Is H5N1’s Jump to Cattle a Big Deal?

I’m sure you’ve heard that the H5N1 avian influenza strain has been recently discovered to have jumped to cattle and has been detected (by PCR) in raw milk in 9 states. What are the public health implications and what’s being done to investigate and intervene?

Background

Let’s start with a quick history of how the H5N1 avian influenza virus got started.

In 2020 it appears that there was some reassortment (aka gene-swapping) between dually infected domestic poultry and wild bird influenza viruses that resulted in the new ‘HPAI’ H5N1 influenza virus.

In February 2022 the USDA discovered this new version of the influenza virus rifled through a US commercial turkey facility, marking the first known commercial outbreak of the virus in the US.

The H5N1 avian virus is shed in the saliva, mucous, and feces of infected birds. It spreads rapidly through poultry flocks and among wild birds and is quite lethal for poultry.  An estimated half a billion farmed birds have been slaughtered in efforts to contain the virus.

For the most part the virus has just been making birds sick – but there have been detections of the virus in all kinds of mammals as well – ranging from sea lions to mink to polar bears.

New Regulations after Some Cattle Became Infected

Last month, the USDA found that the virus had begun to infect domestic cattle…  although the symptoms and virulence in cattle is much lower than in birds. While infected cattle had some symptoms, they haven’t been serious nor lethal (in contrast with the effect of the virus on birds).

The USDA is the regulatory authority for the testing, investigation, and control measures for both the birds and the cattle. USDA has several new regulatory measures already in place that you can see here: aphis-requirements-recommendations-hpai-livestock.pdf (usda.gov). 

Virus Surveillance & Investigations

So far all of USDA’s testing in actual meat from cattle is clear of the virus, but it’s showing up in high concentrations in the milk of infected dairy cows.

The vast majority of milk on the shelf is pasteurized and not a threat at all because if the virus is in the milk, the heat of pasteurization kills it. Raw milk (legal in Arizona) of course is a theoretical risk for humans but is unlikely to cause severe illness unless the virus changes dramatically from where it is today.

Workers close to infected cows and birds haven’t been becoming sick – except for one case of pink eye where a guy got infected milk while he was working the cows.

The meat that has been tested at retail sites in the 9 states that have found infected dairy cows has so far all been negative. USDA is testing meat at licensed slaughterhouses (using PCR), but the results aren’t out yet.

A hamburger study is underway at the slaughterhouses too. No results yet – but there will likely be results by next week.

Here are the results so far: Updates on H5N1 Beef Safety Studies | Animal and Plant Health Inspection Service 

USDA still doesn’t know exactly how the cows are getting it from the birds – but that’s under investigation. My bet is that it’s because some farmers feed dairy cattle chicken feces (they call it litter), which could be infecting the cows.

Bird flu outbreak: Arizona farms haven’t detected any cases

If that turns out to be the case the intervention is simple – order farmers to stop feeding chicken feces to cows. Whether they’d comply is another matter.

Future Implications

As for the H5N1 virus mutating in cows and jumping to people in a much more virulent form…  yeah it’s theoretically possible but has never been observed before.

The normal pathway for new virulent influenza virus (pandemics) is birds > pigs > humans. That’s the long-term pattern including H1N1 back in 2009. Why? Because believe it or not pigs are close to humans on the biological tree and have similar respiratory receptors.

New strains almost always come from China because in rural China humans, pigs and birds (usually geese) all live together.  Cattle are far from humans on the mammal tree so it’s unlikely the H5N1 virus would mutate and become a virulent human strain in a bovine.