New studies show that pasteurization inactivates H5N1 bird flu in milk

EExtensive testing of pasteurized, commercially purchased milk and other dairy products from 38 states found no evidence of a live H5N1 bird flu virus, Food and Drug Administration officials said at a news conference Wednesday.

The results confirmed the findings of earlier testing of a more limited number of samples and add weight to the FDA’s conclusion that pasteurized milk products are safe for consumption despite a widespread outbreak of cows infected with H5N1.

“These additional, preliminary results further confirm the safety of the U.S. commercial milk supply,” Donald Prater, acting director of the FDA’s Center of Food Safety and Applied Nutrition, told reporters.

Last week, the FDA announced that it had conducted PCR tests on 96 commercially purchased dairy products and found genetic traces of the H5N1 virus in 1 in 5 samples, but initial data showed there was no live virus. On Wednesday, the agency reported the results of testing another 201 products, including cottage cheese and sour cream, in addition to milk. All PCR-positive samples were then injected into embryonated chicken eggs to see if active virus could be grown – the gold standard test for assessing the viability of a flu virus. None of the samples produced viable, replicating virus, Prater said.

The 297 samples the FDA has tested so far represent dairy products from 38 states. In addition, several samples of commercially available powdered infant formula and other milk powder products were tested. All PCR results for these products were negative. The agency has not disclosed when it plans to make its full analysis, including which products were purchased in which states, available to the public.

In support of the FDA data, academic researchers from Ohio State University and St. Jude Children’s Research Hospital told STAT Tuesday evening that their own study of 58 PCR-positive milk samples taken from Texas, Kansas and eight other Midwestern states also failed to provide any evidence that H5N1 can survive the pasteurization process.

“It was about what we expected,” said Richard Webby, an influenza virologist at St. Jude whose lab conducted the viral growth experiments — both in mammalian cell lines and in embryonated chicken eggs. The samples they tested had varying levels of viral RNA, from very low to quite high amounts, Webby said. Although it looked nothing like what came out of the udders of infected cows. “Certainly the viral load is being diluted,” he said.

But there was still enough RNA in the samples they tested that if those levels represented a real, viable virus, he expected to find it.

“If these samples had entire virus particles that could replicate, we would have expected growth in cells and eggs, which we did not see. The bottom line is that we simply don’t think there is a replicating virus in these samples. What we find is probably just remnants of the virus.”

Webby and other scientists are more concerned about the potential health risks of drinking raw milk. Although little is currently known about the possibility of humans contracting H5N1 from consuming raw milk from infected cows, researchers are sounding the alarm that the consequences could be serious. In the wild, mammals such as foxes, bears and seals that have become ill with H5N1 – believed to be from eating infected birds or drinking water contaminated with their feces – have had severe symptoms, including brain damage and death.

“In humans, we don’t know how much milk you would have to drink to become infected, and if 10 people drank raw milk from an infected cow, how many would be affected,” Webby said. “But it’s not an experiment I would want to participate in.”

The FDA urges consumers not to drink raw milk or eat raw milk cheeses. That’s a position the agency has long held because of the other health risks these products pose, but it’s not has emphasized it again in the context of the current outbreak. “We continue to strongly advise against the consumption of raw milk,” Prater said at the press conference on Wednesday.

He did not say whether the FDA has conducted tests on raw milk products currently on the market. But it does test samples of pooled raw milk – milk brought from multiple farms to centralized processing facilities where pasteurization takes place. This will be used to better understand how much virus from asymptomatic or presymptomatic animals enters milk production, and to inform further studies to validate the effectiveness of different pasteurization methods, Prater said.

The FDA has also recommended that the dairy industry “not produce or sell raw milk or raw milk products, including raw milk cheese, made with milk from cows showing symptoms of disease, including cows infected with bird flu viruses or exposed to cows infected with bird flu viruses. .” It also has the producers called out to discard milk from affected cows and to pasteurize raw milk from exposed cattle before feeding it to other animals.

Cats fed raw milk from cows infected with H5N1 have become ill and some have died, a study has found. study published Monday. So far, only one person – a farm worker in Texas who developed conjunctivitis – has been confirmed to have been infected by dairy cows.

H5N1 bird flu has been circulating among dairy cow herds in parts of the country for months. So far, the U.S. Department of Agriculture has reported that 36 herds in nine states have tested positive for the virus, but genetic evidence of H5N1 in milk suggests the outbreak is more widespread.