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Salmonella

Most people have heard of the bacterial pathogen Salmonella. It causes a common foodborne illness in humans (mild to severe digestive upset) after consuming contaminated undercooked meat or unwashed vegetables. Salmonella is also a concern for dogs who may get diarrhea from the infection and then shed these bacteria in their stools. For dogs with symptoms of digestive upset, include screening by PCR (ClueJay Dog Stool Test Level 3) as a reliable way to search for Salmonella and other disease-causing microbes found in dog intestines.

Salmonellosis is a disease of major zoonotic importance. It is easily transmissible between pets and people and causes disease in both human and animals.

Green Infectious Diseases of the Dog and Cat

All About Salmonella

What Are Salmonella?

Salmonella enterica are bacteria with over 2000 subtypes. Salmonella are microscopic so cannot be seen by the naked eye. They are a major cause of foodborne illness in humans and pets around the world.[1,2]

Salmonella belongs to a large family of intestinal bacteria called Enterobacteriaceae (enteric bacteria) which includes both harmless bacteria and familiar pathogens, including E. coli (Escherichia coli), Klebsiella, and Shigella. Salmonella are intestinal parasites but, in some circumstances, will migrate into the bloodstream (septicemia) or organs to cause more widespread illness in the animal. They are facultative anaerobes, meaning they can survive both with oxygen (e.g., on raw meat) and without oxygen (e.g., within the intestines).

A common source of Salmonella infection for pets is being fed uncooked or unprocessed foods.[6]  Even if pet owners are not feeding raw foods, dogs can get infected with Salmonella from eating animal stool or things contaminated by the stool (water, soil, grass, plants). Fortunately, Salmonella doesn’t usually make dogs sick.[4] Many dogs can carry and shed these bacteria into their stool without any signs of illness. This ongoing or occasional shedding can lead to infecting other pets or people through direct physical contact or indirectly from stool contamination.

People also can get infected by accidently consuming food or water that was contaminated with Salmonella from human or animal stool.[5] A common human source of infection is raw meat (swine, cattle, turkeys, horses, chicken) sold in the U.S. for consumption by people or animals.[6]

How Common Are Salmonella?

The frequency of Salmonella identified from healthy (no symptoms) or hospitalized dogs is reported to be 1% to 36% and from healthy cats is 1% to 18%.[6] A different study found that of 3,000 dog and cat samples from around the country (some with diarrhea and some without), less than 1% of cats and 2.5% of dogs were positive.[3,4] These percentages are interesting but less important than the risk factors of individual pets and families.

It’s important to recognize from this that many dogs and cats carry and shed Salmonella without showing any signs of illness. This prevalence is believed to be decreasing over recent decades because more pets are being fed commercially produced foods.[6]

Salmonella infects all sorts of mammals, birds, reptiles, and insects. Some types of Salmonella prefer certain animal hosts while others can be harmful to more than one kind of animal. Salmonella enterica typhi for example, is usually harmless to animals but causes typhoid fever in people.[6] Salmonella enterica typhimurium on the other hand is easily transmissible and causes disease in both humans and animals.[6] This type is often a contaminant of raw meat (swine, cattle, turkeys, horses, chicken) sold in the U.S. for consumption by people or animals.[6]

Research has shown that 80% of raw chicken sold for animal consumption was contaminated with Salmonella, while 20-35% of poultry carcasses intended for human consumption was contaminated.[6] Some imported commercial dog chews made from animal hides and animal-derived dog treats sold in the U.S. have been found with Salmonella, some of which were multi-drug resistant strains.[6]

These bacteria can survive for long periods of time in the environment and multiply quickly in moistened food left at room temperature.[6] The most common source of infection is ingesting Salmonella from food, water, or surfaces that were contaminated with fecal (stool) matter like pet food dishes. Surfaces like countertops contaminated from raw meat preparation also represent a human and pet infection risk.

What Does Salmonella Look Like?

