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An emerging trend among pet owners is the practice of feeding dogs and cats raw meat. This idea is that we should put our domestic cats and dogs on diets that more closely approximate what they might eat in nature. New research from Europe shows the surprising degree to which germs and parasites can be found in commercial raw-meat products—posing potential health risks to both pets and their owners.

An article in the Washington Post last year showed that grain-free, all-meat, and raw-food diets are one of the fastest growing sectors of the pet food market. It’s kinda like the Paleo Diet, but for pets. Trouble is, there’s no evidence that raw meat-based diets, or RMBDs, are any healthier than conventional dry or canned pet foods. And as new research published in Vet Record now shows, these diets could pose a threat to both animal and human health.

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A research team led by Paul Overgaauw at Utrecht University sought to learn if zoonotic bacteria and parasites, that is, bacteria and parasites that can leap between species, might be found in commercial RMBD products, and to what extent. To that end, they analyzed 35 commercial frozen RMBDs from eight different brands, all from the Netherlands.

What they found was a bit disturbing. The bacterium E. coli was found in nearly a quarter of the products, and Salmonella in 20 percent of products. Both of these pathogens are dangerous to humans and pets. In addition, the researchers found various Listeria species in 43 percent of the products—bacteria that’s particularly dangerous to pregnant women, newborns, the elderly, and people with weakened immune systems. Four of the products had the Sarcocystis cruzi and Sarcocystis tenella parasites (the former of which is transmissible to humans). And finally, two of the products had Toxoplasma gondii—a brain parasite that’s known to alter the behavior of animals, possibly even humans.

The researchers only tested products available in the Netherlands, which is a limitation to the study. These products will vary from country to country, each of which enforces different standards for meat, quality control, and so on. But studies done in other countries have reached similar conclusions (examples here, here, here, and here).

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People could come into contact with these pathogens by touching the infected pet, handling contaminated pet food and surfaces, or consuming human food that has been cross-contaminated. In addition to having owners educate themselves about the risks and engaging in good personal hygiene practices, the researchers advise that manufacturers include warnings and handling instructions on their products.

“Despite the relatively low sample size of frozen products in our study, it is clear that commercial RMBDs may be contaminated with a variety of zoonotic bacterial and parasitic pathogens that may be a possible source of bacterial infections in pet animals and if transmitted pose a risk for human beings,” write the researchers in their study. “Cats and dogs that eat raw meat diets are also more likely to become infected with antibiotic-resistant bacteria than animals on conventional diets, which could pose a serious risk to both animal health and public health.”

Jennifer Larsen, a clinical nutritionist at the University of California Veterinary School in Davis who wasn’t involved in the new study, agrees with the authors.

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“We do not recommend the feeding of raw animal products (meat, egg, bone, etc), and these types of diets are not allowed in the Veterinary Medical Teaching Hospital per our Infectious Disease Control Policy,” she told Gizmodo. “There are risks to both animal and human health as a result of this practice, with no proven benefits. This is backed by previous research that has found similar types of contamination in commercial raw pet diets, so the risks are well documented.”

Larsen pointed to policies and position statements regarding this issue from the American Veterinary Medical Association, the California VMA, the Canadian VMA, and the FDA (here, here and here).

Larsen is unconvinced by arguments stating that dogs and cats should be given foods that they’re more likely to eat in the wild.

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“The goals we want for our pets include longevity, usually not reproducing, ideal nutrition and good body condition, and avoidance of trauma and disease,” she said. “We do lots of things to protect them from what would happen in nature, such as starvation, disease, early and often reproduction, trauma from accidents and fights, and very short lifespan. We have the ability to do this thanks to scientific advancements in nutrition, medical therapy, and preventative veterinary care (neutering, vaccines), as well as the use of leashes and fences and moving them indoors.”

Importantly—and as Larsen points out—dogs and cats are not “natural.” We created them for our own purposes, using them for hunting partners, companionship, farm work, and so on.

“Since they essentially evolved on human garbage and have excelled at this scavenger lifestyle—and most dogs worldwide still live this way—it is not realistic to imagine them as wolves,” said Larsen. “Cats are closer to their undomesticated state, but we still want them to live long lives and not transmit diseases to us when they sleep in our beds and walk on our kitchen countertops!”

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Debbie Phillips-Donaldson, editor-in-chief of the Petfood Industry/Petfood Forum (a business-to-business publication with an audience of pet food professionals around the world, including people who make and market pet food), says her organization doesn’t advise pet owners on what they should feed their pets, but she did point us to a study by scientists from South Korea who found that “eating homemade raw dog food for more than a year correlated to different microbes thriving in dogs’ intestines compared to the guts of dogs fed store-bought dry kibble.”

“I will say this,” Phillips-Donaldson told Gizmodo. “Veterinary and regulatory experts do tend to warn about the risks to humans of feeding raw pet food, so many, if not most, companies offering raw diets take great pains to not only make sure their products are safe but also educate consumers about proper handling practices.”

She added that the raw pet food segment is one of the fastest growing, if still small—and despite the concerns.

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To ensure that our companion animals are safe, Larsen says pet owners should use cooked commercial diets (kibble and canned options are the most popular), or properly balanced, home-cooked diets for people with the money, space, and time resources to do so. “Either option is fine,” she told Gizmodo. Larsen also advised that pet owners use a service run by a board-certified veterinary nutritionist such as BalanceIT.com or contact a nutrition service at a veterinary school.

[Vet Record]