One more reason not to drink raw milk: H5N1 bird flu

The H5N1 bird flu virus has been officially confirmed in a sample of raw milk sold at stores in California. No one has reported illness associated with consumption of raw milk to date, but the concern of further spread of this virus as it makes its way through dairy cattle, and now dairy products, is concerning.

H5N1 virus found in raw milk purchased at stores:

On November 24, 2024, the California Department of Public Health issued a notice advising of a voluntary recall of raw milk sold in stores. The reason for the recall? The milk was positive H5N1, also known as bird flu.  

As noted in the recall notice, the milk’s expiration date was listed as 11/27/2024. So it had been on the shelves for a little while before it was discovered it was contaminated with bird flu.

Importantly, there have not been any reports of illness in people associated with purchasing this milk. So it wasn’t because someone got sick that the milk was tested. The local public health authority, the Public Health Laboratory of Santa Clara County had been conducting routine testing of raw milk supplied to retail stores. This routine testing of raw milk available for purchase was conducted “as a second line of consumer protection.”

 

 

Testing identified the bird flu virus “in one sample of raw milk purchased at a retail outlet.” The positive result was confirmed by the state’s animal and food safety laboratory. A voluntary recall was issued by the raw milk producer, Raw Farm, LLC, located in Fresno County. Stores with this product on their shelves were advised to remove it and customers who purchased the milk were advised to return any “remaining product” to the store where it was purchased.

 

But how did milk containing bird flu make its way into the stores?

Ever since H5N1 was first found in dairy cows in early Spring, there has been growing concern about the safety of the milk supply. To that end, the USDA and its state and local partners in the industry have taken some steps to prevent contaminated milk from entering the supply. This included separation of clinically ill cattle and collection and disposal of milk from sick cows. The USDA also required that all dairy cattle test negative for the virus prior to interstate transport. Some states like Colorado and, more recently, Pennsylvania, started requiring bulk milk tank testing, but this is not uniform even in states with confirmed H5N1 cattle infections.

Increased testing in cattle herds was encouraged as the outbreaks continued, but was not made mandatory. Moreover, the focus of testing is when dairy cattle are showing signs of illness, but the way the virus has transmitted so fast and through so many cattle herds has some studies suggesting asymptomatic spread.

There was also some interesting pushback from the dairy and agricultural private sectors. For example, in early April the American Association of Bovine Practitioners (AABP) issued an open letter, where the group argued that the disease not be referred to as bird flu or H5N1, but as “bovine influenza A.” This rebranding effort was not adopted by the scientific community. Additionally, as the outbreaks progressed, anecdotal reports surfaced about veterinarians facing pressure from farms they held contracts with not to test for the virus and were discouraged from even suggesting it.

So it is perhaps not surprising that, despite the protocols put in place, we have now seen H5N1 positive raw milk available for purchase and, presumably, consumption. For those who have been following these outbreaks, we have already seen something similar happen with commercially available pasteurized milk.

H5N1 found in gallons of pasteurized milk in grocery stores:

In April 2024, samples of pasteurized milk obtained from grocery stores tested positive for H5N1. Dr. Andrew Bowman, an Ohio State veterinary epidemiologist took a road trip to different retail stores in the Midwest and purchased 150 gallons of milk to test for bird flu. Given the incredibly high amounts of virus present in milk from sick cows, Dr. Bowman thought there was a risk that some virus was getting into the milk supply. The study of commercial milk samples found that 38% of retail milk samples tested positive. Additionally, the FDA conducted its own testing of retail milk samples, finding that 1 in 5 retail samples returning a positive result.

The results of these studies were concerning, given the amount of milk available for consumer purchase in the grocery stores. Even more alarming was that the results clearly showed that the H5N1 virus was more widespread than what was officially reported. As stated by the well-known influenza virologist Richard Webby:

“The fact that you can go into a supermarket and 30% to 40% of those samples test positive, that suggests there’s more of the virus around than is currently being recognized.”

The FDA maintained that “pasteurization is generally expected to eliminate pathogens to a level that does not pose a risk to consumer health.” Moreover, it was not clear if the positive results were because there was live virus or viral fragments in the milk. PCR testing can show a positive result where there is infectious virus or viral RNA, i.e., remnants of viral genetic code that, while not infectious, points to a prior infection. Laboratory studies geared towards mimicking the conditions of pasteurization indicate that the process does render the virus unable to cause infection. Additionally, when laboratory scientists tried to grow the H5N1 virus directly from these positive milk samples in the lab (what the FDA called “egg inoculation tests”) they were unable to do so, indicating no live virus. So it is safe to say that pasteurized milk won’t give you the bird flu.

But what about raw milk with H5N1 virus?

We now have at least one instance where raw milk contaminated with H5N1 made its way into stores and some of it was purchased for human consumption. This is despite protocols being in place to prevent that from happening, such as the requirement that milk from dairy cattle sick with H5N1 be disposed of and not put into the food supply.