Salmonella are motile with hair-like projections that help them move. They are shaped like fat little rods (called bacilli) and not circle-shaped (called cocci) or spiral-shaped (called spirochetes). They belong to a large family of gram-negative, rod-shaped, enteric (intestinal) bacteria called Enterobacteriaceae. Salmonella are microscopic so cannot be seen by the naked eye.

Gram staining is a classic benchtop method for distinguishing types of bacteria in a sample (Gram negative versus Gram positive), staining them either pink (negative) or purple (positive) on a microscope slide. Salmonella stain pink (Gram negative) with this method.

Bacteria are not visible on a fecal O&P (ova (egg) and parasite) stool test (included in ClueJay Dog Stool Tests Level 1, 2, and 3). The O&P looks for worms and some types of coccidia, not bacteria. While Gram staining stool (fecal smear) can be helpful when searching for a bacterial cause of abnormal stools (diarrhea), the specific type of bacteria like Salmonella cannot be reliably identified in this way. Most of the time, a special Polymerase Chain Reaction (PCR) test is used to detect the presence of this parasite in dog stool (ClueJay Dog Stool Test Level 3).

What Symptoms Are Caused By Salmonella?

Fortunately, Salmonella doesn’t usually make dogs sick.[4] Many dogs can carry and shed these bacteria into their stool without any signs of illness. This ongoing or occasional shedding can lead to infecting other pets or people through direct physical contact or indirectly from stool contamination.

Dogs are more likely to get sick from Salmonella if they are younger than one year of age, and be life-threatening in very young puppies or unborn fetuses.[6] Nutritional deficiencies, overeating (overweight), stress from overcrowding, cancer, other simultaneous infections, a weakened immune system, steroid therapy, and antibiotic use are all risk factors for Salmonellosis (disease from Salmonella).[6] Ingesting a large concentration (number) of Salmonella can increase the number of bacteria that survive passing through the acid of the stomach, increasing the risk of illness.[6]

Dogs sick from Salmonella usually have signs of digestive upset like diarrhea (which may be bloody or with mucus), vomiting, loss of appetite, decreased activity level, and fever.[1,3] The diarrhea may come and go and may last for weeks or longer each time.[1] Severe symptoms like electrolyte imbalances, vomiting that won’t stop, shock and even death can result if Salmonella gets into the dog’s bloodstream or organs.[1,3]

For people, illness usually appears 12-72 hours after infection.[3] Symptoms include fever, abdominal pain, diarrhea, nausea and vomiting lasting 4-7 days.[3] Most people will recover without treatment.

How Do Dogs Get Salmonella?

Salmonella can survive for long periods of time outdoors. Stool from dogs and other animals shedding the bacteria can contaminate water sources frequented by pets. Dogs may also ingest the bacteria when eating stool from other dogs or animals (rodents, livestock, wildlife) while in the backyard, out for walks, in dog parks, etc. One dog can spread Salmonella to other dog (and cat) housemates or be exposed to contaminated stool when housed with other dogs like kennels, day cares, or shelters. [1,2]

Salmonella enterica typhimurium (the most common type) is easily transmissible between pets and people and causes disease in both humans and animals.[6] Salmonella can contaminate raw food or treats, with raw meat (swine, cattle, turkeys, horses, chicken) being a major risk factor for infection.[3,4] Uncooked or unprocessed foods also pose an increased risk to the humans handling it. Salmonella can multiply quickly in moistened food left at room temperature.[6] Surfaces exposed to the contaminated food like food dishes and countertops for raw meat preparation also represent a human and pet infection risk. Imported commercial dog chews made from animal hides and animal-derived dog treats sold in the U.S. have been found with Salmonella, some of which were multi-drug resistant strains.[6]

Puppies may contract Salmonella from their mother in the womb or after being born.[3]

What Is The Salmonella Life Cycle?

Dogs can ingest Salmonella from eating contaminated food or treats (uncooked or unprocessed) or animal stool, or ingesting water, soil, or vegetation (grass, plants) contaminated from stool (fecal material) in the environment.

