Q: My horses live at home, and I haul in for lessons with a trainer. There are unconfirmed rumors that a barn where I take riding lessons recently had a case of pigeon fever. Is my horse at risk of catching it if I take him to the barn for lessons, or could we bring it home and expose my other horses? —Erin, Texas
A: I appreciate your concern about your horse contracting Corynebacterium pseudotuberculosis, the bacterium that causes pigeon fever. Fortunately, I believe there are some measures you can take to decrease the chance of transmission to your horse or other horses at your barn.
The bacteria are able to survive for long periods in soil (eight months or more), and transmission occurs by flies or through direct contact with contaminated soil or with pus from the disease’s characteristic abscesses. Many insects have been incriminated as vectors for transmitting the disease to horses, and study results have shown that Haematobia irritans (horn flies), Musca domestica (house flies), and Stomoxys calcitrans (stable flies) can act as mechanical vectors of this disease.
Where these abscesses appear on the body suggests that ventral midline dermatitis (open sores near the girth region caused by biting flies) is a predisposing cause of infection. Disease incidence fluctuates considerably from year to year, presumably due to herd immunity and environmental factors such rainfall and temperature. It is also seasonal, with the highest number of cases occurring during the dry months of the year, which are summer and fall in the southwestern United States, although cases may be seen all year. This disease can now be found in all regions of the country and has been reported in Mexico and Western Canada.
Biosecurity practices to limit the spread of C. pseudotuberculosis are aimed at reducing environmental contamination and spread via insects or fomites (transfer via inanimate objects). The bacterium is endemic (here to stay) in many regions of the world and is particularly able to survive in soil that’s contaminated with manure.
Horse owners and farm managers on properties with C. pseudotuberculosis should use commonsense biosecurity measures to limit the spread to other horses:
- Wear disposable examination gloves when working with infected horses, followed by hand-washing;
- Isolate affected horses from naive (never had the disease) herdmates;
- Protect horses from insect exposure by applying insect repellents to the horse regularly, including to the ventral midline to prevent ventral midline dermatitis; and
- Practice meticulous wound care (e.g., topical fly repellents, antimicrobial ointments, and bandages) to prevent infection from a contaminated environment.
In your particular situation, when you trailer in for lessons, keep your horse away from any infected horses. Apply fly repellent to your horse before you leave your farm and again after your lesson. Clean your horse’s manure out of your trailer so as not to attract flies that you can take back to your barn. Wash your hands frequently, use your own buckets from home, and clean out your trailer again when you return to your barn.
There is currently a commercial vaccine in the United States for controlling C. pseudotuberculosis in horses that is manufactured by Boehringer-Ingelheim and available through veterinary distributors. Vaccination and a comprehensive fly control program (e.g., insect growth regulators, spray repellents, fly parasites, adult traps, and manure removal) are recommended for disease prevention.