Weekend Round-Up: Bird Flu and Raw Milk

What you need to know about the ongoing H5N1 avian influenza outbreak

(Source)

Dear Readers,

You may have heard some news about an outbreak of bird flu on farms over the past few months and you probably have a lot of questions…

Why is it infecting cows?

Do I have anything to worry about??

Is milk safe to drink?!?

To be honest, I’ve held off writing about this topic since I never practiced as a large animal vet and I don’t have specific expertise in virology or public health. However, there is a lot of bad information going around online, so I figured it would be better to put out my take rather than let quackery have the last word. Wherever possible, I refer to actual experts in dairy medicine, epidemiology, infectious disease, and immunology to make sure I’m not contributing to the misinformation problem.

So for this (holiday) weekend round-up, let’s walk through what we know and don’t know about avian influenza spreading on farms across the US and how to stay healthy.

A Case of Zoonotic Spillover

Typically, avian influenza viruses stick to their avian hosts, causing havoc among birds and occasionally jumping to humans. Strains like H5N1 and H7N9 have preciously made headlines for their deadly outbreaks. Starting in March, the USDA, FDA and CDC reported finding high pathogenicity avian influenza (HPAI) in dairy cattle herds in Kansas and Texas. This is quite unusual as cows and birds have such different biologies that they aren't usually on each other's pathogen radar—in fact, this is the first case where HPAI has been detected in cows, and only the second time any type of bird flu has been found in ruminants (which include goats, sheep, and deer).

How did this happen? As with many infectious diseases, this is likely due to “zoonotic spillover,” when viruses jump from one species to another. This often happens in environments where different species are in close contact, such as mixed-species farms or markets. In this case, transmission from wild birds is the likely culprit.

Avian influenza viruses mutate rapidly. Occasionally, these mutations enable it to infect new hosts. In this case, a specific mutation seems to have allowed the virus to bind to receptors in bovine respiratory systems. The good news, per the AVMA:

“Initial testing by the USDA’s National Veterinary Services Laboratories (NVSL) has not found changes to the virus that would make it more transmissible to humans, which would indicate that the current risk to the public remains low.”

Updates from the Front Lines

For the latest news, I refer to the excellent Worms and Germs blog by Dr. Scott Weese, a large animal internal medicine and infectious disease specialist at the Ontario Veterinary College. This post provides an update on the newest developments in May. For starters, this version of H5N1 has likely been circulating longer than we thought:

“Genomic data suggest that the current H5N1 spillover into cattle likely occurred much earlier than was known. It was unlikely that we’d caught the first (or at least one of the first) affected dairy herds in March. Rather, it looks like the spillover into cattle in the US likely occurred in December 2023 (but maybe as early as October 2023). […] After that first bird-to-cow transmission, subsequent transmission is thought to have been from cow-to-cow, with spread on farms through contaminated milk, and spread between farms and states through movement of cattle. Given the limited evidence of virus in respiratory samples from cattle and the large viral load in milk, spread on farm is probably through human-associated milking practices, based on the high likelihood of tracking milk between cows during milking.”

What other animals have been infected so far?

“There has been subsequent spillover of this H5N1 strain from cattle into cats and poultry flocks. Some farm cats have had severe disease (and even died) from the virus; farm cats could possibly be good sentinels in this situation (i.e. if you see dead cats (more than usual) on the farm, consider looking for influenza in the cattle). Spillback into wild birds is also a concern, since if this strain goes back into wild birds, the situation becomes even harder to control: We can much more effectively monitor and control cow-to-cow transmission than an ongoing risk of exposure from wild birds (that also don’t respect political borders).”

There have been VERY rare cases of this H5N1 avian influenza detected in farm workers—only three people so far—but they have been mildly ill (the only symptom in one was conjunctivitis), and as stated before, the risk to the general public is considered very low. People who frequently interact with cows or wild birds should be more vigilant, and drinking raw milk is very risky, as I will discuss below.

(Source: CDC)

Is Milk in the Store Safe?

This outbreak of HPAI appears to be spreading through milk, and a number of news stories have breathlessly reported that the FDA found avian influenza viral fragments in milk from the grocery store. So it’s understandable that you might be worried about whether or not it’s safe to drink milk. The simple answer is:

YES!

How do we know? What the FDA found was dead, non-viable DNA fragments; they do NOT contain live virus particles that would be capable of infecting any people or animals. This is because all commercially sold milk is PASTEURIZED, not just to kill viruses, but also bacteria and parasites. Contrary to some conspiracy theories that have been spreading, pasteurization does NOT involve any chemicals, it is simply heat treatment, similar to boiling water when you’re camping.

For more details on this, listen to the immunologist

Dr. Andrea Love

:

“In this process [Pasteurization], the milk is rapidly heated to a specific temperature (usually around 161°F or 71.7°C) for a short period (usually 15 seconds), then rapidly cooled. This kills potentially harmful bacteria such as E. coli, Salmonella, and Listeria, as well as inactivates viruses such as influenza viruses, herpesviruses, parvoviruses, and others that may be found in dairy milk.

This rapid heating and cooling also preserves the taste of milk while limiting protein denaturation, thus also preserving the nutrition of milk.”

You can read her full article here:

Hey clickbait headlines: pasteurization kills H5N1 flu virus in milk

Raw Milk: Plenty of Risk, No Benefit

Ok, so milk in the grocery store is safe, but what about RAW milk?? Some alternative medicine types—and increasingly far-right conspiracy theorists like Infowars 🙄—are pushing the narrative that raw milk is safe and beneficial (Fact check: It is NOT).

Why is raw milk a concern? Even before this avian influenza outbreak, people were warned against drinking raw milk because it can harbor dangerous pathogens like E. coli, Salmonella, and Listeria. In fact, selling it is illegal or heavily restricted in dozens of states. From the New York Times:

“Public health officials have long warned Americans of the severe health risks that can come with drinking raw milk instead of pasteurized milk, which is heated to kill bacteria, viruses and other germs. Researchers at the Centers for Disease Control and Prevention found more than 200 disease outbreaks linked to unpasteurized milk from 1998 to 2018, leading to 2,645 illnesses, 228 hospitalizations and three deaths.”

Despite the risks, some people tout raw milk as having health benefits. Simply put, this is almost certainly untrue. In this post, the epidemiologist

Katelyn Jetelina

explains why immune protection from raw milk is likely impossible, and that rumors such as it being more nutritious or better for people with lactose intolerance have been largely discredited:

No, there are likely no immune benefits from raw milk

What Can You Do?

At this point, the answer is unfortunately…not much 🫤 The main things I would recommend:

• Stay informed. As the covid pandemic showed us, the facts on the ground in infectious disease outbreaks can change quickly. The following are some good sources for reliable and medically sound information to keep up with the latest news and public health recommendations:

  • American Veterinary Medical Association (AVMA) page on Avian Influenza

  • Centers for Disease Control and Prevention (CDC) page on H5N1 Outbreak

  • Worms and Germs Blog

• Use food safety best practices. Don’t drink unpasteurized milk. Encourage friends and family to understand the risks of raw milk. Wash your hands when handling uncooked meat and make sure to heat it to the appropriate temperate (particularly poultry).

• Avoid wild birds and sick livestock. Since H5N1 is circulating in wild birds in all 50 states, it would be smart to keep your distance from any wild birds, especially if they appear sick or are dead. Same goes for sick cows or poultry. Since some farm cats have gotten quite ill from H5N1, make sure to keep your pets away from those vectors as well.

As always, I will keep you up-to-date on major developments as I learn about them. I hope you all have a safe and relaxing holiday weekend!

—Eric