When Corynebacterium pseudotuberculosis bacteria enter a horse’s body, usually via insect bites or breaks in the skin, the infection can take three different forms. Here are the treatments for each form of pigeon fever:

External abscesses—Horses with external pigeon fever abscesses usually don’t need systemic antibiotics, but they sometimes receive anti-inflammatory medications to relieve pain and swelling. Swellings that do not interfere with breathing, swallowing or movement are often left to mature and drain on their own. In some cases, however, a veterinarian may determine that it’s best to lance an abscess once it is mature—that is, the body has fully encapsulated the infection. To speed maturation process, hot compresses may be applied to the affected area. After abscesses are drained, daily flushing of the wound will help promote healing.

Internal abscesses—Ultrasound imaging may be used to locate and evaluate internal pigeon fever abscesses as well as to guide efforts to aspirate the infected mass for culturing. Several common antibiotics are effective against C. pseudotuberculosis, but the location and nature of the abscesses may pose treatment challenges in individual cases. In addition to oral antibiotics, intramuscular or intravenous administration may be required. Long-term antimicrobial therapy—lasting from one to four months—is often necessary to treat internal pigeon fever abscesses.

Ulcerative lymphangitis—Intravenous and oral antibiotics and anti-inflammatories are generally administered until the lameness and swelling subside. Thereafter, the horse is usually given oral antibiotics to prevent relapse. Other treatments may include iodine scrubs, hot packs and poultices. “A single drug may not be enough to combat this type of infection,” says Hector Gonzalez, DVM, of Bakersfield Veterinary Hospital in California. “Those cases are difficult and need prolonged treatment, and sometimes combinations of antibiotics.”