Overview of Listeria in Dogs
Listeria is a food borne bacterial illness caused by the bacterium Listeria monocytogenes which can infect humans as well as dogs and cats. Listeria is a bacteria found in soil, water, and in some animals, including poultry, cattle, sheep and goats. It can also be found in rabbits, guinea pigs, and other species.
Dogs can be infected with Listeria by the same sources as human exposure, including infected meats and dairy product as well as contaminated dog food. There have been various pet food recalls due to contamination with listeria including the Bravo Pet Food Recall in May 2014.
Dogs fed raw diets are at a higher risk for Listeria infection. The U.S. Food and Drug Administration (FDA) cites a two-year study from October 2010 through July 2012 by the FDA Center for Veterinary Medicine (CVM). In the study, over 1,000 samples of pet food were screened for bacteria that can cause foodborne illnesses. The FDA stated “The study showed that, compared to other types of pet food tested, raw pet food was more likely to be contaminated with disease-causing bacteria.” The participating laboratories analyzed the raw pet food for harmful bacteria, including Salmonella and Listeria monocytogenes.
Infection with Listeria, commonly called Listeriosis, can cause severe infection in pregnant women, elderly people and humans with suppressed immune systems. Healthy people and dogs are rarely infected.
Many aspects of the disease spread, symptoms, diagnosis, treatment and prevention in humans are the same as those in dogs.
Sources of Listeria
Dogs can be exposed to Listeria from contaminated dog foods as well as eating contaminated garage.
Listeria can be present in raw milk and foods made from raw milk and contaminate a variety of processed meats and dairy products. Unlike many other bacteria, Listeria can grow in refrigerated temperatures and even spread to other foods in the refrigerator which makes it a challenging organism. However, Listeria is killed by pasteurization and cooking.
Common sources of Listeria in dogs include:
- Raw pet food diets
- Contaminated dog food
Dogs fed table scraps that are contaminated. Sources of human foods associated with Listeria include:
- Raw vegetables (that have been contaminated from the soil from contaminated manure used to fertilize the soil) or deli-prepared salads.
- Infected animal meats such as from deli meats, hot dogs, meat spreads
- Dairy products such as ice cream
- Unpasteurized milk or foods made with unpasteurized milk
- Soft cheeses e.g. Feta, Brie, Camembert, Panela, Queso fresco and other blue-veined cheeses.
- Smoked refrigerated seafood
Can Dogs Spread Listeria to People?
According to the Ontario Veterinary Medical Association, “It is highly unlikely that a dog that has eaten contaminated meat would pass the infection on to humans. A small percentage of healthy pets can shed Listeria in their stool at any time.”
Our research suggests that dog to human contact is unlikely. Most human infections are directly from the list above including contaminated meat and dairy products.
Listeria can be spread by eating the bacteria, direct contact or by inhalation.
Diagnosis of Listeria in Dogs
Blood tests can confirm the diagnosis of Listeria. For dogs with neurologic symptoms, analysis of the cerebrospinal fluid can also be suggestive of infection.
Symptoms of Listeria in Dogs
Symptoms can vary with the individual dog, from no symptoms, very mild flu-like symptoms to severe neurologic symptoms. Not all dogs exposed to listeria will develop symptoms or become ill.
Symptoms may include: Diarrhea, nausea, vomiting, weakness, fever, muscle soreness, lethargy, lack of coordination, and/or a stiff neck. A severe consequence of Listeria is meningitis which is a disease of inflammation of the membranes covering the brain and spinal cord. In addition to the above, infection of pregnant women can cause miscarriage; stillbirth or the baby can be born with a life-threatening infection. The same things are believed to be true of dogs. Listeria has also been shown to cause skin infections in dogs.
How Long Does it Take to Show Symptoms of Listeria
Due to the infrequent diagnosis in dogs, the incubation period of Listeria is unknown. In humans, it can take as little as 2 to 3 days from the time you are exposed to Listeria to show to as long as 2 months (70 days). The same is believed to be true in dogs.