The US will track bird flu infections in slaughtered dairy cows to understand how the virus infects meat and will also continue to test raw milk cheeses to see if the virus is inactivated in the aging process.
The renewed focus on the US food chain is the latest front in the effort to combat the highly contagious bird flu virus, or H5N1, which has set off alarm bells around the world as a potential future pandemic.
Regulators will inspect 800 samples of dairy cows in slaughterhouses. Dairy cows are usually slaughtered when they no longer produce milk or otherwise retire, and they make approx 10% of beef production in the US, typically as ground beef.
The new cattle survey, which will start in mid-September, will be nationally representative to give a clearer picture of how widespread the virus is in meat from dairy cows, and it can also provide insight into potential risks.
If a sample tests positive, the US Department of Agricultural (USDA) will purchase that carcass to conduct more experiments. Such studies may include whether the virus is viable – whether it can replicate in the laboratory – and determining the temperature at which it is killed.
An earlier survey in May tested 109 muscle samples from cows that showed signs of disease after slaughter, and they found H5N1 particles in one dairy cow. The animal was kept out of the food supply. Another survey sampled 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. Weighing in at 300g, the burgers were thicker than what consumers might find in a fast-food restaurant, making them “very thick to make it the worst-case scenario”, said José Emilio Esteban, USDA’s undersecretary for food safety.
But cooking them fully deactivated the virus, he said.
At medium (145F/63C) and well done (160F/71C), the virus was not detected. Those internal temperatures have long been 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 barely, the mock virus was “substantially inactivated” in burgers with high levels of virus added, the USDA report say.
Fully cooking meat helps eradicate all types of foodborne pathogens, said Kali Kniel, 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 just about one 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.”
Ground meat is usually combined from several cowswhich increases the risks of foodborne illness when it is not fully cooked, she said.
“We know that citizens are always more at risk for those pathogens,” Kniel said. But “all virus particles would be inactivated with [cooking fully] if there would be any there. So not only will you kill the salmonella, you will have no risk of bird flu.”
The new study on meat will only focus on dairy cows.
In experiments, scientists have been able to infect young cows through their noses, but they believe the outbreak seems to be moving mainly among lactating dairy cows through shared milking equipment and human interventionsays the USDA.
It is not clear whether any beef cattle have been tested for H5N1.
“If you start testing and looking for things, you might find them,” Kniel said. But as for food safety risks, she said, “I think we are able to control it with certain behavioral changes and through the surveillance practices that are in place.”
The US Food and Drug Administration (FDA) also announced on Tuesday that ongoing testing has shown that pasteurization fully inactivates the bird flu virus in milk, making the pasteurized milk supply safe to drink.
They looked at 167 dairy products, including butter and raw-milk cheese, available in stores in 27 states in June and July. About 17% of the products had inactivated viral particles, but none of them were viable, officials said.
Hard cheeses made from raw milk and then aged for at least 60 days had no traces of the virus, agency officials said — so they could not yet determine whether the aging process inactivates the virus.
“In the case of the raw milk cheeses we tested, none of the samples in the study had viral genomic material, suggesting that the herd that produces the milk used to prepare the cheeses is from cows was not contaminated at the time of milking,” said Steve Grube, chief medical officer for the FDA’s Center for Food Safety and Applied Nutrition. “Therefore, no conclusions can be drawn as to whether the production and aging of cheeses made from unpasteurized milk is sufficient to inactivate the virus.”
There was a take off of importance in drinking unpasteurized milk, which can carry deadly pathogens and has no benefit over pasteurized milk, during this outbreak.
Officials still warn that drinking raw milk is dangerous. “Consuming raw milk does pose a risk to consumers,” Grube said.
This was true long before the bird flu outbreak.
“That’s the one thing I always tell people: if there’s anything to avoid because of foodborne illness, it’s definitely raw milk,” Kniel said. Even cows that appear healthy can harbor pathogens that are deadly to humans. “The risk of consumption of raw milk and diseases related to campylobacter, cryptosporidium, E coli, listeria, salmonella – these are all very high risks.”
One cell of Shiga toxin-producing E coli can kill a person, and 100 cells of salmonella can make someone sick for the rest of their life, she said.
It is not yet clear whether consumption of raw milk can cause H5N1 infection, but it appears to infect some mammals in this way. Mice fed H5N1-infected milk quickly fell illand several shed cats that fed on milk died from infected cows.
“We don’t know what consuming H5N1 in milk is going to do” in humans, Kniel said.
