Samples of pasteurized milk tested positive for viral remnants of the bird flu virus, the Food and Drug Administration announced this week.
The agency said that pasteurization is likely to inactivate the virus, but the process could leave behind viral particles. Therefore, the findings do not represent the actual virus that may be a risk to consumers, the FDA said.
“To date, we have seen nothing that would change our assessment that the commercial milk supply is safe,” the agency said in an update. “Results from multiple studies will be made available in the next few days to weeks.”
The news comes as the FDA monitors an ongoing outbreak of bird flu among dairy herds across several states including Idaho, Kansas, Michigan, New Mexico, North Carolina, South Dakota and Texas. One person in Texas who worked on a commercial dairy farm recently tested positive for bird flu in just the second human case ever reported in the U.S.
Why Are Remnants of the Bird Flu Virus in Milk?
Bird flu typically infects wild birds, though it can spread to other animals. Wild migratory birds are believed to be the original source for the virus in cattle, though some evidence suggests the virus can spread between herds, according to the Department of Agriculture. There’s also evidence that the virus can spread from dairy cattle back into nearby poultry flocks.
Illness has been documented among older and younger, lactating cows. Officials have said that affected cows recover after supported care with “little to no associated mortality.”
The FDA stated that “only milk from healthy animals is authorized for distribution into interstate commerce for human consumption.”
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“Milk from ill (symptomatic) animals is being diverted or destroyed so that it does not enter the human food supply,” the agency said on its website last week. “Milk loss resulting from symptomatic cattle to date is too limited to have a major impact on supply and there should be no impact on the price of milk or other dairy products.”
During the course of the outbreak, the FDA has been evaluating milk from affected animals, including samples from the processing system and on the shelves in stores. It is unclear where the samples that tested positive for viral particles of bird flu originated.
Some have suggested the recent findings mean bird flu is more prevalent in dairy herds than previously thought.
Is Milk Safe From Bird Flu?
U.S. agencies this week said that the commercial milk supply is safe based on current information. The FDA and the Agriculture Department cited both the pasteurization process and the diversion or destruction of milk from sick cows for their assessment.
“The pasteurization process has served public health well for more than 100 years,” the FDA said. “Pasteurization is a process that kills harmful bacteria and viruses by heating milk to a specific temperature for a set period of time to make milk safer. Even if virus is detected in raw milk, pasteurization is generally expected to eliminate pathogens to a level that does not pose a risk to consumer health.”
It’s unclear if bird flu can be transmitted through the consumption of raw milk or raw cheese from an infected cow.
The FDA “recommends that industry does not manufacture or sell raw milk or raw milk cheese products made with milk from cows showing symptoms of illness, including those infected with avian influenza viruses or exposed to those infected with avian influenza viruses.”
What’s Being Done About It?
Federal officials announced Wednesday that lactating dairy cattle being moved between states will have to test negative for the bird flu virus in an effort to gather information and limit the spread of bird flu among cattle.
Additionally, any owners whose dairy cattle test positive prior to interstate movement will be required to provide information like animal movement tracing.
“The novel movement of H5N1 between wild birds and dairy cows requires further testing and time to develop a critical understanding to support any future courses of action,” the Agriculture Department said in a press release.
The agency added that “it is important to remember that thus far, we have not found changes to the virus that would make it more transmissible to humans and between people.”