Was this milk from an asymptomatic cow? Was it milk from multiple cows mixed together? Was it milk from a cow that previously had the virus but was thought to have cleared the infection? I hope we get answers to these questions. But perhaps the most important one is what is the risk of being infected with bird flu if someone makes the decision, however ill advised, to drink raw milk?

From a growing number of scientific studies, we know that this H5N1 strain infecting dairy cattle replicates to very high levels in the mammary glands of lactating cows. The massive amount of virus in the udder of lactating cattle greatly effects the milk. Indeed, perhaps the most noticeable symptom in dairy cows is a sudden decrease or drop in milk production. Milk collected from sick cows is described as thick or yellowish. As far as I know, no one has been drinking this milk (nor would they want to if you’ve seen the pictures).

What we need to know is if the positive results from the milk samples were due to live virus or viral RNA fragments. This requires laboratory testing, like with the pasteurized milk samples, to see if the virus can be grown in the lab.

 

 

Call it a hunch, but given the incredibly high levels of infectious virus found in the milk of sick dairy cows, I think there is a better chance of at least some infectious virus being found in raw milk samples.

So if there is infectious H5N1 virus in raw milk available for consumption, what are the risks associated with drinking that milk? Right now, at least according to the news articles, experts apparently aren’t sure of the health implications. For example, STAT news wrote an article on this, with the sub-headline: “Health implications of drinking H5N1-laced milk are unknown, but scientists express concern”. I’ll bet they do.

The health implications are “unknown” because no one has experimented with giving contaminated raw milk to human test subjects. That’s what they use mice and ferrets for. One expert quoted in this article, Michael Osterholm, is a very well-known expert in epidemiology and influenza. On the issue of risk of infection from drinking raw milk containing H5N1, he told STAT news:

“We don’t know what oral consumption of milk will do. Some people have extrapolated from the fact that . . . cats have [become infected] from oral ingestion of milk. We don’t know how that plays in humans . . . It’s not a good thing. We surely don’t want to have it happen. But we also have to acknowledge that we don’t know exactly what the risk is.”

 We may not have official data on what happens when a human ingests raw milk that has H5N1 in it, but can’t we just assume that raw milk containing bird flu is a bad thing for us? It seems rather obvious.

 

 

Moreover, we already know raw milk from infected cows can cause bird flu infections in humans. Most (if not all) of the human H5N1 cases in dairy farm workers had a connection to raw milk from infected cattle, typically through activities in the milking parlor. The cases have been mild (by bird flu standards) but characterized by conjunctivitis, indicating eye exposure to raw milk positive with the virus. 

So if a human can catch bird flu from raw milk splashing them in the eye, or by milk getting on their hands and then touching their eye, why wouldn’t they be able to catch it from drinking that same H5N1 positive milk?

As someone who listens to Dr. Osterholm’s podcast Osterholm Update, I recall him stating multiple times that people shouldn’t drink raw milk, especially now. I am going to go out on a limb here and say that, in addition to the well-known reasons to avoid raw milk, bird flu is now a big one. You do not want to drink milk that has infectious H5N1 virus in it.

 

Just ask the farm cats. . .

 

 

. . . like the ones Dr. Osterholm mentioned above. When the cattle outbreaks were first reported in early March, there were also reports of cats on some dairy farms dying.

According to a CDC study published in July, in at least one Texas dairy farm, “deaths occurred in domestic cats fed raw colostrum and milk from sick cows that were in the hospital parlor.” On this farm resided 24 farm cats, all of which had “been fed with milk from sick cows.” The day after the cows started showing symptoms, the cats also showed symptoms, although were the cats it was much worse. The sick cats showed “depressed mental state, stiff body movements, ataxia, blindness, circling, and copious oculonasal discharge.” A few days after the illness was first noted, “several cats died in a cluster.” In total, about 50% of these farm cats died. The laboratory study examined tissue samples from 2 of the deceased cats, noting signs of “systemic viral infection.” These signs included brain hemorrhages, encephalitis, pneumonia, myocarditis, with H5N1 virus being found in the brain, lung, heart, and eyes.

So it did not go well for the cats who drank H5N1 positive raw milk. Obviously, it is unclear how much of this would be similar in humans. The amount of infectious virus in raw milk from sick cows is incredibly high, and maybe that viral load is lessened somehow in commercially available raw milk. Maybe people that drink raw milk have been lucky and don’t typically drink milk produced from the 650+ farms infected with bird flu. Or maybe the lack of human cases from drinking raw milk is related to receptor binding. Our upper respiratory tract has the a-6 receptors, which human flu binds to, while our eyes contain avian-style a-3 receptors, which bird flu binds to. So all these cases of conjunctivitis make sense in that regard. Avian flu viruses have a harder time binding to a-6 receptors, which is why H5N1 has never gained sustained human-to-human transmission. I just would not bet on that as a fail safe in drinking raw milk, because viruses evolve all the time, and the more opportunities a virus, like H5N1, has to infect humans, the more it can adapt to humans.

For now, we await the results of the science.

Until next time.