The United States will track bird flu infections in dairy cows brought to slaughter to understand how the virus infects meat and will also continue to test raw milk cheeses to see if the virus is inactivated during the aging process.
The renewed focus on the U.S. food supply is the latest front in efforts to combat the infectious avian flu virus, or H5N1, that has set off alarm bells around the world about a potential future pandemic.
Regulators will inspect 800 samples of dairy cows at slaughterhouses. Dairy cows are typically slaughtered when they no longer produce milk or when they retire. They account for about 10% of U.S. beef production, usually in the form of ground beef.
The new livestock survey, due to start in mid-September, will be nationally representative and will give a clearer picture of the spread of the virus in dairy cow meat. It could also provide insight into potential risks.
If a sample is positive, the U.S. Department of Agriculture (USDA) will purchase the carcass for further testing. These studies could include determining whether the virus is viable (if it can replicate in the lab) and at what temperature it is killed.
An earlier study in May analyzed 109 muscle samples from cows that showed signs of illness after slaughter and found H5N1 particles in one dairy cow. The animal was not distributed to stores. Another study analyzed samples of ground beef available in stores; none of the meat tested positive.
In another study, scientists injected ground beef with a mimic virus and then cooked the meat. Weighing 10 ounces, the burgers were thicker than what consumers might find at a fast-food restaurant, making them “very thick for the worst-case scenario,” said José Emilio Esteban, the USDA’s undersecretary for food safety.
But cooking them completely inactivated the virus, he added.
At medium (140°F) and well done (160°F), the virus was not detected. These internal temperatures have long been recommended by the USDA Food Safety and Inspection Service.
“If you cook it under those conditions, it should be completely safe to eat,” Esteban said.
At 120°F/49°C, or a rare level, the copycat virus was “significantly inactivated” in burgers with high levels of added virus, the USDA report said.
According to Kali Kniel, a professor of microbial food safety at the University of Delaware, cooking meat thoroughly helps eradicate all sorts of foodborne pathogens. “Consumers need to be aware of the risk of disease transmission and the control they have in their own kitchen,” she added.
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.”
Ground beef is typically made from multiple cows, increasing the risk of foodborne illness when it’s not fully cooked, she said.
“We know that hamburgers are always riskier for these pathogens,” Kniel said. But “any viral particles would be inactivated by (thorough cooking) if they were there. So not only are you going to kill the salmonella, you’re not going to have any risk of avian flu.”
The new meat study will focus only on dairy cows.
In experiments, scientists have been able to infect young cows through the nose, but they believe the outbreak appears to be spreading primarily among lactating dairy cows through shared milking equipment and human intervention, the USDA says.
It is not known whether beef cattle have been tested for the H5N1 virus.
“If you start testing and looking for things, you might find them,” Kniel said. But when it comes to food safety risks, she said, “I think we’re able to control them with some behavioral changes and monitoring practices that we have in place.”
The U.S. Food and Drug Administration (FDA) also announced Tuesday that ongoing testing has shown that pasteurization completely inactivates the bird flu virus in milk, making pasteurized milk safe to drink.
In June and July, they examined 167 dairy products, including raw-milk butter and cheese, available in stores in 27 states. About 17% of the products contained inactivated virus particles, but none of them were viable, officials said.
Hard cheeses made from raw milk and aged for at least 60 days showed no traces of the virus, agency officials said. So they have not yet been able to determine whether the aging process inactivates the virus.
“In the case of the raw milk cheese we tested, none of the samples in the study contained viral genomic material, suggesting that the herd producing the milk used to make the cheeses came from cows that were uninfected at the time of milking,” said Steve Grube, chief medical officer of 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.”
Since the outbreak, there has been a renewed interest in consuming unpasteurized milk, which can contain deadly pathogens and has no advantage over pasteurized milk.
Authorities continue to warn about the dangers of consuming raw milk. “Consuming raw milk poses a risk to consumers,” Grube said.
This was true long before the bird flu epidemic.
“That’s the one thing I always tell people: If there’s one thing to avoid because of 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 illnesses associated with campylobacter, cryptosporidium, E. coli, listeria, salmonella — those are all very high risks.”
One E. coli cell producing Shiga toxin can kill a person, and 100 salmonella cells can make someone sick for the rest of their life, she said.
It is not yet known whether drinking raw milk can cause H5N1 infection, but it appears that the virus infects some mammals in this way. Mice fed H5N1-infected milk have rapidly become ill, and several farm cats that drank milk from infected cows have died.
“We don’t know what effect consuming H5N1 in milk is going to have” on the population, Kniel said.
