What is Salmonella/salmonellosis?
Salmonella is a gram negative bacteria that can affect both foals and adults.
There are several strains of Salmonella that affect horses. The most common is S. typhimurium.
How does Salmonella affect horses?
Salmonellosis (the disease caused by Salmonella) can cause a variety of problems.
Many horses can have Salmonella in their body, but don’t shed it and often aren’t ill. Some horses shed Salmonella without showing signs of illness (asymptomatic shedders). This is why it can be a difficult disease to contain. Stress, caused by things like transporting, foaling, moving to a new stable, overcrowding, illness or surgery, can compromise their immune system making them susceptible to signs of disease.
In foals it can cause gastrointestinal issues but often develops into life threatening septicaemia.
In adult horses, the bacteria are more likely to be confined to the GI tract, particularly the colon. On some occasions it can also cause abortion, but not often. It is much rarer in mature horses for bacteria to get out of the GI tract and into the bloodstream.
How do horses get Salmonella?
There are a range of ways that horses can contract salmonella:
- Salmonella is faecal-orally spread between animals. Normal adult horses rarely eat manure, but mares and foals often eat one another’s faeces. Salmonellosis is therefore more common in breeding environments.
- Foals do eat manure and can pick it up that way. They may also pick it up inadvertently by nuzzling a mares flank that has been on dirty bedding
- Horses may also get infected by eating grass, hay or other feed contaminated with manure containing Salmonella.
- Contaminated boots, water buckets, tack, grooming tools and unwashed hands can transfer bacteria from an infected horse to a healthy one.
- Rodents (rats and mice) can carry Salmonella and spread infected droppings to horse feed within a stable or farm.
Diagnosing Salmonella in horses
Diagnosis is based on clinical signs, culturing faecal samples or via PCR testing. The difficulty with faecal samples is that Salmonella can shed intermittently so a negative faecal culture will not necessarily mean the horse is free of Salmonella. PCR tests have been used to identify Salmonella DNA, but a PCR positive test does not mean the organism is alive. The test can identify DNA from dead organisms, which might mislead you into thinking the horse is still infective.
Symptoms of Salmonella in horses
If a horse’s immune system is compromised when it is exposed to Salmonella, it is at higher risk of disease.
Salmonella in foals
In foals, the first signs are bloating soon after birth with possible lameness and joint swelling. Once septicaemia sets in the foal becomes dull and depressed with a high fever and can die within 48 hours
Salmonella in adult horses
In adult horses, acute enteritis is the most common sign, with fever and severe diarrhea. The watery diarrhoea has a rotten smell and often contains mucus, and sometimes blood. Severe dehydration and toxaemia occur. The animal can go off its food and become very weak.
How to prevent horses getting salmonellosis
Farm hygiene and biosecurity
Prevention involves good farm hygiene practices to remove faeces and clean the environment – clean stalls and stables with an alkaline detergent (better for organic matter/faeces) and disinfect with a high quality disinfectant.
Ensure people wash hands and use foot baths after each time an animal is handled. In some circumstances (equine hospital) it may be better to use latex gloves when handling a horse and wear a new pair every time an animal is handled.
Overcrowding can put stress on the animal and therefore increase shedding by a horse that’s carrying Salmonella. If there is an outbreak, overcrowding increases the rate of spread. It is best to keep the horses in smaller groups on the farm and separated in an equine hospital.
Quarantine/isolate sick animals or animals that have diarrhoea where possible.
Have a good rodent prevention plan. Mice droppings in hay or grain can be a significant source of Salmonella
If a horse gets salmonellosis, other horses should be closely monitored
Treatment for horses with Salmonella
The most important treatment is to rehydrate the animal. Salmonella causing watery diarrhoea dehydrates the animal very quickly
Fluid is usually given intravenously to foals, and even to adult horses because the gut is often too compromised to absorb fluids given orally.
Antibiotics (in some cases)
Antibiotics are controversial in treating Salmonella. One concern that has recently surfaced in veterinary and human medicine is the number of Salmonella isolates that have developed multiple antibiotic resistance patterns, making them hard to treat with antibiotics
Antibiotics are given to foals with documented or suspected infection because the organism more often will get beyond the GI tract and into the bloodstream.
Antibiotics are sometimes given to adult horses with documented infection to prevent the organism spreading beyond the GI tract.
Probiotics are becoming more popular in cases of diarrhoea to ensure the microbiome is re-balanced helping to optimise the immune system and often preventing the need for antibiotic use.
Strategic anti-inflammatory treatments
With any cause of diarrhea, there is always a risk that the horse might develop laminitis, so anti-inflammatory treatment is often instituted.
Most horses infected with Salmonella clear the organism from the body within days or weeks, but some may not be clear from infection until months later.
Can people get Salmonella from horses?
People can and do become infected with salmonella from horses. Ingesting contaminated faeces causes Salmonella in people.
Clinical signs in humans are similar to adult horses ie. diarrhea, abdominal cramps and fever.
It is important to practice good hygiene to prevent catching Salmonellosis. Always wash your hands before eating and don’t touch objects with manure-contaminated hands.
Salmonella bacteria can cause illness and even death in foals and adults. The disease is easily spread, and difficult to control and eradicate. However, good general hygiene and management techniques can help prevent problems in your horses.
Zamira is an Australian animal health company with a mission to improve the health, wellbeing and productivity of animals across the world. Read more about us here.