Common names: pigeon fever, pigeon breast, breastbone fever, dryland distemper, dryland strangles, false strangles, false distemper.
Geographic incidence: Endemic to California, but now found in most western states in the United States.
Seasonal: Usually appears in late fall but can appear sporadically at any time of year.
Cause: Corynebacterium pseudotuberculosis.
Vaccine: None at this time.
Reservoirs and mode of transmission:
* Can live in the soil and enter the horse’s body through wounds or broken skin and through mucous membranes.
* May possibly be transmitted by flies, including the common housefly and horn flies.
* Disease is usually highly contagious and can easily infect multiple horses on the premises.
* Bacterium in the pus draining from abscesses on infected horses can survive from 1 to 55 days in the environment. It has also been shown to survive from 1 to 8 days on surface contaminants and from 7 to 55 days within feces, hay, straw, or wood shavings.
* Lower temperatures prolong the survival time.
Clinical signs:
* Early signs can include lameness, fever, lethargy, depression, and weight loss.
* Infections can range from mild, small, localized abscesses to a severe disease with multiple massive abscesses containing liters of liquid, tan-colored pus.
* Deep external abscesses, swelling, and multiple sores develop along the chest, midline and groin area, and, occasionally, on the back.
Incubation period: Horses may become infected but not develop abscesses for weeks.
Animals affected:
* The disease usually manifests in younger horses, but can occur in any age, sex, and breed.
* A different biotype of the organism is responsible for a chronic contagious disease of sheep and goats, Caseous lymphadenitis, or CL. Either biotype can occur in cattle.
Disease forms:
* Generally three types: external abscesses, internal abscesses, or limb infection (ulcerative lymphangitis).
* The ulcerative lymphangitis is the most common form worldwide and rarely involves more than one leg at a time. Usually, multiple small draining sores develop above the fetlock.
* The most common form of the disease in the United States is external abscesses, which often form deep in the muscles and can be very large. Usually these abscesses appear in the pectoral region, the ventral abdomen, and the groin area. After spontaneous rupture, or lancing, the wound will exude liquid, light tan-colored, malodorous pus.
* Internal abscesses can occur and are very difficult to treat.
Diagnosis: Your veterinarian can easily collect a sample for culture at a diagnostic laboratory. It is important to isolate the bacterium to get a definitive diagnosis since pigeon fever can superficially resemble other diseases.
* Hot packs or poultices should be applied to abscesses to encourage them to open. Open abscesses should be drained and regularly flushed with saline.
* Surgical or deep lancing may be required, depending on the depth of the abscess or the thickness of the capsule, and should be done by your veterinarian.
* Ultrasound can aid in locating deep abscesses so that drainage can be accomplished.
* External abscesses can be cleaned with a 0.1 percent povidone-iodine solution.
* Antiseptic-soaked gauze may be packed into the open wound.
* A nonsteroidal anti-inflammatory drug such as phenylbutazone can be used to control swelling and pain.
* Antibiotics are controversial. Their use in these cases has sometimes been associated with chronic abscessation and, if inadequately used, may contribute to abscesses, according to one study.
* The most commonly used antibiotic for the treatment of this condition is procaine penicillin G, administered intramuscularly, or trimethoprim-sulfa.
* In the case of internal abscesses, prolonged penicillin therapy is necessary.
Care required:
* Buckets or other containers should be used to collect pus from draining abscesses, and this infectious material should be disposed of properly.
* Consistent and careful disposal of infected bedding, hay, straw, or other material used in the stall is vitally important.
* Thoroughly clean and disinfect stalls, paddocks, all utensils, and tack.
* Pest control for insects is also very important.
Recovery time: Usually anywhere from 14 to 77 days.
Prognosis: Usually good with complete recovery, although some horses may experience recurrence.