A recent opinion article in the Washington Post about how to protect cats from H5N1 influenza includes some good considerations, but alongside some bad information. It’s prompted me to write a bit about pet food preparation and how it does (and does not) affect the presence of infectious pathogens (but please keep in mind while reading this that I’m an infectious disease veterinarian and not a food safety specialist!).

In the article, there’s a statement from a professor at a school of public health who said they were avoiding canned pet food “…largely because the pet food industry is not as closely regulated as the human food industry,” …Coleman has not been giving her cats canned food, as it might contain unpasteurized milk. Kibble, on the other hand, is heated at very high temperatures, which, like pasteurization, would kill H5N1.”

However, canned pet food is actually likely the lowest-risk form of pet food when it comes to pathogens. Processing conditions are very different for different forms of pet food, and the processing significantly impacts pathogen survival:

Canned pet food

These diets are heated to high temperatures (235F/115C or above), akin to sterilization. If it wasn’t, cans would spoil quickly and often explode because canned food is otherwise a great culture medium for bacteria. Canning will absolutely kill H5N1, full stop. No question, no concerns. Move on please.

Kibble / dry pet food

These diets are also thoroughly cooked prior to being made into kibble. The temperatures used are not standardized, but are well above the recommended temperature for cooking poultry (165F/74C). Heat is also generated during extrusion process (forming the food into kibble) and desiccation (being dry food) will also decrease pathogen survival. The food isn’t sterile, but as long as the finished product is kept away from raw ingredients (a pretty standard food safety step), I have no concerns about flu contamination in dry kibble.

Lightly or gently cooked diets

These diets are in the grey zone. They’re marketed as diets that are cooked but are not to the same extent as kibble. Killing pathogens in food is a function of temperature and time. If they reach the recommended cooking temperature for poultry (165F/74C), any flu virus in the product should be long gone. At lower temperatures, there’s more variability and more need for a longer cooking time (e.g. 60C/140F for 30 minutes). A challenge with these diets is the lack of information about the “gentle” cooking parameters (temperature and time). I suspect they likely all hit a high enough temperature to at least kill flu viruses (which are easier to kill than some food borne bacteria) but that’s a bit of a guess. I’d consider them low risk overall, but if I was going to feed a diet like this I’d ask the company how they cook the food, to be sure.

High pressure pasteurized raw diets

High pressure pasteurization (HPP) uses pressure (instead of heat) to inactivate microorganisms. However, the effectiveness is dependent on the amount of pressure and how long it’s maintained, as well as the food matrix itself, and volume of food undergoing HPP. If the method is validated and performed properly, the risk of flu virus surviving the process should be really low. However, we’ve seen at least one report of fatal H5N1 influenza in a cat that was eating a HPP-treated diet. Recalls of HPP treated diets for Salmonella contamination are also far from rare (and if the process doesn’t kill Salmonella in a certain product, we’d be concerned it might not effectively kill flu virus either). I consider HPP a risk reduction method, not a risk elimination method. If a company can show that their method kills flu (or a proxy virus), then I’d be more confident the diet is safe (at least from a flu standpoint). 

Raw diets with “natural preservatives”

Preservatives are used to reduce spoilage. That means they reduce growth of bacteria that are already in the food. They are not designed to kill pathogens (bacteria or viruses) in the food. So, whether or not there are preservatives (and whether or not they are considered “natural”) likely has no impact on survival of and risk of contamination with H5N1 flu in the diet.

Freeze-dried pet food

These diets are frozen, and then the water is removed under vacuum. Freeze drying is actually great method for preserving viruses for long-term storage in laboratories. I’m not aware of any evidence of any impact of freeze drying on survival of flu viruses, so until then I would assume that freeze dried diets are the same risk as fresh diets.

Raw (fresh) poultry

If H5N1 flu is present in a bird, it will be present in the meat from that bird. If there are no steps to kill it, flu virus can persist for a while in that nice moist environment, even after the bird has been slaughtered or died. Refrigeration probably helps with survival of the virus. Freezing probably has a bit of impact, since freeze-thaw cycles can impact viral viability, but I have no confidence in simply freezing the meat to significantly reduce viral contamination, and would not consider frozen raw diets to be any different than fresh in terms of risk. Untreated raw poultry is undoubtedly the highest risk pet food when it comes to H5N1 flu (not to mention a lot of other pathogens as well).