More than a dozen domestic house cats have been sickened or killed after eating raw cat food tainted with the bird flu virus. The Food and Drug Administration (FDA) says it is now prompting a federal probe into how the virus got into the pet food supply chain.

“The FDA is aware of reports of death or illness associated with uncooked food in 13 domestic cats in eight households, one exotic cat in one household, and an unknown number of animals at two sanctuaries for large felids,” an FDA official said in a statement.

The FDA has now tasked investigators with backtracing the outbreaks, the official said. Testing is underway, but it could take several weeks to yield results to pin down the source. That is if the source can even be found.

It is still unclear how the virus spread into pet food, according to health officials. Taxpayers have funded record numbers of poultry being culled in an effort to stem bird flu outbreaks, and U.S. officials said this month that farmers are not allowed to use meat from those birds in pet food. It is quite likely that more birds have died from culling than from getting avian influenza.

Rulers Culling Birds Amid Avian Influenza

“Affected flocks that are depopulated as part of USDA’s efforts to control H5N1 are not permitted in any food product at all. They are most frequently composted on site, as part of the efforts to mitigate the spread of the virus,” Eric Deeble, Deputy Under Secretary for Marketing and Regulatory Programs at the U.S. Department of Agriculture, told reporters last week, according to a report by CBS News. 

Raw and minimally processed pet foods make up a minority of pet food sales in the United States, but the consulting firm OC&C said last year that there’s been “rapid growth” in the market. It’s likely due to the understanding that processed foods are not healthy for human consumption, so they probably are also detrimental when our pets consume them. Cats are obligate carnivores, which means they must have meat in their diet. Depriving a cat of its proper nutrition is abuse at best. There is no plant material that can substitute for a cat’s nutritional requirements.