The US will track bird flu infections in dairy cows brought to slaughter to understand the ways the virus infects meat and will also continue testing raw milk cheeses to see whether the virus is inactivated in the ageing process.
The renewed focus on the US food chain is the latest front in the effort to combat the infectious bird flu virus, or H5N1, which has triggered alarm bells across the world as a potential future pandemic.
Regulators will inspect 800 samples from dairy cows in slaughterhouses. Dairy cows are usually slaughtered when they no longer produce milk or otherwise retire, and they account for about 10% of beef production in the US, typically as ground beef.
The new cattle survey, set to begin 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 could also offer insight into potential risks.
If a sample tests positive, the US Department of Agriculture (USDA) will purchase that carcass in order to conduct more experiments. Such studies could include whether the virus is viable – whether it can replicate in the lab – and determining the temperature at which it is killed.
An earlier survey in May tested 109 muscle samples from cows that showed signs of illness after slaughter, and they found H5N1 particles in one dairy cow. The animal was kept out of the food supply. Another survey sampled ground beef available in stores; none of the meat tested positive.
In another study, scientists pumped ground beef full of an imitation virus and then cooked the meat. Weighing in at 300g, the hamburgers 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 under-secretary for food safety.
But cooking them fully did inactivate 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 rare, the imitation virus was “substantially inactivated” in burgers with high levels of virus added, the USDA report says.
Cooking meat fully helps eradicate all kinds of foodborne pathogens, said Kali Kniel, professor of microbial food safety at the University of Delaware. “Consumers need to be cognizant of the potential for disease transmission and the control consumers have in their own kitchens,” she said.
But only 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 beef is usually pooled from multiple cows, increasing the risks of foodborne illness when not fully cooked, she said.
“We know that burgers are always more risky for those pathogens,” Kniel said. But “all virus particles would be inactivated with [cooking fully] if there were to be any there. So not only are you going to kill the salmonella, you’ll have no risk of avian influenza.”
The new study on meat will only focus on dairy cows.
In experiments, scientists were able to infect young cows through their noses, but they believe the outbreak primarily seems to be moving among lactating dairy cows through shared milking equipment and human intervention, the USDA says.
It is not clear whether any beef cattle have been tested for H5N1.
“If you start testing and look for things, you may find them,” Kniel said. But in terms of food safety risks, she said: “I think we’re able to control it with certain behavioral changes and by the surveillance practices that are in place.”
The US Food and Drug Administration (FDA) also announced on Tuesday that continued tests have shown 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 across 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 did not have any traces of the virus, agency officials said – so they were not able to determine yet whether the ageing process inactivates the virus.
“In the case of the raw-milk cheese that we tested, none of the samples in the study had viral genomic material, suggesting that the herd producing the milk used to prepare the cheeses was from cows uninfected 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 ageing of cheeses made from unpasteurized milk is sufficient to inactivate the virus.”
There has been an uptick of interest in drinking unpasteurized milk, which can carry deadly pathogens and has no benefit over pasteurized milk, during this outbreak.
Officials continue to caution that drinking raw milk is dangerous. “Raw milk consumption does present a risk to consumers,” Grube said.
That was true long before the bird flu outbreak.
“It’s the one thing I always tell people: if there’s anything to avoid because of foodborne illness, it’s definitely raw milk,” said Kniel. Even cows that seem healthy could harbor pathogens deadly to humans. “The risk of consumption of raw milk and disease associated with campylobacter, cryptosporidium, E coli, listeria, salmonella – those are all really 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 clear yet whether consuming raw milk could cause H5N1 infection, but it seems to infect some mammals this way. Mice that were fed H5N1-infected milk quickly became ill, and several barn cats that fed on milk from infected cows have died.
“We don’t know what consumption of H5N1 in milk is going to do” among people, Kniel said.