A high concentration (number) of Salmonella must be ingested for the bacteria to infect a dog. This is because a large portion are destroyed by the acid of the stomach.[6] The bacteria that get through colonize the small intestine by attaching to the hair-like covering (microvillous) of the digestive tract lining. The Salmonella use their hair-like projections to bury into the cells and local lymph nodes.[6] They may also get into and persist in the liver and spleen.

After initial infection, shedding lasts for about 3-6 weeks.[6] Most dogs become healthy carriers of the bacteria while others can get quite sick. Shedding of Salmonella in stool can be reactivated later with stress, overcrowding, weakened immune system, or other infections.

Beyond invading the cells of the intestines, Salmonella causes inflammation and can release damaging toxins (enterotoxins). They can also enter the bloodstream (bacteremia) and get spread throughout the body, causing widespread inflammation and toxin release. These more severe infections can lead to fever, toxic shock, and even death.[6]

Salmonella infects dogs, cats, people, and all sorts of other mammals, birds, reptiles, and insects. Some types of Salmonella prefer certain animal hosts while others can be harmful to more than one kind of animal. Salmonella enterica typhimurium (the most common type) is easily transmissible between pets and people. It can cause disease in both humans and animals.[6]

Can People Or Other Pets Get Salmonella?

Yes. Salmonella is a serious human health concern.[5] These bacteria have been a known cause of illness in humans for over a century.[3]

Salmonella infects dogs, cats, people, and many other types of animals.[1] Some types of Salmonella prefer certain animal hosts while others can be harmful to more than one kind of animal. Salmonella enterica typhi for example, is usually harmless to animals but causes typhoid fever in people.[6] Salmonella enterica typhimurium on the other hand is easily transmissible between animals and people and can cause illness in both.[6]

People get infected by accidently consuming food or water that was contaminated with Salmonella from human or animal stool.[5] A common human source of infection is raw meat (swine, cattle, turkeys, horses, chicken) sold in the U.S. for consumption by people or animals.[6]  Research has shown that 80% of raw chicken sold for animal consumption was contaminated with Salmonella, while 20-35% of poultry carcasses intended for human consumption was contaminated.[6] Other sources include unwashed fruits and vegetables, unpasteurized milk and other dairy products, raw or undercooked eggs and egg products.[3] Surfaces exposed to the contaminated food like food dishes and countertops for raw meat preparation also represent a human infection risk.

For people, illness usually appears 12-72 hours after infection but can take weeks to develop.[3,5] Symptoms include fever, abdominal pain, diarrhea, nausea and vomiting lasting 4-7 days.[3] Most people will recover without treatment. Children under 5 years old, the elderly, and people with weakened immune systems (e.g., HIV, chemotherapy, illness) are at higher risk of more severe infections.[5]

Most dogs infected with Salmonella become healthy carriers of the bacteria but can shed Salmonella in their stool intermittently, serving as a source of contamination for other dogs, cats, and people.

How Is Salmonella Prevented & Treated?

Feeding commercially available heat-processed dog food helps avoid Salmonella infection compared to raw or unprocessed diets.[6] Meat, eggs, and dairy products should be stored below 40 degrees and cooked to over 165 degrees Fahrenheit.[6] Also carefully source commercial dog chews made from animal hides and animal-derived dog treats since some have been found with Salmonella.[6] Good handling sanitation and storage of dog food is important, especially with raw food diets.

Pet owners feeding raw or unprocessed foods to their dog should consider health risks to the pet and family. 1) Since a high percentage of raw meat purchased for people or pets in the U.S. is contaminated with Salmonella, home surfaces like countertops for raw meat preparation and pet food dishes will represent a daily human infection risk. 2) Salmonella is a Gram-negative pathogen with a tendency to develop multi-drug resistance (MDR) to antibiotics. The Salmonella on the raw food might already have MDR, and these bacteria can be shared between pets and the human family. 3) Most dogs can be healthy carriers of Salmonella while shedding the bacteria in their stool, but some dogs and puppies can get quite ill. 4) Some human family members like children under 5 years old, the elderly, or those with weakened immune function are at much higher risk of illness from Salmonella. 5) It can be difficult to eradicate once in the environment.

