Oregon Sees Rise in Pigeon Fever Cases Among Horses

On October 9, the Oregon Department of Agriculture noted a recent uptick in infections. Reports from the Equine Disease Communication Center indicate confirmed cases in Crook and Deschutes counties, with suspected cases also noted in Deschutes County.

Pigeon fever is caused by Corynebacterium pseudotuberculosis, a bacterium that can infect horses, cattle, and other animal species. While the current situation predominantly involves horses, the disease's relevance extends to mixed-animal practitioners, as cattle can also contract infections.

The disease, which derives its name from the swelling that can occur in a horse's chest, presents primarily as external abscesses in the pectoral muscles and abdomen. It can also lead to internal abscesses or ulcerative lymphangitis, which involves the lymphatic vessels and may result in severe swelling and lameness. Common clinical signs include fever, lethargy, decreased appetite, painful swellings, and draining abscesses. Internal infections may be harder to identify due to the lack of visible external lesions.

Corynebacterium pseudotuberculosis is persistent in the environment, capable of entering through skin breaks. Flies, particularly horn flies, can transmit the bacteria, and contaminated materials may further facilitate the spread. The disease tends to peak in occurrence during late summer and fall.

Historically, pigeon fever has also affected cattle in North America. In 2002 and 2003, an increase in C. pseudotuberculosis infections was reported across several U.S. states including Colorado, Kentucky, Utah, and California. Investigators identified related strains among horses, cattle, and sheep, determining a connection between the cases. In cattle, the infection can cause skin abscesses and can link to issues such as mastitis and internal abscesses, which can lead to reduced milk production in dairy herds.

Veterinarians are encouraged to recognize suspicious lesions in both horses and cattle, confirming diagnoses through bacterial culture or PCR tests. They should reinforce fly control measures and maintain biosecurity by isolating infected animals and properly handling any contaminated materials. All suspected cases must be reported to the ODA Disease Reporting Hotline at 503-986-4711. Treatment can vary based on the severity and location of the infection.

The priority remains the identification of additional equine cases and preventing environmental contamination. The potential impact on local cattle health in light of the rising equine cases is yet to be determined.