Pigeon Fever is a bacterial disease caused by Corynebacterium pseudotuberculosis. Historically, it was believed to be common only in in dry, dusty climates such as the West and Southwest, however it has spread to many regions of North America, including Canada and Mexico.
The reservoir for infection is soil, and the disease is transmitted by flies. Stable flies, house flies and horn flies have been found to carry the bacteria. The bacteria is introduced into the skin, via open wounds or abrasions. Inflammatory cells carry the bacteria deeper into the tissues and to local lymph nodes. The organism is resistant to the body’s defenses because it lives within the inflammatory cells.
Infection causes an abscess surrounded by a severe inflammatory response, resulting in massive swelling in the area of infection.
A small percentage of horses develop internal abscesses (less than 10%), which may manifest as mild to moderate weight loss, fever or other signs depending on which organ is involved. There may be no external signs of swelling and additional laboratory testing is required to diagnose.
Another type of infection with this organism is called Ulcerative lymphangitis, and appears as chains of draining sores on the legs of affected horses.
Abscesses may take weeks to months to develop. The disease can be seen year-round, but more cases are seen in summer, fall and early winter. Abscesses usually develop on the chest, lower abdomen or sheath, but they can occur anywhere on the body. When these abscesses rupture or are surgically opened (lanced) they leak tan, creamy or pus (with no odor) that should be properly collected and discarded, to avoid further contaminating the environment.
A veterinarian should examine affected horses with fever, lameness, depression or decreased appetite, because further tests for internal infection are warranted.
Diagnosis is usually fairly straightforward for abscesses that are near the skin surface. Very deep abscesses may be difficult to find, and require the use of ultrasound. I have had many cases that were chronically very lame. I found the cause to be a very deep abscess in the armpit, triceps, groin or deep muscle of the chest or thigh.
Whether or not the pus is cultured is up to you and your vet. It is a good idea to culture to confirm this disease and monitor for anti-microbial resistance in more complicated cases.
Other Diagnoses Considered
Treatments May Include
Prognosis & Relevant Factors
Generally, the prognosis is good. Abscesses usually slowly come to a head and drain. Once an abscess is opened and drained, the horse feels better quickly. Abscess drainage by a vet can often shorten this process. Occasionally, complications do develop. Even rarer are abscesses within the abdominal and other body cavities.
I Might ObserveRelated Observations
QUESTIONS TO ASK MY VET
Helpful Terms & Topics in HSVGWritten, Reviewed or Shared by Experts in Equine Health
Helpful Outside ResourcesCredible Equine Health Information on the Internet