It's funny how diseases get their names. Take "pigeon fever," for example. Most folks wouldn't get too concerned if they found out that local pigeons were running a fever, but tell an equestrian that his horse or mule has pigeon fever, and it's a whole nother story.

Horse and mule owners who have never heard of pigeon fever before will cock their heads and raise their eyebrows as they try to figure out what their veterinarian just said. Those who are familiar with the disease are justifiably concerned.

What is Pigeon Fever?Pigeon fever is the common name for an infection caused by the bacteria Corynebacterium pseudotuberculosis (also known as Dryland Distemper). Based on the name of the infection, it would be easy to assume that pigeons played an integral role in the transmission of disease. In reality, pigeon fever got its name because the bacteria commonly cause abscesses and dramatic swelling in the equine's chest, giving the horse or mule the appearance of having a "pigeon-breast."

Where is Pigeon Fever Found?Historically, pigeon fever cases have been most commonly found in California. However, over the last several years, veterinarians have diagnosed cases throughout the western United States, including eastern Oregon. Unfortunately, the climate of Eastern Oregon is perfect for C. pseudotuberculosis. Unlike many bacterial pathogens, C. pseudotuberculosis tends to live and multiply best in dry soil and manure and is most prevalent in drought years.

Clinical SignsThe first sign that horse and mule owners typically notice is that the chest or abdomen of their equine is swollen. It is not unusual to immediately think that the swelling is the result of being kicked or some other traumatic injury. As the chest continues to swell (the abscess continues to develop) horses and mules might show signs of lameness and or be unwilling to walk as much as they normally would. Even though the name suggests that animals affected with pigeon fever will have elevated temperatures, most horses and mules will not run a fever, and their attitude and appetite remain normal. In addition to local swelling, horses and mules may show considerable edema (fluid swelling) along the belly and/or between the front legs. Abscesses may also localize in the udder of mares or the sheath of males.

Occasionally equids develop internal abscesses - which have a set of concerns all of their own. Internal abscesses can adversely affect internal organs. Horses and mules with internal abscesses have a guarded prognosis. A syndrome known as "ulcerative lymphangitis" can develop if the infection spreads to the horses' legs. Ulcerative lymphangitis can be painful for the affected animal and difficult to treat.

TreatmentUnfortunately, there is no silver bullet elixir for the treatment of pigeon fever. Management of uncomplicated cases focuses primarily on helping the abscesses development via the use of hot packs and poultices. These abscesses may take months to develop to the point where they can be effectively lanced and drained. When your veterinarian feels the abscess has developed sufficiently he will make a surgical incision that will allow the abscess to drain. When your veterinarian lances the abscess there is typically a large volume of thick, creamy pus, which will flow freely through the incision. Catch as much of the purulent material as possible to remove from the premises.

The use of antibiotics is controversial. Most veterinarians agree that unless there are complications such as internal abscesses, ulcerative lymphangitis or the animal is severely depressed, it is better not to use antibiotics. Horses that are placed on antibiotics may actually experience a protracted course of disease. Horses that are sore or seem uncomfortable may be helped by the administration of medications like banamine or bute.

ControlSince C. pseudotuberculosis persist in the soil, it is impossible to completely eliminate the bacteria and risk of exposure, the cornerstone of control is through exposure reducing management practices. The best approach to prevention and control rely on basic hygienic practices:

? Isolate affected horses - particularly if there is an abscess that is actively draining;

? All contaminated tack, tools, equipment and stalls should be disinfected;

? People may also serve as vectors to transmit bacteria from horse to horse. All sick animals should be fed and handled after healthy animals have been tended to. Hands and cloths should be washed thoroughly after handling sick animals;

? Insects should be controlled ; and

? Preventive herd health strategies (such as vaccination, deworming, dental care, and good dietary management) should be utilized to maintain strong immune systems to help ward off infection.

Dr. Jerald Rice owns and operates Enterprise Animal Hospital on Depot Street.

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