There’s a reason we pasteurize milk: there’s always a risk of contamination of raw milk with infectious agents, and pasteurization is a cheap, easy and effective way to mitigate disease risks from drinking milk and other dairy products. There are no clear benefits to raw milk (despite what some may say) and the risks from drinking raw milk are clear (and have been known for decades).

However, raw (unpasteurized) milk can still be legally sold in some states in the US (it is not allowed in Ontario). It’s getting more attention as a certain high-profile US politician talks about raw milk alongside his anti-[lots of things] agenda. That’s a huge concern for human health. There are some animal health issues too, and since that’s my turf, I’ll talk about those.

A recent report from LA County highlights the risk of H5N1 influenza in raw milk from infected cows in California (where hundreds of herd have been affected since the summer). So far, this seems to just be a problem in the US, as they are the only country where H5N1 flu has spread to (and between) dairy cattle. Lack of an aggressive initial response, in combination with how dairy cattle are managed and moved across the US, led to widespread infections on dairy farms in certain states. The strain of H5N1 flu affected the cattle has a unique predilection for the bovine udder. Infected cattle shed huge amounts of virus in their milk, and milk (and milking equipment) therefore seems to be the main source of transmission from and between cattle.

Milk from infected cattle shouldn’t enter the food chain, but not all infected cattle are identified right away. Pasteurization will effectively inactive influenza virus, so pasteurized milk is safe regardless. The concern is with consumption raw milk (whether it is sold legally or illegally, depending on the jurisdiction).

The LA County Department of Public Health has reported the deaths of two cats from H5 influenza (that will almost certainly be confirmed as H5N1 when all the testing is completed). Both cats had consumed recalled (contaminated) raw milk, and had what seems to be a typical disease course for cats with this virus. They had some initial non-specific signs (e.g. loss of appetite, fever) then developed severe, progressive and ultimately fatal neurological disease. Presumably public health is closely monitoring the people and other animals in the household.

They are also investigating three other feline cases from a different household. One initially tested positive for influenza already, so it’s pretty safe to assume this is another H5N1 cluster. Two cats in that household died “after worsening respiratory illness.” More details about that would be nice since we still don’t have a good handle on the scope of disease that occurs in cats and dogs, but it would help us to better flag potential flu cases. There’s no known link to raw milk for these three cats yet, but they are investigating potential sources of exposure, including raw milk.

Almost certainly they are trying to sequence the virus from these cases.

• They’ll presumably find the dairy-associated strain of H5N1 in the first household; that would make a solid link to the raw milk as the source.
• Sequencing from the other household will be important to help sort out potential sources (e.g. dairy strain vs strains in wild birds in the area).

While avoiding raw milk doesn’t eliminate all H5N1 flu risks (since infected birds are still a source), it’s a completely avoidable risk factor. There are no health benefits from raw milk, but there are very clear risks (which now include influenza as well). The cost:benefit calculus is pretty straightforward here.

What about risks from raw milk in areas outside the US where there’s no known H5N1 flu in dairy cattle?

There are still other infectious disease risks from raw milk. Also, just because we don’t know that there are cases now doesn’t mean that there are actually none or that there will be none forever.

It’s pretty simple to me: just avoid drinking raw milk (and other unpasteurized dairy products), but remember that pasteurized milk and dairy products are safe!