Rebecca S. McConnico, DVM, PhD
What is pigeon fever?
Pigeon fever is the common term for an infection caused by the bacterial organism Corynebacterium pseudotuberculosis. C. pseudotuberculosis bacteria tend to localize and form abscesses in the pectoral region and ventral abdomen of the horse. It is a common misconception that the condition is related to pigeons. It was named because the abscesses cause swelling and give the horse's chest a "pigeon-breast" appearance. It is also known as dry-land strangles. Cross-species transmission is rare and usually only occurs between horses and cattle because they can carry the same strain. The bacterium is responsible for many different types of diseases in many different animals, and it can rarely infect humans.
How did my horse get pigeon fever?
The organisms tend to live and multiply in dry soil and manure. Hot, dry weather is the most common environment where the organism is found, and most pigeon fever cases appear in late summer/early fall. The drought conditions in our state and surrounding states likely caused the increase in equine cases this year. Horses contract the disease through open wounds or fly bites. A horse's immune system competence can dictate whether he contracts pigeon fever.
This disease has traditionally occurred more frequently in horses in California, although recent outbreaks have been reported in Connecticut and other states. The Louisiana Animal Disease Diagnostic Laboratory reports at least 11 positive cases in Louisiana horses this year. There are likely many other cases that may have gone undetected since it is not commonly seen in this part of the U.S.
What are the signs of pigeon fever?
In the horse there are three recognized forms of the disease: external abscesses, internal abscesses and ulcerative lymphangitis. The first sign you might see is swelling of the chest or abdomen, which might lead to the hose being sore at the walk. There may be general or localized swellings, fluid accumulation under the skin, dermatitis, lameness, and draining abscesses or tracts. The horse might have a fever but usually exhibits a normal attitude and appetite, or becomes lethargic. A small percentage of horses can develop internal abscesses, which are more serious and carry a more guarded prognosis. The most common site for horses to get internal abscesses is the liver, but they have also occurred on the kidneys, lungs and spleen. The infection can spread to the horse's legs, causing a syndrome called ulcerative lymphangitis, which can be difficult to treat. It usually manifests by painful inflammation, nodules and ulcers, especially in the region of the fetlock; occasionally the entire limb can swell. The discharge is odorless, thick, greenish white and blood tinged. Usually, only one leg is involved. Horses with ulcerative lymphangitis may suffer from some degree of permanent swelling or chronic lameness.
How will my veterinarian diagnose pigeon fever?
A veterinarian can suspect pigeon fever from clinical signs but can reach a definitive diagnosis through bacterial culture. They may also run blood work to b sure the horse doesn't have a systemic infection.
How do you treat pigeon fever?
Treatment usually consists of surgically opening the abscesses to allow drainage by a licensed veterinarian. THe abscesses can be lanced as soon as they are mature. Applying warm compresses to abscesses can help bring the abscesses to a head. Your veterinarian can also ultrasound the abscesses and find the best place for drainage. The abscesses should be cleaned and flushed daily with a dilute betadine solution. As long as the horse is healthy and has a normal appetite and attitude, your veterinarian may not choose to administer antibiotics. Many clinicians believe that antibiotics will delay the maturation of developing abscesses and lead to internal abscessation. If the abscesses are deep and causing pain and discomfort to the horse, nonsteroidal anti-inflammatory medications such as phenylbutazone, flunixen meglumine or firocoxib (Equioxx) can be administered. General supportive and nursing care is indicated. If treatment is successful, the swelling gradually recedes over days or weeks.
What should I do to protect my other horses?
There is no vaccination for pigeon fever. Affected horses should be isolated because drainage from their abscesses contains a high amount of bacteria that will contaminate the environment. Flies are a major vector and can spread the bacteria, so spray affected and unaffected horses (especially ones with open wounds) with fly repellent. A good feed-through fly control product is also an option. People can carry the bacteria on their shoes, hands, etc., so be sure to maintain good hygiene after handling your sick horse. This includes washing your hands after touching each horse, wearing gloves when treating sick horses, and changing your clothes and shoes between sick and healthy horses. Bedding, water buckets and any other materials that come in contact with pus should be disinfected or disposed of and not shared with other horses. Bleach and other disinfectants do not work well on organic debris (dirt or manure), so pouring disinfectants on the ground is not effective. Bleach does work well on clean surfaces, like stall mats and scrubbed walls.
For additional information, contact your local veterinarian or the LSU School of Veterinary Medicine at 225-578-9500.