Salmonella

Also Know As

Salmonellosis, Septicemic salmonellosis

Description

Salmonella is the most commonly diagnosed infectious cause of diarrhea in horses. It is an infection of the intestinal tract by a bacterial pathogen called Salmonella, named after the pathologist Daniel Elmer Salmon who recognized Salmonella as a major cause of diarrhea in livestock. Symptoms are caused by toxins produced by the Salmonella species bacteria.

In the mild form, and in the early stages of infection, there may be little or no diarrhea, but fever is prominent in most cases. At this stage, there may be some mild colic signs. Fever and mild colic should suggest that Salmonella may be the cause of the horse's illness.

In more severe cases, the diarrhea is watery, profuse, projectile, and malodorous. The horse is very uncomfortable, and tail switching, straining, and periodic rectal prolapsing may occur. The horse shows colicky symptoms by lying down and getting up repetitively in an attempt to find a comfortable position.

In the most severe cases, bloat, colic, flatulence, and even bloody diarrhea are prevalent. When a horse reaches this stage, Salmonella has usually caused considerable damage to the large and small intestine.

Young foals may also develop diarrhea associated with infection by Salmonella bacteria. Certainly, Salmonella infection should be considered as a possible cause in any foal presenting with diarrhea. Salmonella in young foals appears to have a relatively unfavorable prognosis.

In many cases, the Salmonella bacteria invade the body of foals and cause septicemia, which occurs when bacteria disseminates through the bloodstream to different parts of the body. Common locations for Salmonella bacterial spread in foals include the joints, with lameness attributable to septic arthritis, and the lungs, where pneumonia may develop.

There are over 100 different strains of Salmonella. Some are much more likely to cause diarrhea than others. Horses normally carry at least one species of Salmonella in their intestinal system, and some horses carry several. As normal residents of the intestine,the Salmonella bacteria do not cause harm, in fact, they contribute to digestion.

Salmonella bacteria normally present in the horse's intestine are prevented from becoming too prevalent by other resident bacteria that constitute the normal flora or microbiota in the horse's digestive system.

In addition, the horse's immune system plays a critical role in keeping Salmonella bacteria at bay, and the horse's normal bowel movements stir up the bacteria and keep them moving along so they do not gain a foothold on the bowel wall.

Symptoms

  • Fever
  • Dehydration
  • Diarrhea: may be severe and bloody
  • Colicky behavior
  • Depression
  • Discoloration of gums
  • Gas-caused abdominal distention
  • Bone and joint infections
  • Loss of appetite

Causes

Salmonella is caused by a bacterial pathogen called Salmonella, with symptoms caused by the toxins produced by the bacteria. Rodents commonly act as a source of infection on farms where the disease is endemic.

Many horses may be carriers. In adults, most cases of Salmonella develop after the stress of surgery or transport, especially when horses are moved through sales yards, deprived of feed and water, and then overfed at their destination. Mares may be inapparent shedders and, despite several negative cultures before foaling, may shed the bacteria at parturition and infect the newborn foal.

Salmonella in horses hospitalized for other causes is a major problem for equine clinics and stud farms. In these circumstances, carriers are constantly reintroduced, the environment is persistently contaminated, and a large population of vulnerable horses is at risk. Septicemic Salmonella is also common in foals; it may be endemic or there may be outbreaks.

Prevention

Healthy horses are at a much lower risk of infection than those whose immune systems are compromised in some way, so minimizing stress and illness is an important method of preventing problems. A horse that has normal digestive tract function, and therefore a healthy and balanced population of gut microflora, is also less susceptible.

Medications including antibiotics or non-steroidal anti-inflammatory drugs that challenge the environment or integrity of the gut can provide an opportunity for infection. These medications should be used as directed by a veterinarian and not given indiscriminately.

Preventing the spread of Salmonella from other horses:

  • Disinfect shoes and equipment when returning from a show or event where other horses are present
  • Do not allow horses to eat off the ground at a show, trail ride, or other event
  • Isolate new horses for several weeks before allowing them to have contact with other horses
  • Because veterinary hospitals care for so many sick horses, it is not unusual for a clinic to harbor Salmonella bacteria, often the antibiotic-resistant strains, despite stringent control measures. Owners should monitor a horse returning from a stay at a veterinary clinic for signs of disease.

Preventing the spread of Salmonella while caring for an affected horse in your barn:

  • Isolate the sick horse, caring for it after other horses have been handled
  • Disinfect boots, hands, and equipment such as rakes and wheelbarrows as soon as they leave the sick horse’s stall
  • Use care in disposing of manure and bedding from stalls of infected animals. Don’t spread this material on fields where other horses are turned out. Composting will eventually kill the bacteria.
  • Keep barn animals (cats, dogs, goats) away from the affected horse, and attempt to seal the stall against mice and other barn pests.
  • Anything touched by a sick horse must be cleaned to prevent the spread of disease. This includes trailers, tack, buckets, tools, grooming implements, stall, and the horse’s handler (hands, boots, clothing, and so on). Check with a veterinarian for disinfection guidelines. This can be a complicated process, but is extremely important to prevent the spread of disease.
  • Although an affected horse seems to have recovered from a Salmonella infection, it may shed bacteria in its manure for several weeks. Some hospitals require at least five days of negative cultures before a horse is pronounced free of disease. Be sure the horse is completely healthy before it is allowed contact with other horses.

Every effort must be made to prevent introduction of a carrier; animals should be purchased directly only from farms known to be free of the disease and should be isolated for at least a week while their health status is monitored. Ensuring that feed supplies are free of salmonella depends on the integrity of the source.

Treatment

After a veterinarian has confirmed that a horse has contracted Salmonella, the treatment will vary, ranging from no treatment to intensive medical care in a referral hospital. Treatment may include intravenous fluid therapy for shock and to replace fluid losses from diarrhea, antibiotics to support the horse's system while its immune system responds, non-steroidal anti-inflammatory drugs such as banamine to reduce signs of shock, and plasma to provide protein, replace fluid losses in the diarrhea, and to reduce signs of shock.

The major objective in treating diarrhea in the horse 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. 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.

In many horses, illness caused by Salmonella runs its course in five to seven days. After this period, the horse slowly recovers, although it may take several weeks before manure consistency returns to normal. In these cases, supportive care may include administration of electrolytes and fluids, as severe diarrhea can quickly lead to dehydration.

Pain medications and anti-inflammatories are sometimes given to keep the horse comfortable.

Antibiotic therapy is rarely the first treatment choice. Antibiotics are not very effective against some strains of Salmonella and their use may deplete populations of helpful bacteria.

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