Do raw meat diets pose health risk for our pets and us?
Dr Vanessa M Schmidt (BVSc (Hons) PhD CertVD DipECVD MRCVS) and Professor Nicola J Williams (BSc (hons) PhD)
Feeding raw meat diets to companion animals, although a long-lived practice has recently become more popular due to the wide availability of commercial raw-meat-based-diets and the belief that they are more ‘natural’ and provide health benefits to dogs. A raw meat diet is more reflective of the domestic dog’s wild cousins, the wolf and therefore deemed to be more natural.
Regardless of the perceived benefits of raw meat diets, the question is whether the feeding of raw meat diets in a domestic environment poses a risk to dogs or their owners. It is well reported that raw meat can contain bacterial pathogens that can cause gastrointestinal disease, such as Campylobacter and Salmonella species. However, such diets may also act as a vehicle for transmission of antibiotic resistance with associated potential animal and public health risks, particularly for those at higher risk e.g. the young, elderly or immune-suppressed. Furthermore, sharing of gut bacteria e.g. Escherichia coli (E. coli) between people and pets in the household is well reported (Johnson et al., 2008).
Salmonella and Campylobacter infection in dogs is largely subclinical, with dogs shedding the infectious agent in their faeces without displaying any signs of disease. Colonised individuals can act as a source of infection to other pets and humans, particularly where proper hygiene protocols are not practiced (LeJeune and Hancock, 2001). However, Salmonella has been reported to be a significant cause of gastrointestinal disease (Morley et al., 2006) and caused considerable mortality amongst kennelled Greyhounds eating raw meat diets (Chengappa et al., 1993). Human campylobacteriosis has also been attributed to dogs (Kittl et al., 2013). In particular, contact with diarrhoeic or new pets, or contact between puppies and young children, although human and dogs may share strains the direction of transfer cannot be proven (Weese, 2011). Eating raw meat is a reported risk factor for the detection of canine faecal Salmonella (Joffe and Schlesinger, 2002; Lefebvre et al., 2008). In one controlled laboratory study, dogs fed a single salmonellae contaminated commercial and previously frozen raw-meat meal shed the bacteria in their faeces for up to 11 days, although they didn’t display any evidence of gastrointestinal disease (Finley et al., 2007). Freezing of meat should kill some bacteria, however it will not kill all bacteria present as the latter study demonstrated. Prolonged shedding of such bacteria could therefore be expected with regular raw-meat feeding (Joffe and Schlesinger, 2002).
Previous published studies investigating antibiotic resistant bacteria in the faeces of dogs at the University of Liverpool, demonstrated that the feeding of raw meat to dogs was a risk factor associated with the carriage of E. coli resistant to antibiotics which are important for treating infections in both humans and dogs (Schmidt et al, 2015, Wedley et al, 2017). One of these studies was done at scale, recruiting 580 dogs recruited nationwide (Wedley et al, 2017). Raw meat diets were also associated with faecal carriage of E. coli resistant to important antibiotics and Salmonella species in dogs in a further study in North America (Lefebvre et al., 2008).
This prompted our recent study* to investigate further the faecal carriage of antibiotic resistant E. coli and the human gastrointestinal pathogens Campylobacter and Salmonella species in dogs on raw and commercial cooked diets. Dogs were recruited for this study and a questionnaire used to obtain information about the dog, its household and diet. Faeces were examined for the presence of E. coli¸ Campylobacter and Salmonella species, and any bacteria identified were tested to see what antibiotics they were resistant to.
In total 190 dogs were recruited for this study, 114 on raw and 76 on cooked fed diets. It was found that dogs fed diets containing raw-meat were more likely to carry Salmonella species and antibiotic resistant E. coli compared to the control group (cooked diets), including E. coli resistant to multiple types of antibiotics, including those critically important to human health, such as the 3rd generation cephalosporins (31% of dogs on raw diets compared to 4% of dogs on cooked meat diets).
Antibiotic resistance is a growing concern within human and veterinary medicine. Dogs and humans may harbour bacteria with resistance in their gut, if these bacteria cause an infection, or the resistance is passed onto other more pathogenic bacteria which cause an infection, antibiotic treatment may fail. Further evidence on the risk of raw meat feeding from large cohort studies are required, in particular to determine the nutritional benefits and to further examine the pet and human risk from bacterial faecal shedding. However, funding for such studies is difficult to obtain to do such work on scale and derive bigger samples of dogs on a range of diets. Contrary to the beliefs of some, commercial food companies will not fund such work, due to conflict of interest.
Till further studies and data is obtained, thorough hand hygiene is strongly recommended after handling raw meat and thorough disinfection of all in-contact items as per normal handling of raw meat in a domestic kitchen. Furthermore, it is important to restrict the area where raw meat is fed to avoid any bacteria present on the meat being spread around the household environment and acting as a source of infection. In addition, it is recommended that, households which have very young or old members, or those who are immunocompromised and therefore more susceptible to illness should avoid feeding their animals raw meat diets completely.
Conflict of Interest; Neither Vanessa Schmidt or Nicola Williams have received any funding from commercial food companies for this or other work.
*Study carried out in 2015/16. Findings presented at BSAVA 2016 conference and in the process of publication.
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Finley, R., Ribble, C., Aramini, J., Vandermeer, M., Popa, M., Litman, M., Reid-Smith, R., 2007. The risk of salmonellae shedding by dogs fed Salmonella-contaminated commercial raw food diets. Can Vet J48, 69-75.
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