Pigeon Fever is the common term for an infection caused by the bacterial organism Corynebacterium pseudotuberculosis (also referred to as Dryland Distemper). C. pseudotuberculosis bacteria tend to localize and form abscesses in the pectoral region and ventral abdomen of the horse. It is common misconception that the condition is related to pigeons. It was named because the abscesses cause swelling and give the horse’s chest a “pigeon-breast” appearance. Ruminants-such as sheep, goats, and cattle-can also become infected with these bacteria, although cross-species transmission is rare and usually only occurs between horses and cattle because they can carry the same strain.
Pigeon fever cases used to be found primarily in California, although within the last several years veterinarians have diagnosed cases in many areas of the western United States. The organisms tend to live and multiply in dry soil and manure. Hot, dry weather is the most common environment where the organism is found, and most pigeon fever cases appear in late summer/early fall (the author first diagnosed a case in August, and her number of cases has increased exponentially since that time). Horses contract this disease through open wounds or fly bites, and sometimes through their mucous membranes. Some horses have developed lung abscesses after inhaling a concentration of bacterial organisms. A horse’s immune system competence can dictate whether he contracts pigeon fever.
The first sign owners usually notice is swelling of the chest or abdomen. The horse might have a fever (temperature grater then 101.5 F), but he usually exhibits a normal attitude and appetite. An affected animal might be sore at the walk, usually after swelling and abscess of his chest and abdomen have occurred. Some develop more severe infections where they acquire multiple abscesses and become systemically ill (inappetent, febrile, and lethargic). A small percentage of horses can develop internal abscesses, which are more serious. The infection can spread to the horse’s legs, causing a syndrome called ulcerative lymphangitis, which can be difficult to treat.
A veterinarian can reach a definitive diagnosis through bacterial culture, although clinical signs can be quite diagnostic. If the horse is systemically ill, it is helpful to run blood work to be sure he doesn’t have overwhelming systemic infection and to monitor internal organ function. If the horses develop internal abscesses, their disease is more serious and carries a guarded prognosis.
Treating pigeon fever consists mainly of surgically opening the abscesses to allow drainage. The abscesses can be lanced as soon as they are mature, Applying warm compresses to abscesses can help bring them to a head. Your veterinarian can also ultrasound the abscesses and find the best place to drain them. The abscesses should be cleaned and flushed daily with dilute Betadine soulution. The use of systemic antibiotics is controversial. Many clinicians believe that antibiotics will delay the maturation of developing abscesses and might facilitate internal abscessation. As long as the horse appears healthy and has a normal attitude and appetite, this author prefers to withhold antibiotic therapy. If the abscesses are deep and causing pain and discomfort to the horse, Banamine (flunixin meglumine) can be administered.
Prevention and Control
As in the case of all infectious disease outbreaks, our goal is to limit the number of horses affected. Affected horses should be isolated because drainage from their abscesses contains a high amount of bacteria that will contaminate the environment. Flies are a major vector and can spread the bacteria, so spray affected and unaffected horses (especially ones with open wounds) with fly repellent if it is still fly season. A good feed-through fly control product is a good option. People can carry the bacteria on their shoes, hands, etc., so be sure to maintain good hygiene after handling your sick horse. Bedding, water buckets, and any other materials that come in contact with pus should be disinfected/disposed of and not shared with other horses.
By Jessie Evans, DVM