Equestrian Network Magazine

Pigeon Fever

"Pigeon Fever" is a disease about which horse owners in Central California should be aware.Pigeons have nothing to do with the disease other than that the disease can cause a pronounced swelling on the horse's chest that resembles a pigeon.Other names for the disease include "Dryland Distemper", "Pigeon Breast Fever", "Dryland Strangles", and Corynebacterium Pseudotuberculosis.

This disease is caused by a bacteria that can survive for long periods of time in the soil. It is thought to be transmitted to horses by flies feeding on abrasions or small wounds already present. The flies can plant the bacteria which then penetrate and proliferate in these warm, moist environments. Although also seen throughout the southern United States, California is particularly well known for having a high incidence of this disease, especially during the late summer and early fall. The more arid parts of our state are heavier hit by Pigeon Fever. Like so many other diseases, there are some years in which the prevalence seems to be much higher than others.

The typical signs include abscesses anywhere along the ventral midline including the chest, sheath/mammary glands, or in small chains along the lymphatic channel of a leg. Large plaques of ventral edema are also frequently present adjacent to the abscesses (ventral

edema causes sponge-like swelling on the underbelly of horses). Rarely, it can cause an internal abscess as well (less than 3% of all cases). Fever, weight loss, depression and lameness are also frequently present in some combination with internal and external abscesses. Pigeon Fever abscesses usually take several weeks to mature, but occasionally can cause long-lasting infections over a year in duration.

Pigeon Fever should be considered at the top of the list in any horse that has an abscess in a typical location. The diagnosis can be confirmed by culturing fluid taken from an abscess and identifying the bacteria, but often the diagnosis is presumptive. If a positive culture is not obtained or if your veterinarian suspects an internal abscess, there is also a blood test that can be performed to help diagnose the disease. This blood test is performed at the University of California at Davis and is very affordable.

Draining the abscess is the mainstay of treatment but should not be performed until the abscess is mature.

Treatment of the disease may vary depending on the severity of infection and on which body systems are involved. Draining the abscess is the mainstay of treatment but should not be performed until the abscess is mature. If done prematurely, the abscess is more likely to recur. Abscess maturity can be determined by palpation (they generally get soft in the middle when they are mature) and by ultrasound. Ultrasound is also helpful to determine if there are multiple pockets of fluid and to identify deep abscesses. Once opened, the abscess cavity should be flushed daily with an antiseptic solution such as betadyne or nolvasan.

Most horses will be completely over the disease within 3 weeks of draining the abscess. Once the abscess matures and the condition resolves, over 90% of horses will remain immune to the disease in the future.In those rare instances where the disease recurs, it is unknown whether recurrence is due to re-infection or relapse of the original disease. Horses that have difficulty clearing the infection should be evaluated for possible causes of immune suppression (such as Equine Cushings Disease). Horses affected with external abscesses have an excellent prognosis, but internal abscesses can be more devastating and are fatal in 40% of cases.

Antibiotic usage is controversial. Many veterinarians advise against administering antibiotics for external abscesses because of the potential to delay abscess maturation. However, in cases involving internal abscesses or involving the lymph channels of a leg ("Lymphangitis"), long-term antibiotics are generally prescribed.

Prevention is centered on good sanitation practices and fly control. Quarantine of affected individuals is not generally necessary because the insects carrying the bacteria can travel long distances anyway. Practicing good fly control can help reduce other diseases as well. At our hospital we use a spray system and "fly predators" as well as daily manure evacuation to accomplish this. In a barn setting, daily feeding of a small scoop of a new product called "Solitude IGR" made by Pfizer is thought to dramatically reduce fly populations. Research is currently focused on creating a vaccine against this disease.

Tim G. Eastman DVM, DACVS, MPVM was raised in Monterey County California where his family had deep roots in the local horse industry. Like many veterinarians, he decided to become an equine veterinarian at a very young age. He obtained a degree in Animal Science at Cal Poly San Luis Obispo and a business minor. He also obtained a doctorate in Veterinary Medicine from the University of California at Davis in 1996' as well as a Master's Degree in Preventative Veterinary Medicine. He performed a one year internship at Littleton Large Animal Clinic in Littleton Colorado and then a 3 year surgical residency at Texas A&M University in College Station Texas. He met his wife, Alexandra (Alex) in veterinary school and got married during his surgical residency. They now work together as co-owners of Steinbeck Country Equine Clinic in Salinas California.