A study by Erin Leonard of the University of Guelph and others, that has just been published in the journal Zoonoses and Public Health, once again points to the increased risk of Salmonella shedding associated with feeding raw diets to dogs.  The study looked at 138 dogs from 84 households in Ontario.  One-quarter of households (21/84, 25%) had at least one dog (32/138, 23.2%) that was shedding Salmonella at one time, which is considerably higher than the 1-4% of pet dogs that are typically expected to be shedding this zoonotic pathogen.  Only 4 of the 32 positive dogs had any history of diarrhea in the last month, so the vast majority of these dogs had no signs that they were shedding Salmonella.  Here were the study’s main findings:

1. Consuming a commercial or homemade raw diet, a homemade cooked diet, or raw meat and eggs, increases a pet dog’s risk of carrying Salmonella.

Raw is raw, and by now we’re hoping that people are getting the message that raw is contaminated, whether we’re talking about a commercial or homemade raw diet, or feeding any raw animal products (e.g. meat, eggs).  The fact that homemade cooked diets also made the list could be explained by the fact that in order to make such a diet, owners still need to start with the raw ingredients.  Handling and cooking raw meat and animal products for your pet should be done with the same precautions as handling and cooking raw meat for yourself or your family.  If these homemade diets were not cooked as thoroughly as they should have been, or if there was contamination of the dog’s dishes with raw product, that could explain the association with Salmonella shedding.  Although traditional commercial diets can also be contaminated with pathogens (usually after processing), the risk with these is much lower.

2. Testing multiple consecutive whole fecal samples greatly improves Salmonella recovery in dogs.

This is no great surprise either.  Dogs (and many other species) shed Salmonella intermittently, so not every fecal sample from a Salmonella-positive dog is going to yield Salmonella on culture.  The authors tested five daily fecal samples from each dog.  Based on this study, the sensitivity of testing a single fecal sample in a dog (i.e. the likelihood that a Salmonella-positive dog will test positive on one fecal sample) was only 35.5%.  That means almost two-thirds of positive dogs will be missed if they’re only tested once.  The take-home message on this point is that in order to find Salmonella in a healthy pet dog, multiple samples should be tested.

3. Having multiple dogs in a household, using probiotics and contact with livestock are important potential risk factors that need to be investigated further.

These were factors that were flagged by the authors for future investigation, because at first they seemed to be associated with Salmonella shedding in the dogs, but when the feeding of raw diets was taken into account the associations were no longer significant.  A larger study, or one using a different design, will be needed to help tease apart the potential effects of these factors from feeding practices.

The bottom line: Feeding raw is risky business.  Some people swear by the benefits of raw diets, but the objective evidence is lacking.  There is clear evidence of the risks.  In my mind, the potential up-side simply cannot outweigh the well-established down-side of feeding raw diets to pets.