At least nine horses have been confirmed with pigeon fever in central and eastern Oregon this year, according to the Oregon Veterinary Medical Association. Additional confirmed and suspected cases were reported in October, prompting state officials to urge veterinarians and horse owners to strengthen disease recognition and biosecurity.
The Oregon Department of Agriculture (ODA) warned on Oct. 9 that cases had increased in recent months. Subsequent reports from the Equine Disease Communication Center included confirmed cases in Crook and Deschutes counties, along with suspected cases in Deschutes County.
Pigeon fever is caused by Corynebacterium pseudotuberculosis, a bacterium that can infect horses, cattle and other animal species. Although the current Oregon reports involve horses, the disease is relevant to mixed-animal practitioners because cattle can develop their own forms of infection.
What is Pigeon Fever?
Pigeon fever is named for the prominent swelling that can develop in a horse’s chest, resembling a pigeon’s breast. The most common form causes external abscesses, particularly in the pectoral muscles and along the underside of the abdomen. The disease can also cause internal abscesses or ulcerative lymphangitis, an infection involving the lymphatic vessels that can produce severe limb swelling and lameness.
Clinical signs may include fever, lethargy, reduced appetite, painful swelling and draining abscesses. Internal infections can be more difficult to identify as horses may lack obvious external lesions.
The bacterium lives in the environment and can enter through breaks in the skin. Flies, particularly horn flies, can mechanically transmit the organism. Contaminated equipment, bedding and other materials can also contribute to spread.
Pigeon fever is often seasonal, with cases increasing during late summer and fall. Environmental persistence makes management challenging, particularly when abscesses drain and contaminate soil or bedding.
A History of Pigeon Fever in North American Cattle
Pigeon fever may be best known as a disease of horses, but cattle have also been affected in North America. In 2002 and 2003, veterinarians reported a rise in C. pseudotuberculosis infections across several U.S. states, including Colorado, Kentucky, Utah and California.
The increase prompted researchers to investigate whether the cases were connected. They identified related bacterial strains among horses, cattle and a sheep. The investigation included four bovine cases and found evidence of an expanding epidemic in Utah, although the increases reported in other states involved multiple strains.
In cattle, the infection can cause skin abscesses, ulcerative lymphangitis and, in some cases, mastitis or internal abscesses. Dairy-herd outbreaks documented in other countries have also resulted in reduced milk production and culling.
These reports show that cattle are susceptible to the same bacterium responsible for pigeon fever in horses. Whether the current increase in Oregon equine cases has any implications for cattle in the region remains unknown.
What Should Veterinarians and Producers Do?
Recognize suspicious lesions. In horses, examine the chest, underside of the abdomen and limbs for painful swelling, abscesses or draining lesions. In cattle, consider C. pseudotuberculosis when investigating unusual skin lesions, abscesses, lymphangitis or compatible mastitis cases. Bacterial culture or PCR can help confirm the diagnosis.
Strengthen fly control and biosecurity. Use appropriate fly-control measures, maintain wound hygiene and clean up manure to reduce fly populations. Isolate infected horses, particularly those with draining abscesses. Wear gloves when handling lesions, contain purulent material and clean contaminated equipment and surfaces. Do not share buckets, grooming tools or other equipment between infected and healthy animals without appropriate cleaning and disinfection.
Report suspected cases. Pigeon fever is immediately reportable in Oregon. Veterinarians must contact the ODA Disease Reporting Hotline at 503-986-4711 when the disease is suspected. Follow state guidance on isolation, quarantine, diagnostic sampling and treatment.
Treatment depends on the location and severity of infection. External abscesses may require drainage and flushing, while internal infections and ulcerative lymphangitis can require more intensive veterinary management.
The immediate priority is identifying additional equine cases and limiting environmental contamination. Whether the current increase in Oregon equine cases has any corresponding impact on cattle remains unknown. Diagnostic laboratory findings and further information from state animal health officials could help clarify whether the current activity has implications for bovine health.
