Experts are warning dog and cat owners to be aware of the risks associated with feeding their pets raw meat-based diets (RMBDs), instead of the more conventional dry or canned pet foods.

In the Vet Record today, a team of researchers based in The Netherlands say these diets may be contaminated with bacteria and parasites, and as such may pose a risk to both animal and human health.

Feeding RMBDs to companion animals has become increasingly popular across the world, yet claims of health benefits are not backed by evidence, and several studies have reported possible risks.

Of most concern, however, is the risk to public or animal health due to contamination of RMBDs with zoonotic bacteria and parasites, that can pass between animals and humans.

So a team led by Paul Overgaauw at Utrecht University set out to determine the presence of four zoonotic bacteria and two parasite species in commercial RMBDs, available in most pet shops and supermarkets.

They analysed 35 commercial frozen RMBDs from eight different brands, widely available in The Netherlands. Escherichia coli O157 was isolated from eight products (23%), Listeria species were present in 15 products (43%) and Salmonella species in seven products (20%). Both E coli O157 and Salmonella infections in humans have been linked with serious illnesses.

Four products (11%) contained the parasite Sarcocystis cruzi and another four contained Sarcocystis tenella. In two products (6%) Toxoplasma gondii was found. The Sarcocystes species are not zoonotic but pose a risk to farm animals. T gondii is an important zoonosis with a high disease burden in humans.

"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," say the researchers.

"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," they add.

They outline several ways in which pet owners and other household members can encounter such pathogens. For example, through direct contact with the food or with an infected pet; through contact with contaminated household surfaces; or by eating cross-contaminated human food.

They therefore suggest that pet owners should be informed about the risks associated with feeding their animals RMBDs, and should be educated about personal hygiene and proper handling of RMBDs.

Warnings and handling instructions should also be included on product labels and/or packages, they advise.