Pigeon Fever in Horses.

Michelle, a tech at Lewiston Veterinary Clinic, called and suggested that I write an article about "pigeon fever" in horses. They've been seeing as many as 4 or 5 cases per day. I also talked to Dr. Egland at Lewiston Veterinary Clinic, and Dr. Rustebakke from Rustebakke Veterinary Services in Clarkston, and found a summary article on the Internet from the Colorado State University Veterinary Teaching Hospital, to gather information for this column.

Pigeon fever most commonly causes deep infections and abscesses in the chest and lower neck. (It has nothing to do with pigeons, except that the swollen chest makes the horse look like a pigeon.) It is also sometimes called pigeon breast (not to be confused with the congenital condition in humans that causes an abnormally shaped chest), breastbone fever (though it has nothing to do with the breastbone), false strangles, dryland strangles, and dryland distemper. (And by now you won't be surprised to learn that strangles and distemper are lay terms for a streptococcal infection in horses that has nothing to do with pigeon fever). Pigeon fever can cause a fever. In the early stages, the only other symptoms may be lethargy and an arthritis-like lameness.

The disease is caused by a bacteria ("corynebacteria"), which can also cause similar diseases in sheep, goats and cattle, but not humans. I could find no evidence of it causing disease in dogs although we have been trying to cure an unusual swelling on a dog's neck for a few weeks now. The same bacteria can cause deeper internal abscesses, and draining infections in the legs of horses.

Corynebacteria can live in dirt, bedding, etc, and seems to be commonly spread by biting flies. It can infect open wounds, inflamed skin, and can penetrate mucus membranes, so it could also be spread by contaminated tack, brushes, and feed and water buckets. You could spread it by contact with your hands or gloves. Sanitation is important. The pus that drains from abscesses should be collected, if possible, and disposed of properly. After the initial infection it may take weeks for the swellings to develop, and though the prognosis is good with proper treatment, it may be weeks before the disease is cured. Dr. Egland said they generally don't see new cases in the winter, but based on his experience, they may be treating abscesses into December.

With this and other infections that form abscesses, it may be best to not use antibiotics until the abscess comes to a head, breaks open or can be lanced, and the pus can drain out. Before that happens, antibiotics may not cure the infection, and may only slow down the development of the abscess. Diagnostic ultrasound may be used to check for deep internal abscesses. Other supportive care, like intravenous fluids and medication to control pain and inflammation may be needed. Every case is different and the best treatment will depend on the examination and evaluation of the attending veterinarian, and how the patient responds to treatment as the case progresses.

Dr. Rustebakke was in an equine practice in the central coastal region of California in the mid 1970's where the disease was common then. The first cases he saw here in the Northwest were in 1987, and then there were very few cases until another outbreak in 2003. Last year was not too bad, but this year there is a major outbreak, with more cases from the Camus Prairie, the Palouse, and, according to the University of Colorado, throughout most western states. There's no vaccination, but you can get good veterinary care, and that's important.