Introduction/Causative Agents: Fistulous withers is a condition found in horses where the supraspinous bursa (located near the withers) becomes inflamed. This condition can be caused by traumatic injuries or infectious agents. When an infectious agent is involved it is most often caused by Brucella abortus. When an infection of Brucella abortus occurs, this condition is sometimes called brucellosis.
Clinical Signs: At first, the most common signs are swelling, heat, and pain in the withers area. This can come on suddenly or appear over some time. If the problem is severe, the horse may have a fever, be lethargic, and have stiffness throughout the body. With time the bursa may rupture and have a straw colored or infectious looking discharge. This can heal over, leaving a scab or it can keep draining for many days. If left untreated, the problem can heal and then show up again some time later. In almost all cases, the area surrounding the bursa becomes thickened with scar tissue and inflammation. Occasionally, if Brucella abortus is the cause, abortions can occur.
Disease Transmission: If Brucella abortus is suspected as the cause for the fistulous withers, the horse most likely obtained the disease from cattle infected with Brucella. Studies indicate that horses that are pastured or have a close association with cattle are more prone to developing the problem. Some studies also show that horses infected with Brucella abortus where the bursa is open and draining can spread the disease to cattle. Studies indicate that in cattle infections can occur by consuming contaminated feed and water. The organisms also may enter the body through mucous membranes, conjunctivae (lining and surface of the eye), wounds, and in some cases, intact skin.
Diagnosis: Cultures of a sample taken from an unruptured bursa, or blood tests looking for titers to Brucella can identify infected animals.
Treatment: If the bursa is unruptured and not draining, treatment with antibiotics and anti-inflammatory agents is recommended. When the bursa is fistulated or draining, most treatments include removing any involved tissues and flushing the area with dilute betadine or other solutions. Antibiotics are also often given to help prevent additional infections.
Prevention: Presently, the best prevention option is to keep horses away from potentially infected cattle. It would also be recommended that cattle be separated from horses that have fistulus withers where any drainage is occurring.
Public Health Concerns: Materials contaminated with B. abortus are hazardous to humans and should be handled carefully.