Salmonellosis is a common cause of acute enterocolitis and diarrhea in the horse. However, equine diarrhea can be caused by many bacteria and Salmonella infection accounts for relatively few cases. Horses of all ages and under all conditions of management may be affected although the young, old and debilitated are the most susceptible. There are over 2000 Salmonella types of bacteria, not all of which can cause disease in animals. A small number have been isolated from horses, and Salmonella Typhimurium is by far the most common type identified from clinical disease.
Salmonella infection in horses is manifest as a variety of clinical signs. These range from acute diarrhea in young horses; a shock-like condition without diarrhea; mild to severe abdominal pain mimicking equine colic episodes where diarrhea may or may not develop; and protracted diarrhea.
Equine salmonellosis is commonly associated with stressful conditions such as transport, exhaustion, general anaesthesia, surgery, antibiotic or deworming medications, change in feed or management or weaning. These events may precipitate changes in food intake, bowel movements and in the normal intestinal microbial flora allowing overgrowth of Salmonella which are present in the intestinal tract of many healthy horses. The development of the disease depends on the immune status of the horse, the bacteria type involved and the presence of external factors.
SIGNS
Acute diarrhea can occur at any age but is most prevalent in young performance horses. Signs include fever, depression, abdominal pain and dark red mucous membranes. Diarrhea, which may not appear for 2 to 4 days, is watery, foul-smelling, and may persist for up to 4 weeks despite therapy. The shock-like syndrome is more likely to occur in adult horses. Death can follow 6 to 12 hours after the first appearance of abdominal signs. Very young foals may develop an acute generalized infection (septicemia). Older foals may have severe enteritis followed by spreading of the bacteria to joints, the growth region of bones, the lungs, kidneys or central nervous system. Chronic diarrhea is rarely attributed to Salmonella infection but can represent the recovery phase after an acute episode.
Confirmation of Salmonella infection depends upon isolating the organism from the feces of affected animals.
Horses infected with Salmonella Infantum may develop oral ulcers, limb swelling, weight loss, limb lameness, liver disease, and general weakness. The prognosis is poor.
TREATMENT
The major objective in treating diarrhea in the horse (whatever the age) is to restore and maintain fluid and electrolyte balance. In the acute stage this may require administration of large volumes of fluids intravenously over 12 to 24 hours or longer. Plasma transfusions may even be indicated in very severe cases. If the animal's condition stabilizes, further fluids can be given orally by stomach tube or by allowing access to water containing electrolyte solutions (fresh water must be available). Normal fecal consistency will be restored most often without using other medications including antidiarrheal agents. Foals with septicemia usually receive a course of IV antibiotics.
PREVENTION
Salmonellosis is a highly infectious disease, and the build-up of contamination in the environment of the infected horse can place other animals at risk. Ideally, suspected or confirmed cases should be isolated, and strict sanitation measures observed (bleach is the most effective surface disinfectant). Many serotypes of Salmonella Typhimurium are pathogenic for humans. Salmonella Typhimurium definitive type 104 (DT104) has emerged as a common cause of salmonellosis in humans and cattle, yet previous reports involving horses are sparse.
The most effective prevention involves good management practices to reduce stressful situations and sanitation. Horses with the history of exposure to antimicrobial drugs prior to hospitalization and abdominal surgery during hospitalization are associated with Salmonella shedding in adult horses with gastrointestinal tract disease. Foals with gastrointestinal tract disease are more likely to shed Salmonella organisms than are adult horses with gastrointestinal tract disease. Risk of Salmonella infections is greater for horses with large colon impactions.
References:
1. Myonecrosis and cutaneous infarction associated with Salmonella serovar Infantum infection in a horse.Pellegrini-Masini A, Dolente BA, Habecker PL, Jesty SA. (pubmed.gov)
2. Veterinary Notes for Horse Owners, captain M. Horace Hayes
3. Risk factors associated with fecal Salmonella shedding among hospitalized horses with signs of gastrointestinal tract disease.Ernst NS, Hernandez JA, MacKay RJ, Brown MP, Gaskin JM, Nguyen AD, Giguere S, Colahan PT, Troedsson MR, Haines GR, Addison IR, Miller BJ. (pubmed.gov)
4. Emergence of Salmonella typhimurium definitive type 104 (DT104) as an important cause of salmonellosis in horses in Ontario.Weese JS, Baird JD, Poppe C, Archambault M. (pubmed.gov)
5. Risk factors for nosocomial Salmonella infection among hospitalized horses.House JK, Mainar-Jaime RC, Smith BP, House AM, Kamiya DY. (pubmed.gov)