Widespread Pigeon Fever Reported in Oregon

Veterinarians in Oregon are reporting a surge in cases of Corynebacterium pseudotuberculosis (also known as pigeon fever or dryland distemper), a bacterial disease that can linger in a horse for months. Jessica Evans, DVM, of Bend Equine Medical Center in Bend, Ore., said vets at the clinic have seen an average of three new cases every day since mid-August.

When it infects Corynebacterium pseudotuberculosis localizes in deep abscesses in the breast (pectoral) muscles, along the abdomen, and/or in the groin (sheath or udder) region. The pigeon fever name comes from swelling of the chest that resembles a pigeon's breast. Pigeons have nothing to do with causing or spreading the disease.

Corynebacterial organisms can live in the soil at all times, but they become most pathogenic during drought conditions. Dryland distemper is thought to be transmitted through the bacterium's contact with abrasions, insect bites, wounds, or mucous membranes. Since these infections appear to peak during the autumn months when flies are particularly abundant, veterinarians say it is probable that flies serve as vectors to carry organisms to the skin.

Evans said the first case the practice saw was a horse at a busy boarding facility.

"Ever since then, the number of cases increased exponentially," Evans said. "We see it at the big places and the small places. Unfortunately, when there is a high-density horse population, such as at a boarding facility, we can see a lot of cases because the flies are spreading it so rapidly."

Draining pigeon fever abscess

The abscess pockets created by pigeon fever a loaded with thick, creamy pus, as much as a quart at a time. A scalpel incision is used to open the capsule to drain the abscess. A container should be held beneath the opening to collect as much of the infectious drainage as possible for removal from the premises.

Pigeon fever is difficult to manage, as it's transmitted so easily and can linger in the horse's system, undetected, for months.

Evans said some horses get as many as 30 abscesses over the course of their infection, while others have one or two, from which they recover quickly. Resolution of the disease "depends on the horse," she said. "Recovery rate has to do with the individual horse's immune system and how aggressively they are treated."

Fly control is the primary focus of pigeon fever prevention. Evans recommends that horse owners in the affected region use fly sprays, sheets, and masks, to prevent insect bites. Horse owners can also utilize feed-through fly control treatments to decrease the overall number of insects on their property. Owners should wrap or cover any open wounds on their horses covered, or at least apply fly-deterring chemicals around the injury

There is no reliable vaccine for horses.

Evans said that while horse owners should not be dissuaded from participating in area equine activities, they should avoid taking their horses to facilities with known active outbreaks. Beyond that, "unfortunately there's really not too much we can do," she said.

Treatment of pigeon fever can require patience and persistence. Hot packing of the swollen area can help bring the abscess to a head, improve circulation, resolve edema, and make the horse more comfortable. If recommended by the treating veterinarian, owners can also give a low dose of a non-steroidal anti-inflammatory (NSAID) medication to alleviate discomfort. Then it's a matter of time until the abscesses are ready to finally "point," mature, and will feel soft to the touch.

"When the abscesses are mature we recommend surgical lancing," Evans said. "Some people prefer to wait and let them rupture on their own, but we believe surgical lancing allows for better drainage and quicker resolution. Once opened, we have owners flush the abscess with a dilute Betadine solution, and do that daily until the wound heals."

Most veterinarians prefer not to use systemic antibiotics in horses with superficial abscesses, as they can cause the infection to simmer along at a low level, only to reappear once the antibiotic course comes to an end.

Recovery can take weeks or months. Nancy S. Loving, DVM, reported in "Pigeon Fever: Abscesses Within and Without" that 91% of infected horses recover with no subsequent relapse or reinfection; these individuals might develop a long-lasting immunity. It is possible for infection to travel to internal organs, such as the liver, kidneys, or heart. It can also cause ulcerative lymphangitis in some cases. In these cases intensive care might be required.

Those treating infected horses are also reminded to utilize good hygiene practices, including handwashing and footbaths. As the bacteria can be spread by flies within a certain radius (depending on how far the flies travel), isolating infected horses won't provide complete protection, but it can be helpful from a management perspective.

"People should remember to be clean and not carry the bacteria to other horses," Evans said.

While pigeon fever used to be considered primarily a "California disease," reports across the arid western states have increased in the past few years. In 2002 Kentucky veterinarians reported cases. Whether this is due to hot, dry weather or increasing interstate transport of horses is anyone's guess.

Read more about pigeon fever incidence and forms of infection, treatment, and control.

About the Author

Erin Ryder

Erin Ryder is a former news editor of The Horse: Your Guide To Equine Health Care.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from TheHorse.com. Learn More