Pigeon fever, also called dryland distemper, develops when Corynebacterium pseudotuberculosis bacteria enter a horse’s body, probably via insect bites or breaks in the skin. The infection, which usually causes abscesses in the chest or elsewhere in the horse’s body, was once thought to be limited to California and the Southwest but but is now found in other regions, including Kentucky, Wyoming, Utah and Colorado.Most horses make a full recovery, but it can take weeks for the disease to run its course.
Currently, there is no vaccine available against pigeon fever. “A protective vaccine is one of my career goals,” says Sharon J. Spier, DVM, PhD, DACVIM, of the University of California–Davis. “There is research in progress, and some products are still undergoing safety testing. We are definitely getting closer to a safe vaccine, but we don’t have one yet.”
For now, the most effective way to protect your horse against pigeon fever is with protective management. Here are five measures that can help reduce your horse’s chances of developing the disease:
1. Keep up with fly control. Fly sheets and repellents can help protect horses, but measures to reduce the flies breeding on your farm—such as parasitic wasps and feed-through products called insect growth regulators (IGRs)—are also important. “A fly-control program should be started early enough in the season to prevent a large buildup of flies,” says Spier. “Whenever temperatures get up around 70 degrees is when you need to start using these products. If there are cattle on your place, you need to control horn flies because they feed along the underside of the horse. This may cause ventral midline dermatitis, which can open the way for pigeon fever bacteria.”
2. Pick up manure from paddocks. The bacterium that causes pigeon fever, Corynebacterium pseudotuberculosis, thrives in manure-laden soil. Picking up manure daily or using feed-through IGRs will help reduce the population.
3. Keep wounds clean and protected. Check your horse daily for scrapes and sores, and treat any you find with a disinfecting wound cleaner. After the wound is clean, applying a layer of antibiotic ointment will help keep flies away from the exposed tissues. Bandaging, when possible, might also be beneficial.
4. Quarantine newcomers to the farm. Horses may harbor a pigeon fever infection for three to four weeks before showing signs. When you bring new horses onto your property, it’s a good idea to keep them isolated from resident horses long enough to be sure they are not carrying any infectious diseases.
5. Practice good biosecurity. Maintaining the habits of good hygiene will go a long way toward protecting all of the animals on your farm from illness. “The same principles apply for any infectious diseases,” says Ben Buchanan, DVM, DACVIM: “washing your hands, not sharing water buckets, not dunking the hose in the water bucket, keeping the stalls clean and the flies down.”