What are Brucellosis?
Brucellosis is a disease caused by several species of Brucella bacterium. It is chronic and contagious. It can affect multiple species of mammals, but is seen particularly in cattle, sheep, goats, bison, pigs, and the horse. Brucellosis is a zoonotic infection, allowing it to spread from animals to humans. The major clinical manifestation of the disease is reproductive failure, such as late abortions, infertility, and severe infections of male reproductive organs. The disease is present in varying degrees in most countries. In many areas, animal disease control programs and occupational safety practices have decreased the impact of the disease over the last 50 years. Much of Australia, Canada, New Zealand, and Western Europe have nearly eradicated brucellosis from their livestock. The United States is nearing eradication, as well. Infection is believed to be spread via fetal membranes and fluids, vaginal discharge, semen, and milk or colostrum. These tissues and fluids can contaminate food and water, spreading the bacteria further.
Brucellosis is an uncommon infection in horses. Two strains of the bacteria, namely Brucella abortus(bovine) and Brucella suis (porcine), are responsible for equine infections. Infection is thought to be caused by direct contact with infected cattle or by ingesting contaminated feed. Although late abortions and sterility in stallions have been recorded in the affected equine population, most horses present with infectious bursitis, tendonitis, and synovitis. Poll evil and fistulous withers are conditions in which aggressive infectious bursitis develops in the tissue and bone of the spinal column. Treatment includes surgical removal of affected tissue, frequent irrigation of bursa, antibiotics and anti-inflammatory agents. There is a high rate of recurrence, and disease often requires several surgeries. Post-operative healing can take as long as 8 months to resolve. Immunizing seropositive horses with Brucella Strain 19 vaccine greatly increases the success rate for resolution of healing.
It is recommended that horses not be pastured or housed with seropositive cattle. Those with active infection should be isolated from other horses. In some countries, Brucellosis is a reportable disease. Seropositive horses may be subject to quarantine or euthanasia.
Brucellosis is a rare bacterial infection caused by Brucella abortus or Brucella suis. The most common abnormality associated with this infection is a suppurative bursitis that affects the connective tissue over the shoulders or poll. Brucellosis can also cause late abortions in affected mares, infertility, and infection of the sexual organs in stallions.
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Symptoms of Brucellosis in Horses
- Affects the top of the horse’s head at the first bone of the neck
- Swelling, warmth, and tenderness will be noted in this area
- Swollen areas will enlarge and burst, creating sinuses that drain pus continuously
- Horse will stand with his head erect and nose poked forward to avoid pain associated with lowering its head
- Affects the withers, the area at the base of the neck above the shoulders
- Severe inflammation, swelling, and pain on manipulation
- One or more pockets draining pus
- Nonspecific lameness due to joint infection
- Late abortions in infected mares
- Body stiffness
- Infection of the reproductive organs of the stallion
- Brucella abortus is responsible for most equine infections, including fistulous withers and most poll evil
- Brucella suis is rare, but can be a cause of poll evil
Causes of Brucellosis in Horses
- Ingesting contaminated feed
- Direct contact with infected cattle
- Spread via fetal membranes and fluids, vaginal discharge, semen, and milk or colostrum
- Tissues and fluids contaminate food and water, spreading the bacteria
Diagnosis of Brucellosis in Horses
Your veterinarian will begin the diagnostic process by conducting laboratory testing. Cultures from semen, blood and milk of symptomatic horses are collected to look for bacteria. Also collected are cultures of fetal tissue, fluids, unruptured bursa, and those from the exudates in cases of fistulous withers and poll evil. Serologic testing searches for titers of the bacteria. Clinical signs, such as stiffness and lethargy, present in your horse during the examination will also indicate the condition.
Treatment of Brucellosis in Horses
Outpatient treatment for your horse will include medication such as antibiotics and anti-inflammatory agents. Inpatient surgical procedures and surgeries may include a local debridement and surgical draining of infected tissue with antimicrobial irrigation, and a radical surgical debridement with or without curettage of the dorsal spinal processes. Repeated surgeries may be needed to adequately treat the infected areas in order to encourage healing and to prevent necrosis.
Recovery of Brucellosis in Horses
There is a high rate of recurrence associated with this disease. Lesions are slow to heal, often taking up to 8 months of combined antibiotic and surgical management. Vaccinating seropositive horses with the Brucella vaccine has greatly improved healing of the lesions.
Prevention of infection in your horse is of upmost importance. Trauma is thought to be a predisposing factor for the development of fistulous withers, so properly fitted saddles and tack should always be used. Horses should not be housed or pastured with seropositive cattle.
Humans can be infected, although transmission rates have declined dramatically in the past 30 years as a result of effective control measures. Brucellosis abortus is a reportable disease in many countries, and seropositive horses may need to be quarantined or subjected to euthanasia.