What is Salmonellosis in Horses?

Salmonellosis is a disease associated with the bacteria Salmonella enterica that causes diarrhea in horses and humans. It is usually seen sporadically but may become an epidemic depending on the virulence of the organism, level of exposure, and host factors.

In horses, the bacteria are transmitted through contaminated feed or water, or by direct contact with infected individuals or surfaces that have been contaminated with manure from an infected individual. Mice, barnyard chickens, pigeons, and wildlife can be sources of Salmonella. Some horses are carriers that do not show any signs of disease but can actively transmit the organism.

Stress appears to play an important role in the progression of the disease. Surgery, transportation, or changes in feed, concurrent disease (particularly gastrointestinal disorders such as colic), or treatment with broad-spectrum antimicrobial drugs often precede diarrhea. Asymptomatic carriers can become sick when under stress. Severe cases can be fatal if not treated.

Clinical Signs 

The clinical signs of salmonellosis in adult horses can include diarrhea, lethargy, fever, anorexia, and colic. Affected horses may be more susceptible to infection. Once recovered, these horses may continue to shed the bacteria in their feces, potentially transmitting it to other horses.

Some adult horses are subclinical shedders that do not show clinical signs but have the potential to transmit the bacteria to susceptible horses by direct contact or contamination of feed, water, or the environment. If stressed, carriers may develop clinical signs.