Even if pet owners are not feeding raw or unprocessed foods, dogs may ingest the bacteria when eating stool (on soil, grass, plants) from other dogs or animals (rodents, livestock, wildlife) while in the backyard, out for walks, in dog parks, etc. Salmonella can last for extended periods of time outdoors and indoors. Cages in hospitals, kennels, and shelters should be cleaned and disinfected routinely. Household bleach (diluted 1:32, or 4 oz per gallon of water)[6] can be used as a surface disinfectant after cleaning and allowed to fully dry before reintroducing pets to the area.

Treatment is based on the severity of symptoms. Antibiotic therapy is not recommended for dogs who have no symptoms or mild signs that respond to supportive therapy like hydration, rest, and digestive support. This is because of Salmonella’s tendency for multi-drug resistance (MDR) and risk of passing this MDR to people. For dogs that require more assertive therapy, some antibiotics can be effective against Salmonella including trimethoprim-sulfonamide and amoxicillin.[6] However, these should not be given without a veterinarian’s prescription and supervision. In more severe cases, hospitalization, fluid therapy, and other treatments may be required. If your dog is sick, you should contact a veterinarian immediately.

Where Are Salmonella Medications Purchased?

ClueJay does not dispense or prescribe medications, and there are no FDA-approved medications in the U.S. for Salmonella treatment. Therapy is based on the severity of symptoms. Antibiotic therapy is not recommended for dogs who have no symptoms or mild signs that respond to supportive therapy like hydration, rest, and digestive support.

For dogs that require more assertive therapy, some antibiotics can be effective against Salmonella including trimethoprim-sulfonamide and amoxicillin.[6] However, these should not be given without a veterinarian’s prescription and supervision.

Important: Salmonella can develop multi-drug resistance (MDR) to antibiotics and then transfer those genes of resistance to Salmonella of the same type, to Salmonella of different types, and to other kinds of bacteria.[6] Since this bacteria can be shared between pets and people, pressuring Salmonella with antibiotic treatment can lead to the development of antibiotic resistance (especially if inappropriate selection or administration of antibiotics). This can lead to drug resistant Salmonella in the pet but potentially also in the human family.

While it is always best to consult with a veterinarian prior to administering any medication, even an OTC version, it is especially true for off-label treatment of Salmonella given the risk of antibiotic resistance. Always read the medication administration directions carefully and be on the lookout for potential side effects (like vomiting) when any medication is administered.

When/How is Dog Stool Tested For Salmonella?

Simply put, include a PCR test for Salmonella whenever a dog has frequent or ongoing abnormal stools (soft stool or diarrhea) or other digestive problems. Need details? Read on.

ClueJay Dog Stool Test Level 3 includes a Salmonella by Polymerase Chain Reaction (PCR) assay along with PCR tests for other disease-causing protozoa, bacteria, and viruses found in dog intestines. These tests are designed to find the DNA of hard to find microbe pathogens. Screen for Salmonella in dogs with signs of digestive upset like diarrhea (which may be bloody or with mucus), vomiting, loss of appetite, decreased activity level, and fever.[1,3]

Most of the time, Salmonella infections are not discovered unless veterinarians are searching for the cause of diarrhea or other digestive problems in dogs or puppies. Once found, vets may encourage pet owners to test other pets in the same household to determine if they are also shedding Salmonella.

Veterinarians recommend stool (fecal) testing puppies 2 to 4 times during their first year of life, and 1 to 2 times each year in adult dogs (every 6 to 12 months). Veterinarians often call this stool health test a “Fecal O&P”, with the O&P meaning “ova (eggs) and parasites”. It includes special preparations of the stool sample and analysis using a microscope to look for roundworms, hookworms, tapeworms, whipworms, and some types of coccidia. Bacteria are not visible on a O&P stool test (included in ClueJay Dog Stool Tests Level 1, 2, and 3). Most of the time, a microbe by PCR test is used to detect the presence of this parasite in dog stool (ClueJay Dog Stool Test Level 3).

