Pigeon fever is a bacterial disease characterized by the development of single or multiple slow-developing abscesses with creamy white to greenish colored pus. It is caused by infection with Corynebacterium pseudotuberculosis. It manifests in three different presentations in horses, which include:

• Ulcerative lymphangitis: This form of pigeon fever is the most painful to the horse and affects the lymphatic vessels in the hindlimbs. Horses develop multiple small abscesses and ulcers which causes cellulitis, severe lameness and swelling accompanied by loss of appetite, lethargy and fever. One or both hindlimbs might be affected. This form is most frequent in horses living in Texas.
• External abscesses: These develop as large swellings, which occurs most often on the belly or chest (which looks similar to a pigeon breast, hence the name 'pigeon fever'), sheath, mammary gland, or less frequently, the inguinal or axillary regions. These swellings can grow up to 20 cm before they eventually rupture. There is also tissue swelling and sometimes dermatitis along the belly, weight loss, depression and fever. External abscesses are most frequently seen in horses living in the western United States.
• Internal abscesses: This is the most uncommon form of pigeon fever in horses, but when it does occur it is associated with the development of internal abscesses in the horse's lungs, liver and abdominal lymph nodes. It is usually accompanied by weight loss and depression in affected horses.

Transmission
C. pseudotuberculosis is transmitted by flies, dust and soil particles which gain entry into the horse's body through a break in the skin. C. pseudotuberculosis is most abundant in manure-contaminated, sandy and rocky soil. C. pseudotuberculosis is also capable of being transmitted through direct contact with contaminated feed, bedding, fomites or people.

Incubation period
The incubation period is 3 to 4 weeks.