The continuing drought in the southern parts of the United States seems to have increased the incidence of a disease in horses called pigeon fever. This is not too surprising since the bacteria that causes the disease, Corynebacterium pseudotuberculosis, survives best under hot and dry conditions. The Louisiana Department of Agriculture and Forestry recently announced that at least 100 cases of pigeon fever were reported in that state in 2011, with more than 30 of those cases occurring late in the year.
As a veterinarian, I haven’t treated many horses for this, but when I lived and practiced in rural Wyoming I did a bit of relief work for a mixed-animal practitioner. One day I got a call from a local breeder of Clydesdales who also happened to work part-time for the vet I was “subbing” for. One of her prized fillies was sick. "Would you mind coming out to take a look?" she asked.
After warning her about my relative lack of expertise, I told her I’d be happy to give her my two cents worth. I arrived at her farm, walked up to this huge, gorgeous filly, and immediately thought, "Oh, S%&#." She had a dull look in her eyes, her head was hanging, and her pectoral (chest) muscles were hugely swollen. I took her temperature. If I remember correctly, it was in the range of 104 (normal for horses is around 100 give or take a degree or so). Her heart was racing, her breathing heavy, and her gums were dry and muddy in color. I was in way over my head, but I thought I knew what was going on … pigeon fever.
I performed a little triage, and the owner quickly loaded the filly onto a trailer as I called the "real" horse vet, the one who had an equine hospital one valley over, to let him know what was headed his way. He confirmed the diagnosis, but, unfortunately, the filly died the next day despite his excellent care.
Horses infected with Corynebacterium pseudotuberculosis typically develop abscesses in the chest area, giving them a pigeon breast appearance. This explains the disease’s name, but an abscess can form almost anywhere in the body. My patient’s case was more severe than normal. I suspect that she also had internal abscesses that complicated her treatment. Horses that have only external abscesses tend to recover uneventfully once they (the abscesses) have rupture or are lanced and drain. Antibiotics are usually reserved for those cases where internal involvement is suspected, since they don’t seem to positively affect the course of the disease otherwise.
The biggest issue with pigeon fever is how contagious the disease can be. When an abscess drains, the bacteria that are released can be spread to other horses via flies, people’s hands, shoes, clothing, etc., or through contact with pus in the environment. Horses with external wounds are at especially high risk. A preventative vaccine for pigeon fever is not available.
If you ever suspect that your horse has pigeon fever, isolate him or her and call your veterinarian. Lancing, draining and flushing the abscess allows the infected pus to be collected and discarded, which limits the chances that the disease will spread. Contaminated equipment should be thrown out or cleaned with soap and water, and then disinfected with bleach to remove organic material.
Dr. Jennifer Coates