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Pigeon Fever


2012/01/01


By Jennifer Dunlap, DVM

You may have heard through the “horsey grapevine” there has been a rise of Pigeon Fever cases in many states, including TN, that formerly had no or few cases of Pigeon Fever. The disease used to be seen strictly out west. People may be fearful of this disease and, of course, no one wants their horses to become ill. There is often misinformation passed through the internet, so here are the facts about the disease. The good news is that even for the most severe cases, those with internal abscesses, there is now an antibiotic regimen that has been used successfully to treat those affected horses.

The Disease:

I) Definition: Pigeon fever is also known as Dryland Distemper, False Strangles and Breastbone fever. Pigeons have nothing to do with the disease! It is called “pigeon fever” because the swelling from the abscesses in the chest give a “pigeon breast” appearance to the horse's chest. The name “false strangles” comes from the fact that it forms draining abscesses and can form internal abscesses just like strangles.

II) Cause: It is caused by the bacteria Corynebacterium Pseudotuberculosis. This bacteria is hardy and can survive on surfaces for a week and in dirt and bedding for up to 55 days. Lower temperatures tend to prolong survival of the bacteria.

III) Three forms:
1. The most common and most easily healed: external abscesses. 90% of these form in the chest; the rest form on the underside of the abdomen and, rarely, on the hind end in the hip area.
2. Much less common: internal abscesses. These carry a small risk of fatality, but there are antibiotic treatment regimens that are EXTREMELY effective at treating this form of the disease.
3. Ulcerative lymphangitis - by far the most painful. It is localized in the legs and causes severe swelling, multiple draining abscesses and non-weight bearing lameness.   

IV) Signs:
1. The primary complaint (in cases I've seen) is stiffness when walking, lasting for 2-3 days before the swelling starts to develop into a large lump. 
2. Painful swelling in chest, then drainage.
3. Fever, sometimes as high as 104.
4. Being off feed, feeling depressed, hanging head.
5. Limb swelling

V) Contagion:
1. Horses can contract the disease through open wounds, mucous membranes and, possibly, fly bites. The pus is the infectious agent. 
2. VERY RARELY the disease can be passed between species, with a miniscule risk of human infection, especially in immunocompromised people. 

VI) Treatment:
1. Antibiotics (usually a combination of doxycycline and rifampin) are used ONLY in complicated cases, such as with a horse that is systemically ill, i.e., feeling bad, off feed, severely lame due to leg swelling and abscesses or has internal abscesses. Uncomplicated cases of pigeon fever are typically not treated with antibiotics because there is the risk that the antibiotics could drive the infection into the abdominal lymph nodes, leading to severe complications. 
2. Keeping a horse isolated in a stall until a month after the abscesses have stopped draining. At that time, the stall should be stripped with bedding completely removed as well as the top layer of dirt, and the stall cleaned then disinfected with bleach. Keeping an affected horse in a stall will limit the amount of cleaning that has to be done and will minimize the environmental size of the contamination. Because the bacteria can live in the dirt, it is a lot of work and trouble to pull the dirt out of an entire paddock or pen. Clean up there would be like a hazardous materials clean-up.
3. Caretakers should wear gloves, boots used only for that stall, use separate forks and manure buckets, with a separate area for manure disposal away from communal manure piles. Wash hands frequently!
4. Banamine or Phenylbutazone (bute) to help control fever.
5. Hot pack affected areas to encourage drainage.
6. Lance abscesses surgically if drainage does not occur spontaneously.

The majority of horses recover uneventfully, although those who develop complications with leg swelling or severe abscess formation in the chest can have permanently thickened tissue. Monitor your horses carefully for a stiff gait, chest swelling, fever and depression, going off feed, or unexplained abscesses on neck and body. Let your veterinarian know immediately if you suspect your horse might be showing signs of this disease.

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