When most people think about Salmonella, images of raw eggs, pet reptiles, and supermarket recalls come to mind. But horse caretakers know this bacterium can cause serious – and sometimes life-threatening – diseases in their horses as well. It’s important that caretakers know the latest information about the disease and what they can do to protect their horses and themselves from infection.
Basic Biology
Salmonella is bacteria that have worldwide distribution and can be isolated from the intestinal tracts of many species of animals and humans. Although the bacteria prefer to live in the intestinal tract, Salmonella can persist in the environment, surviving weeks to years, but are susceptible to drying, UV light, freezing temperatures, and common disinfectants. They can survive adverse conditions if they are somewhat protected – for example in a crack or crevice, under a mat, in a fecal ball, etc.
Salmonella infects new individuals when they ingest the bacteria. The organism is common, and many infected animals (and people) show no clinical signs (subclinical infection). Evidence suggests that Salmonella is more likely to cause disease in horses exposed to high numbers of bacteria; or those that have strained or immature immune systems, such as foals or horses suffering from other illnesses.
The most common signs of Salmonella infection (salmonellosis) in horses include:
- Diarrhea
- Lethargy and poor appetite
- Fever
- Colic
Even in horses with no clinical signs, Salmonella can be shed through feces into the environment, providing a source of infection for other horses as well as for other animals and people. In addition, horses that have subclinical infections can develop clinical disease if they are stressed.
Diagnosis can be tricky
It might seem obvious that finding Salmonella in the stool of a sick horse would be a slam-dunk when it comes to diagnosis, but it’s not quite that simple.
Salmonella in a horse’s stool doesn’t mean it is the cause of disease, nor is it an indication for treatment if a horse is healthy (more on this later). Diagnosis requires careful consideration of clinical signs, history, and additional test results. Sometimes it can be challenging to identify Salmonella even when it is clinically important, and repeated testing might be necessary to pin down the diagnosis.
Treatment — one size doesn’t fit all
Treatment in clinically ill horses always includes supportive care measures such as IV fluids and electrolyte replacement, and gastrointestinal protectants.
It might seem counterintuitive at first, but not all horses need antibiotic therapy as part of their treatment protocol.
Antibiotics are indicated in cases where the chance of Salmonella entering the bloodstream is high, such as in horses with compromised immune systems. In horses that aren’t severely ill, or that have Salmonella noted in their feces but are not showing any clinical signs, there is no evidence that giving antibiotics improve long-term outcomes. Giving antibiotics to these horses can also contribute to the growing problem of antibiotic resistance.
Prevention and control can be difficult
Because Salmonella can exist in the environment for long periods, elimination of the organism in a stable or outside environment can be challenging.
Removing feces, harrowing to break up and spread any remaining feces (solution to pollution is dilution), and mowing grass to 4” to facilitate UV light penetration can help decrease this risk.
The idea is to decrease contamination to a level that is of minimal consequence to the average horse (i.e. make it unlikely for a horse to be exposed to an “infectious dose”). And greater effort may need to be placed on this if your horse is more susceptible to infections (i.e. immune compromised).
Isolation of infected animals is standard protocol when horses are treated in veterinary hospitals. Some experts recommend not allowing horses to eat off the ground at shows and events, and disinfecting shoes and any equipment. It’s also a good idea to isolate any new horses entering a new environment for two to three weeks, to ensure they’re healthy. A shorter period of isolation is also wise for horses returning to a farm after travel.
Knowing the facts about Salmonella can help you keep your horses happy and healthy!
Dr. Kelly Diehl received her DVM from the University of Tennessee and started her practice career in an emergency clinic in New Jersey. She then completed an internship at the prestigious Animal Medical Center in New York City, after which she moved west, completing a residency in small animal medicine at Colorado State University. Dr. Diehl joined the staff of the Veterinary Referral Center of Colorado as co-owner of the internal medicine section. After 14 years, she left private practice to pursue a career in medical communication and joined the Morris Animal Foundation team in 2013. Dr. Diehl is a board-certified small animal internal medicine specialist and a Certified Veterinary Journalist.
AUTHOR PROFILE
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