Bird flu continues to pose a real threat to public health, but at least apparently not to our food supply. The Food and Drug Administration and the U.S. Department of Agriculture separately announced late Wednesday that their tests of pasteurized milk and ground beef found no live H5N1 in samples that were at risk of contamination. The results appear to confirm that pasteurization can effectively neutralize the virus if it enters milk, but consuming contaminated raw milk could still be dangerous.
Dozens of dairy farms in nine states have recently experienced outbreaks of the highly pathogenic H5N1 virus in cows, with cases dating back to late 2023. These strains are considered highly pathogenic to native birds due to the massive illness and mortality they can cause in wild and wild animals. So far, infected cows have generally avoided serious illness, but many have experienced symptoms such as reduced or discolored milk production and loss of appetite. There have also been several fatal cases of H5N1 in cats associated with these farm outbreaks, along with at least one non-fatal human case.
At the end of April, the FDA reported that it had discovered genetic material from H5N1 strains in samples of store-bought pasteurized milk, results that were later repeated by other researchers. Officials noted at the time that the method used to detect H5N1 in milk – a highly sensitive quantitative polymerase chain reaction (qPCR) test – could not confirm the presence of live virus. And the FDA said it would then conduct “gold standard” testing, which could include attempting to inoculate (culture) samples of the virus detected by qPCR in chicken eggs.
Last Friday, the FDA announced that no live virus was found in a first round of egg vaccine tests; Yesterday it was reported that a larger round of tests also came back negative. In total, the agency tested nearly 300 samples of dairy products, including sour cream and cottage cheese, collected in 38 states.
“[T]“These results confirm our assessment that the commercial milk supply is safe,” the FDA said said in its latest update.
Elsewhere a USDA report The meat supply assessment study published on Wednesday was intended to reassure the public. Officials collected 30 samples of ground beef from stores in states where there had been dairy farm outbreaks and sent them to the National Veterinary Services Laboratories for PCR testing. All of these tests came back negative. Additionally, PCR tests of retail powdered infant formula and powdered milk products marketed as infant formula by the FDA were also negative.
Experts assumed that pasteurization would render H5N1, like many other infectious germs, inert. So the results aren’t all that surprising. But given the unprecedented spread of avian flu in dairy cows, it was still important to know for sure. And we’re not out of the woods yet. The mere discovery of H5N1 in store-bought milk, coupled with genetic evidence that it appeared in cows months before anyone knew it, strongly suggests that these outbreaks are far larger than our current data shows.
Bird flu always poses a potentially serious threat, in part because the flu strains found in birds are less familiar to the immune systems of humans and other mammals. Currently, these viruses do not transmit well between people. But the longer H5N1 can remain in cows, the greater the likelihood that some strains will be able to adapt and spread better among mammals, including humans. And the right selection of mutations could turn a bird flu virus into a deadly and fast-spreading pandemic germ.
While pasteurized milk is safe to drink, the same is not necessarily true for raw milk. is raw milk regularly a vector for many infectious diseases. And there are some cases of H5N1 in cats already suspected This could be due to the cats drinking contaminated raw milk. The FDA announced Wednesday that it will next expand its testing to raw milk to better assess the threat posed by these products.