Salmonellosis refers to infection with Salmonella, a bacterium that primarily causes intestinal infections and diarrhea in mammals. Salmonella can affect numerous species, including horses and humans. Horses typically acquire the bacteria by ingesting contaminated feed or water.

Common symptoms of salmonellosis in horses include diarrhea, fever, and lethargy. In some cases, Salmonella can cause sepsis (blood infection), which can be life-threatening. Veterinarians use a fecal or blood sample to identify the bacteria and make a diagnosis.

Treatment of Salmonella infection often requires hospitalization and intensive care. Fluid therapy, antibiotics, and toxin neutralization products are components of many treatment protocols. The prognosis for horses with Salmonella infection depends on the severity of disease, with outcomes ranging from excellent to very poor.

Preventative measures focus on reducing exposure to Salmonella through environmental management, hygiene, and quarantine of new arrivals.

Salmonella Infection in Horses

Salmonella bacteria are a common intestinal pathogen (disease causing agent) associated with diarrhea and intestinal infections in many species. [1] The most common intestinal strains of Salmonella in horses are Typhimurium, Newport, and Agona. [1]

Horses also have a host-adapted strain of this bacteria, S. Abortusequi, which only affects horses. [1] This strain causes abortions in affected broodmares and sepsis (blood infection) in newborn foals. [1]

Most horses acquire Salmonella from their environment. [1] Possible exposure routes include: [1]

  • Ingestion of contaminated feed
  • Ingestion of feces from mice or birds
  • Consuming contaminated water
  • Contact with contaminated surfaces, including the hands of handlers
  • Contact with livestock species shedding Salmonella

Once ingested, Salmonella bacteria attach to the intestinal lining and inject bacterial proteins into the intestinal cells. [1] These proteins trigger transfer of the bacteria from the intestinal lining into the bloodstream. [1] If not controlled by the immune system, the transfer of bacteria can result in sepsis.

Infection of intestinal cells also triggers inflammation of the intestine, resulting in cell damage. [1] This inflammation triggers fluid secretion into the intestines, causing the increased fecal fluidity associated with diarrhea. [1]

Additionally, damage to the intestinal cells allows protein within the bloodstream to enter the intestines, resulting in hypoproteinemia (low blood protein). [1] One of the major roles of proteins in the body is preventing fluid from leaving the bloodstream, meaning that hypoproteinemia further increases fluid secretion and worsens diarrhea. [1]

Risk Factors

Not all horses develop symptoms after infection with Salmonella. [1] Risk factors for developing infectious symptoms after Salmonella exposure include: [1][2][3][4]

  • Age: young horses have a higher risk of developing symptoms compared to adults
  • Stress: horses experiencing stress are more likely to develop disease; including stressful events such as transportation, surgery, feed changes, or other illnesses
  • Intestinal flora: horses with healthy intestinal flora are less likely to develop symptoms
  • History of antibiotic use: antibiotics may disrupt the intestinal flora and make Salmonella infection more likely
  • History of hospitalization: equine hospitals may have a high burden of Salmonella in the environment, increasing the likelihood of infection; in particular, horses undergoing abdominal surgery have the highest risk of infection after hospitalization