With ClueJay’s simple and intuitive testing solution from home, you can directly access this same professional reference lab testing for Salmonella that veterinary professionals use commonly.

My Dog Tested Positive for Salmonella?

ClueJay Dog Stool Test Level 3 includes PCR assay tests for disease-causing bacteria, viruses, and protozoa found in dog intestines. One of those bacteria is Salmonella. A positive test means Salmonella DNA was detected in the stool. Most veterinarians then assume the dog is infected with Salmonella (called Salmonellosis) and shedding the bacteria in the stool.

However, your dog may not need treatment because this finding is not always associated with symptoms of illness. Most dogs infected with Salmonella will quickly suppress the parasite and never get sick or only have mild symptoms. Positive dogs may shed Salmonella occasionally so good hygiene practices and risk to family health from these bacteria should be reviewed.

A test result is not the same as a veterinarian’s diagnosis, so it’s always best to consult with a veterinarian about your dog’s test results to determine the safest and most effective treatment and prevention plan, and when to do follow-up stool tests. If treated, most veterinarians will recommend rechecking a dog’s stool sample within 2-4 weeks after treatment for Salmonella. If you have other pets (dogs or cats) in the household, consider testing them well since Salmonella in one pet can often lead to Salmonella in others.

It’s important to know that some dogs will continue to test positive for Salmonella for an unknown period of time after treatment. This is most likely because the dog remains in an environment where re-infection keeps occurring, but not always. Other considerations for treatment failure are poor immune response and drug resistance.[6]

ClueJay Dog Stool Test Levels 1, 2, and 3 include a reference lab stool O&P (fecal ova and parasites) which screens for roundworms, hookworms, tapeworms, whipworms, and some types of coccidia. Bacteria (including Salmonella) are not visible on this type of test which is why PCR testing (ClueJay Dog Stool Test Level 3) is needed.

Please consult your healthcare professionals if you are pregnant, immune-compromised, or have any concern about the risk of Salmonellosis.

My Dog Tested Negative for Salmonella?

ClueJay Dog Stool Test Level 3 includes PCR assay tests for disease-causing bacteria, viruses, and protozoa found in dog intestines. One of those bacteria is Salmonella. A negative test means Salmonella DNA was not detected in the stool, which is great news. No one wants their dog or puppy shedding these bacteria and maybe putting other pets or people at risk of infection.

Depending on their lifestyle, dogs can remain at risk of Salmonella exposure so a negative test result today doesn’t mean it couldn’t be positive later. Since dogs may shed these bacteria occasionally, it’s possible to test a stool sample from an infected dog without any of this parasite’s DNA. This is called a “false negative” when the test result is negative, but the dog is infected.

If Salmonella infection was suspected and you have other pets in the household, consider testing them as well since Salmonella in one pet can often lead to Salmonella in others. Dogs negative on Salmonella by PCR but still with Salmonella-like symptoms such as abnormal stools, likely have a different explanation for the symptoms. Please consult with a veterinarian if this is the situation with your dog.

Sources

  1. PetMD, Salmonella Infection in Dogs
  2. World Health Organization, Salmonella
  3. U.S. Food & Drug Administration, Get the Facts about Salmonella
  4. Reimschuessel R, Grabenstein M, Guag J, et al. Multilaboratory Survey To Evaluate Salmonella Prevalence in Diarrheic and Nondiarrheic Dogs and Cats in the United States between 2012 and 2014. J Clin Microbiol. 2017; 55(5):1350–1368.
  5. Centers for Disease Control and Prevention, Salmonella
  6. Greene Infectious Diseases of the Dog and Cat: Salmonellosis, 3rd ed. St. Louis, Elsevier Saunders 2006, pp. 355-360

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