Equine Pigeon Fever | Local News | fairfieldsuntimes.com - Fairfield Sun Times

Jenn Swanson

Agriculture/4-H Agent

Teton County-MSU Extension Office

We're all familiar with the proud, puffy-chested pigeon, strutting his stuff on barns and cathedrals alike. Is he a building wrecker or a park bench pet? Well, folks could squab-ble about that, but there's at least one thing for which the perky bird is clearly blameless and that's pigeon fever.

Pigeon fever cropped up in Montana equines this year, surprising local veterinarians who have rarely or never seen this disease across decades of practice. Ironically, pigeon fever has nothing to do with birds. On the contrary, flying insects and a soil bacterium called Corynebacterium pseudotuberculosis are the culprits. Infected horses commonly develop large abscesses on the chest, causing a look reminiscent of the puffed-up breast of a pigeon. And now you know the rest of the story!

Different variants of C. pseudotuberculosis infect horses (biovar equi) and sheep (biovar ovis), but both variants can infect cattle. Equine outbreaks start when flying insects deliver a dose of bacteria to broken skin or mucous membranes. Equine infections typically follow 1 of 3 routes, each involving abscess formation. The first is abscessation under the skin but external to the body cavities, which is the most common. The second is abscessation inside body organs or cavities, occurring in 8% of cases. The third and least common is abscessation in the lymph nodes of the legs, called ulcerative lymphangitis. The likelihood of a full recovery is high for healthy horses with external abscesses, whereas the prognosis is a lot less rosy for the other two forms.

Other common names for equine pigeon fever are "dryland distemper", reflecting its propensity to crop up in arid regions, and "false strangles" because both pigeon fever and equine strangles are associated with abscesses. (Unlike pigeon fever, however, equine strangles is a respiratory tract infection caused by the bacterium Streptococcus equi.)

Diagnosis: Pigeon fever is often diagnosed clinically (based on signs and symptoms); a definitive diagnosis requires identifying the bacterium in pus or an antibody-based blood test.

Treatment: External abscesses may spontaneously rupture and, if not, should be properly drained and flushed when well-encapsulated. Post-lancing, the wound benefits from topical care to make sure it keeps draining and doesn't get secondarily infected. Internal abscesses and ulcerative lymphangitis require ongoing antibiotics and other veterinary care. A 30% to 40% mortality rate has been reported in horses with internal abscessation.

Prevention: Fly control to prevent soil-to-horse and pus-to-horse transmission is helpful. Manure removal may be helpful. A horse vaccine is conditionally approved, but efficacy is not well established. Sheep and goat vaccines are approved. (The disease is known as caseous lymphadenitis in small ruminants.)

Why now? No one knows for sure, but Montana's outbreak could be drought related.

How many? Dr. Tahnee Szymanski, the assistant state veterinarian for Montana, says she's heard anecdotally of 50 to 100 cases across multiple counties. But an informal poll of local veterinarians yielded that same number of presumptive cases in Teton County alone, so the actual statewide number may be much higher.

Are new cases declining now that it's cold?  New equine cases continue to show up Teton County this week despite the declining numbers of flies (the disease incubation period is 1 to 4 weeks, up to several months). At least one bovine infection was recently reported in this area.  Stay tuned for more on ovine and bovine infections with C. pseudotuberculosis.

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