Issues Associated with Salmonella in Pet Foods

By Angela Ellis, DVM, PhD & Susan Sanchez, BSc, MSc, PhD, MIBiol, CBiol

Earlier this year, an outbreak of salmonellosis was associated with tainted peanut butter products from the Peanut Corporation of America, and products are still being recalled as this article is being written. Although most of the products involved were for human consumption, some dog biscuits, rawhides, and other pet treats were among the recalled items. In addition, many pet owners admitted to having fed peanut butter crackers and other recalled human foods to their pets. Given recent deaths in animals due to melamine/cyanuric acid and aflatoxin contaminated dog and cat foods, it is understandable that owners are concerned about food recalls. However, Salmonella-contaminated pet treats and foods actually pose a risk to owners as well as to their pets.

Although most animals are susceptible to infection with Salmonella, infection does not necessarily result in clinical disease. In dogs and cats, a carrier state is far more common than clinical disease. Salmonella has been isolated from feces of 1-36% of healthy dogs and 1-18% of healthy cats, and the actual prevalence of infection is probably higher than these estimates. Dogs and cats with healthy immune systems or that are infected with low numbers of organisms typically do not develop clinical signs or will have only mild, transitory illness.

Clinical disease, when it occurs, may include gastroenteritis, bacteremia with or without endotoxemia, abscesses, pyothorax, meningitis, osteomyelitis, cellulitis, mucoid or bloody diarrhea, abortions, stillbirths, or birth of weak puppies/kittens. Fewer than 10% of infected dogs and cats die during the acute phase of Salmonella infection. Clinical signs are more often than not associated with stress. Stress may also increase shedding of Salmonella in healthy companion animals.

Salmonella may persist in intestinal epithelial cells and lymphoid tissue, and infected animals typically shed bacteria for 3-6 weeks and rarely up to 12 weeks. Phagocytic cells in the spleen, liver, and lymph nodes may harbor bacteria even longer, and animals may become persistently infected. These animals may then start to shed bacteria again following episodes of immunosuppression due to stress, certain drugs, or systemic diseases.

Humans are more susceptible to clinical disease than are dogs and cats, and salmonellosis can be a serious disease in infants, the elderly, and those with poor immune systems. In addition to possible exposure from fecal shedding of Salmonella from asymptomatically infected pets, owners may also be exposed to Salmonella directly through handling of contaminated food. This occurred previously in 2006-2007 when 70 people became ill with a strain of Salmonella (S. schwarzengrund) that was traced back to contaminated dry dog food. Earlier outbreaks have been associated with contaminated pig ears and dog treats containing dried beef or seafood.

Pet food is one of the highest risks for pet owners as many of these foods may be contaminated with pathogenic Salmonella, but we assume that food is safe and it is very unlikely we engage in hand washing after handling such products.

The Centers for Disease Control and Prevention recommends the following steps to prevent Salmonella infections. Persons should wash their hands for at least 20 seconds with warm water and soap immediately after handling dry pet foods, pet treats, and pet supplements, and before preparing human food and/or eating. Infants should be kept away from pet feeding areas. Children under 5 years should be kept away from pet food, treats, or supplements.

The Athens diagnostic laboratory has a Salmonella diagnostic test that is more sensitive than culture that can help identify healthy carriers. These newer molecular tests allow for diagnosis and carrier identification within 24 hours. Furthermore, once the organisms are cultured we can type isolates and determine if they are in any way associated with the current human outbreak strains.

Data thus far from the past year does not indicate an increase in isolation of Salmonella of any serotype from clinically sick dogs. None of past isolates have been of the serotype Typhimurium currently involved in the outbreak. If you have any questions on how to submit samples or determining the most appropriate test, please call Dr. Susan Sanchez, section head of Microbiology and Molecular Diagnostics at the AVDL 706-542-5568.

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