Signs of a contagious animal disease called pigeon fever have been found in dozens of horses in Eastern Oregon this fall [2007].

Despite the name, the disease is not spread by the bird. Rather, the bacterial infection can cause abscesses that lead a horse's chest to swell like a pigeon's.

Dr. Fred Robinson of Riverside Veterinary Clinic in Pendleton said he has seen an increasing number of cases this fall [2007], just as he did in 2005.

"There were 80 or so horses treated then, and at this point, with the season not over, we're approaching 50 horses."

Dr. Jason Down of the Hermiston Veterinary Clinic said he's only seen 4 potential cases this year [2007], but he noted that Idaho veterinarians are noticing an up tick.

"This is the time of year that you see it, early fall, late fall," he said. "It's endemic in California. It's really common to that area."

Though pigeon fever gets it name from the swelling in the chest, the disease can cause swelling anywhere on the horse's body. The animal feels pain when touched on a swollen area, so owners and caretakers must look for the swelling, because horses don't give any other clues.

"They don't usually go off their feed, and the horse's attitude doesn't change," Robinson said.

Down said a veterinarian can confirm the infection only with a bacterial culture. The infection is contagious among horses, so owners should isolate infected animals. Down said it's important to drain the abscess so it doesn't infect other horses then clean up well.

"People don't get it, but they can carry it among horses on their clothing, boots, tools," he said.

The bacteria live in the soil and enter the animals' skin through routine abrasions. The incubation period can run from a few days to several weeks, and it's generally not fatal.

[ProMed Mail Moderator's comments - Pigeon fever, pigeon breast, breastbone fever, dryland distemper, dryland strangles, false strangles, false distemper are the names that this disease -- caused by the bacterium _Corynebacterium
pseudotuberculosis_ -- are most frequently known by. Geographically, it was at one time considered to be a disease of California, where it is regarded as endemic. However, it is much more widespread now, especially in the western states of the US, but it has a worldwide distribution. It is a seasonal disease, usually appearing in late fall but can appear sporadically at any time of year.
The signs of pigeon fever can also initially resemble those of other diseases such as strangles. Sometimes the only initial signs are lameness and a reluctance to move. It can strike a horse of any age, sex or breed, but usually attacks young adult animals. There is a low incidence in foals.

It has also been diagnosed in cattle, and a similar disease affects sheep and goats. The disease is not transmissible to humans, although humans can carry the infectious agent on shoes, clothing, hands or barn tools and transfer it to another animal.

Clinical signs include lameness, fever, lethargy and weight loss and usually is accompanied by very deep abscesses and multiple sores along the chest, midline and groin area and, sometimes, the back. Abscesses also can develop internally.
The disease is called pigeon fever because infected animals often develop abscesses in their pectoral muscles, which swell and resemble a pigeon's chest. Although the disease is considered seasonal, with most cases occurring in early fall, a number of cases have been confirmed during winter months and other times of the year as well.

The causative bacteria live in the soil and can enter the animal's body through wounds, broken skin or through mucous membranes. Additionally, some researchers believe pigeon fever may be transmitted by flies.

Of the types of disease (external abscesses, internal abscesses or limb infection [ulcerative lymphangitis]), the ulcerative lymphangitis is the most common form worldwide and rarely involves more than one leg at a time. Usually, multiple small, draining sores develop above the fetlock.

The most common form of the disease in the United States is external abscessation, which often forms deep in the muscles and can be very large. Usually, it appears in the pectoral region, the ventral abdomen and the groin area. After spontaneous rupture, or lancing, the wound will exude liquid, light tan-colored, malodorous pus.

Internal abscesses can occur and are very difficult to treat. The most common forms are external abscess and lymphangitis, with the prognosis of a full recovery being generally good. Internal abscesses are much more difficult to treat.

The contagious nature of the disease means an accurate diagnosis is imperative, and treatment should be initiated as well as control of insects and the rigid practice of biosecurity.

Horse owners should be aware of the clinical signs and understand veterinary care must be timely. Infected horses should be isolated, the abscesses properly treated and the drainage properly disposed of. The area where the infected horse is kept must be properly cleaned and completely disinfected, because this is a very hardy bacterium. Bacteria in the pus draining from abscesses on infected horses can survive from one to 55 days in the environment. They have also been shown to survive from one to 8 days on surface contaminants and from 7 to 55 days within feces, hay, straw or wood shavings. Lower temperatures prolong the survival time.
Pest control is extremely important. The bacteria may be transported between animals by flies. Flies are also being investigated in the role of instigator of this disease.

Horses may become infected but not develop abscesses for weeks. The disease usually manifests in younger horses but can occur in any age, sex, and breed.

A different biotype of the organism is responsible for a chronic contagious disease of sheep and goats, _Caseous lymphadenitis_, or CL. Either biotype can occur in cattle.

Treatment in horses often consists of hot packs or poultices applied to abscesses to encourage opening. Open abscesses should be drained and regularly flushed with saline. Surgical or deep lancing may be required, depending on the depth of the abscess or the thickness of the capsule, and should be done by your veterinarian. Ultrasound can aid in locating deep abscesses so that drainage can be accomplished. External abscesses can be cleaned with a 0.1 percent povidone-iodine solution. Antiseptic-soaked gauze may be packed into the open wound. A nonsteroidal anti-inflammatory drug, such as phenylbutazone, can be used to control swelling and pain.
Antibiotics are controversial. Their use in these cases has sometimes been associated with chronic abscessation and, if inadequately used, may contribute to abscesses, according to one study. The most commonly used antibiotic for the treatment of this condition is procaine penicillin G, administered intramuscularly, or trimethoprim-sulfa. In the case of internal abscesses, prolonged penicillin therapy is necessary.

Buckets or other containers should be used to collect pus from draining abscesses, and this infectious material should be disposed of properly. Consistent and careful disposal of infected bedding, hay, straw or other material used in the stall is vitally important. Thoroughly clean and disinfect stalls, paddocks, all utensils and tack. Pest control for insects is also very important.
With treatment, animals usually recover between 2 weeks to 77 days. Although some animals may have recurrences, generally recovery is complete, and the prognosis is good.

Portions of this comment have been extracted from:
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