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 manifested as a variety of clinical signs. These include 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 anesthesia, surgery, antibiotic or deworming medications, change in feed, management, or weaning. These events may cause changes in food intake, and bowel movements. The development of the disease depends on the immune status of the horse, the type of bacteria involved, and the presence of external factors.
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.
Horses infected with Salmonella Infantum may develop oral ulcers, limb swelling, weight loss, limb lameness, liver disease, and general weakness. The prognosis is poor.
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 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. Ffresh 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.
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. Bbleach is the most effective surface disinfectant. Many serotypes of Salmonella typhimurium are pathogenic for humans. 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 are associated with Salmonella shedding. 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.