IN FOCUS: PIGEON FEVER
History: Also called dryland distemper or Colorado strangles, pigeon fever was first reported in the San Francisco Bay Area in 1915. For much of the 20th century it was almost exclusively found in the Southwest and California. About 20 years ago, however, pigeon fever began appearing in other regions. Outbreaks have since been reported in Kentucky, Wyoming, Utah, Oregon, Idaho and the panhandle of Florida. The increase in hot, dry conditions related to climate change is thought to be contributing to the spread of the disease. Cause: Pigeon fever develops when Corynebacterium pseudotuberculosis bacteria enter a horse’s body via insect bites or breaks in the skin. On farms where the disease has been identified, up to 20 percent of flies may carry the bacteria. Signs: swollen chest and midline, due to abscesses forming in the muscles near the surface in those areas. This gives the horse the “pigeon-breasted” look. Affected horses may not develop a fever. For the small percentage who develop internal abscesses, signs take longer to become apparent and may include coughing, lethargy, decreased appetite and/or weight loss. Diagnosis: Laboratory testing is crucial to diagnosis. Samples can be taken from abscesses near the surface and cultured for C. pseudotuberculosis. When abscesses are internal, bloodwork will be done to look for signs of inflammation as well as antibodies to the responsible bacteria. These results, along with ultrasound images and clinical signs, lead to the diagnosis. Treatment: When possible, abscesses are surgically opened and drained. The resulting wounds are kept clean and antibiotics may be prescribed. Antibiotics are used to treat internal abscesses, and other medications may be administered to control potential complications related to the affected location. Prognosis: Most horses recover fully, but it may take weeks for the disease to run its course. Horses with internal abscesses have a guarded prognosis.