Pigeon fever — named for the chest swelling that gives affected horses a pigeon-breast appearance — is caused by Corynebacterium pseudotuberculosis. Originally a disease of the arid western US, reports have increased in frequency and geographic range. Huber et al. (J Vet Intern Med 2016) confirmed temperature, drought conditions, and fly season length as the strongest predictors of outbreak intensity in California.
Three Forms
External abscesses (approximately 75%): large, firm, warm swellings on the chest, ventral midline, or hindlimbs. Abscesses grow over days to weeks, eventually softening and rupturing. Affected horses are febrile (39 to 40 degrees C) and depressed during active development.
Internal abscesses (approximately 8 to 10%): form in liver, spleen, or lungs. Horses present with weight loss, fever of unknown origin, and internal pain without external swellings. Guarded to poor prognosis.
Ulcerative lymphangitis: recurring ulcerative nodules along lower limb lymphatics with marked swelling. Risk of permanent lymphatic damage.
Treatment: External Abscesses
Primary treatment is drainage, not antibiotics. Antibiotics withheld because (1) thick capsule limits penetration, (2) premature use impairs maturation.
- Monitor daily for maturation: softening, fluctuance, and visible point
- Hot pack twice daily for 20 to 30 minutes
- Surgical drainage when mature; ensure complete evacuation
- Lavage with dilute chlorhexidine or povidone-iodine; avoid hydrogen peroxide
- Maintain dependent drainage; Penrose drain if needed
- NSAIDs for pain and fever
Most external abscesses resolve within 3 to 6 weeks. Horses are not immune after infection. Antibiotics (penicillin or trimethoprim-sulfonamide) indicated for internal disease or ulcerative lymphangitis.
Biosecurity
Isolate affected horse. Dispose of drainage material; do not compost. Disinfect with bleach (1:32) or quaternary ammonium compounds. Implement insect control. No commercial vaccine available in the US.
Sources: Huber L et al. J Vet Intern Med 2016; Pringle JK et al. in Equine Infectious Diseases, 2nd ed. (2014).