise retire, and they account for about 10% of US beef production, mostly in the form of ground beef.
The new cattle survey, which will start in mid-September, is representative of the entire country and will provide a clearer picture of the prevalence of the virus in meat from dairy cows. The survey can also provide insight into possible risks.
If a sample tests positive, the U.S. Department of Agriculture (USDA) will buy that carcass to conduct more experiments. Such studies could include whether the virus is viable — whether it can replicate in the lab — and determining the temperature that kills it.
An earlier study in May tested 109 muscle samples from cows that showed signs of illness after slaughter, and found H5N1 particles in one dairy cow. The animal was removed from the food supply. Another study sampled ground beef available in stores; none of the meat tested positive.
In another study, scientists pumped ground beef full of a fake virus and then cooked the meat. At 11 ounces, the burgers were thicker than what consumers would find at a fast-food restaurant, making them “very thick to make the worst-case scenario,” according to José Emilio Esteban, the USDA’s undersecretary for food safety.
But cooking them fully deactivated the virus, he said.
The virus was not detected at medium (145F/63C) and well done (160F/71C), internal temperatures long recommended by the USDA’s Food Safety and Inspection Service.
“If you cook it under those conditions, it should be very safe to eat,” Esteban said.
At 120F/49C, or less rarely, the imitation virus was “substantially inactivated” in burgers to which high levels of the virus had been added, the USDA said report say.
Cooking meat thoroughly helps eliminate all types of foodborne pathogens, said Kali Kniel, a professor of microbial food safety at the University of Delaware. “Consumers need to be aware of the potential for disease transmission and the control consumers have in their own kitchens,” she said.
But only about a quarter of Americans check the internal temperature of meat with a food thermometer, she said, a rate that is “not as high as anyone would like.”
Minced meat is usually bundled from several cowswhich increases the risk of foodborne illness if it is not fully cooked, she said.
“We know hamburgers are always riskier for those pathogens,” Kniel said. But “any virus particles would be inactivated with (full cooking) if there were any particles there at all. So not only are you going to kill the salmonella, you’re not going to have any risk of avian flu.”
The new meat research focuses only on dairy cows.
In experiments, scientists were able to infect young cows through their noses, but they believe the outbreak is spreading primarily among dairy cows drinking milk, through shared milking equipment and human intervention, the U.S. Department of Agriculture said.
It is not clear whether cattle have been tested for H5N1.
“If you start testing and looking for things, you might be able to find them,” Kniel said. But when it comes to food safety risks, she said, “I think we can control it with some behavioral changes and through the surveillance practices that are in place.”
The U.S. Food and Drug Administration (FDA) also announced Tuesday that continued testing has shown that pasteurization completely inactivates the bird flu virus in milk, making pasteurized milk safe to drink.
They looked at 167 dairy products, including butter and raw-milk cheese, that were available in stores in 27 states in June and July. About 17% of the products had inactivated virus particles, but none were viable, officials said.
Hard cheeses made from raw milk and then aged for at least 60 days do not contain traces of the virus, agency officials said, so they have not yet determined whether the aging process inactivates the virus.
“In the case of the raw milk cheese we tested, none of the samples in the study had viral genomic material, suggesting that the herd that produced the milk used to make the cheeses came from cows that were not infected at the time of milking,” said Steve Grube, chief medical officer for the FDA’s Center for Food Safety and Applied Nutrition. “Thus, no conclusions can be drawn about whether the production and aging of cheeses made from unpasteurized milk is sufficient to inactivate the virus.”
There is a revival of importance when drinking unpasteurized milk, which may contain deadly pathogens and has no advantages over pasteurized milk, during this outbreak.
Officials continue to warn that drinking raw milk is dangerous. “Raw milk consumption poses a risk to consumers,” Grube said.
That was long before the bird flu outbreak.
“It’s the one thing I always tell people: If there’s one thing you should avoid for foodborne illness, it’s raw milk,” Kniel said. Even cows that appear healthy can harbor pathogens that are deadly to humans. “The risk of consuming raw milk and getting sick from campylobacter, cryptosporidium, E. coli, listeria, salmonella — those are all really high risks.”
One cell of the Shiga toxin-producing E. coli can kill a person, and 100 salmonella cells can make a person sick for the rest of their life, she said.
It is not yet clear whether consuming raw milk can cause H5N1 infection, but it appears that some mammals may become infected this way. Mice fed H5N1-infected milk became ill quicklyand various barn cats that fed with milk of infected cows have died.
“We don’t know what the consumption of H5N1 through milk will do to people,” Kniel said.