There has been an unusual rise in cases of pigeon fever detected in Colorado and Wyoming, according to recent reports from Colorado State University (CSU) and the Wyoming State Veterinary Lab.

Seventy-six cases from Colorado’s Front Range (the area immediately east of the Rockies) have been confirmed by the CSU Veterinary Diagnostic Laboratory since early fall, more than six times the number of cases from last year’s total of 12. In Laramie, Wyoming, an area that typically only has a few cases per year, there have been 110 cases of pigeon fever reported by a single veterinarian.

Pigeon fever is one of the most commonly diagnosed bacterial problems in California (and several other western states). This disease is caused by Corynebacterium pseudotuberculosis and is seen worldwide. It usually is associated with very deep abscesses and multiple sores along the chest (hence the name pigeon fever, as the chest swells up and resembles a large pigeon breast). Occasionally there will be sores on the midline and abdomen, or even in aberrant places such as the back. The bacteria can cause an ulcerative lymphangitis (which causes the hind legs to swell and “bust out” in crusts). Horses also can suffer from internal abscessation. The causative bacteria live in the soil and can enter the horse’s body through wounds or broken skin, and through mucous membranes. It can be transmitted by various flies, including house flies and probably horn flies. See article #3946 for more information on the symptoms associated with pigeon fever and accompanying photographs.

Donal O’Toole, MVB, director of the Wyoming State Veterinary Laboratory said that “Historically, (pigeon fever) has been called dryland distemper, and it is seen in the fall and is reportedly carried by flies. We’ve had hard frosts and several snowstorms, that should have killed off any fly activity, yet we’ve continued to see cases long after fly seaso