Just How Infectious Is The Bird Flu In Cows’ Milk Anyway?

There’s a rather bleak joke that goes:

Doctor: “I’m afraid I have bad news for you; your condition is now terminal”
Patient: “How long do I have?”
Doctor: “Ten…”
Patient: “Ten what? Years? Months?”
Doctor: “Nine…”

Sometimes, of course, humor itself can help extend life, by the way: Laugh Often, To Laugh Longest!

In this case, the situation isn’t quite as bad as in the joke, but the answer to the question today is also:

Ten

That’s the number of viral particles it takes for infection to occur.

Which means that any strategy for stopping transmission has to be truly near-perfect, so as to not let that many (10) viral particles through.

Researchers (Dr. Carolyn Lee et al.) found that as few as 10 H5N1 viral particles getting into a cow’s mammary gland can establish a productive infection, leading to high levels of virus shedding in milk consumed by humans.

This helps explain how bird bird flu spread so well through US dairy farms despite control efforts, because only a very small quantity of the virus is needed to infect a cow under the right circumstances. Nevertheless, it was very surprising when first taking hold, as the virus appears to preferentially infect the mammary gland rather than the respiratory tract, unlike typical influenza infections.

To quote a corresponding author on the study,

❝This work has all been done in response to the unprecedented spillover of avian influenza into dairy cattle. Initially, we had no idea that cows could even be infected with influenza, let alone that the mammary gland was involved. That in and of itself was a major paradigm shift: It’s not respiratory.

There is still the bigger question of spillover from wild birds into cows. In waterfowl, it’s a pathogen replicating in their gut. How in the world does it go from a duck’s intestine into a cow’s mammary gland? That’s a head scratcher.❞

~ Dr. Andrew Bowman, corresponding author

 Infected cows produced milk with very high viral concentrations for more than a week, and even the lowest infectious dose tested resulted in substantial viral shedding into milk.

You may be wondering why everyone isn’t getting sick (apart from those who don’t consume dairy), and the answer is that pasteurization inactivates the virus.

We wrote about that, here: Pasteurization: What It Does And Doesn’t Do

So with that in mind, it’s one more reason Why you shouldn’t drink raw milk!

You can read the paper itself in full, here: Dairy cows infected with influenza A(H5N1) reveals low infectious dose and transmission barriers

Want to learn more?

To get a lot deeper into the topic of avoiding the toxins the industrial world (including, but not limited to, the animal agriculture industry) likes to throw at us, you might like this book we reviewed:

Healthy Living in a Contaminated World – by Dr. Donald Hoernschemeyer

Take care!