Pigeon Fever at a Glance
Pigeon Fever Presentation
Comparison
| Presentation | Signs | Treatment | Prognosis |
|---|---|---|---|
| External | Pectoral/ventral abscesses | Hot pack, lance, drain | Excellent — heals in 3–4 weeks |
| Internal | Weight loss, fever, colic | Long-term antibiotics, ultrasound | Guarded — 30% mortality |
| Lymphangitis | Leg swelling, lameness | Anti-inflammatories, ABx | Fair — may cause chronic issues |
| Ulcerative | Trunk/leg ulcers | Wound care, ABx | Good with prompt treatment |
Pigeon Fever Management
Pigeon Fever Control Checklist
| Isolate affected horses immediately | |
| Wear gloves when handling abscess drainage | |
| Disinfect tools and environment after lancing | |
| Use fly control — flies spread the bacteria | |
| Burn or double-bag contaminated bandages | |
| Do not move horses between barns during outbreak | |
| Separate feed and water buckets per horse | |
| Consult vet if no improvement within 48 hours of drainage |
Pigeon fever (Corynebacterium pseudotuberculosis infection) is a bacterial disease of horses characterized by the formation of external abscesses, most commonly on the chest, abdomen, and groin. The name comes from the swollen chest appearance in affected horses, which was thought to resemble a pigeon's breast. The disease is transmitted primarily by flies (horn flies, houseflies, stable flies) and peaks in late summer and fall in the western US, though it has spread to other regions. Most cases are self-limiting with proper abscess management; a minority develop internal abscesses (ulcerative lymphangitis or internal form) with significantly worse prognosis.
| Clinical Form | Frequency | Key Management |
|---|---|---|
| External abscess (chest / abdomen / groin) | ~90% of cases | Hot compress daily; lance only when fully soft and fluctuant |
| Ulcerative lymphangitis (limb) | Uncommon | Prolonged treatment; high recurrence risk in affected limbs |
| Internal abscesses (lung / liver / abdomen) | 8–10% of cases | Months of systemic antibiotics; guarded prognosis |
Epidemiology: Why the West and Why Summer
Corynebacterium pseudotuberculosis is a soil organism that survives in dry, dusty environments. It is endemic in the western US (California, Oregon, Colorado, Texas, Utah) where soil conditions favor its persistence; cases are also increasing in the southeast and mid-Atlantic states as the organism spreads. The primary transmission vector is fly mechanical transmission -- flies that feed on open draining abscesses carry the organism on their mouthparts to other horses. Transmission can also occur through contaminated soil, shared bedding, and wound contamination.
Incidence peaks August through November in California because this is when fly populations are highest following summer and dry conditions concentrate horses near water sources with high fly density. Wet winters followed by dry summers create ideal conditions for both the organism's soil persistence and fly vector activity.
Clinical Forms and Presentation
External abscess form (most common, approximately 90% of cases): Single or multiple firm, painful swellings develop over the pectoral muscles (chest), ventral abdomen, groin, and axillary regions (armpits). The swellings enlarge over 1-4 weeks, then soften as the abscess matures. Affected horses may show: mild fever (101-102 degrees F); reluctance to move (chest abscesses cause discomfort with forelimb movement); weight loss in prolonged cases; depression. Most horses continue to eat and drink throughout.
Ulcerative lymphangitis (limb form): C. pseudotuberculosis infects lymphatics of the lower limbs, causing hard, painful swellings (cording) of lymph vessels, abscess formation along lymph channels, and painful pitting edema. Affected limbs show painful, ulcerating sores. This form is more painful, takes longer to resolve, and carries a higher recurrence risk than the external abscess form.
Internal abscesses (approximately 8-10% of cases): Abscesses form in the lungs, liver, kidney, or abdominal cavity. Signs are more severe and non-specific: prolonged fever, significant weight loss, reduced performance, occasionally colic. Internal pigeon fever is significantly more serious than external -- prognosis is guarded, treatment is prolonged (months), and some horses do not survive. Internal form often goes undiagnosed until the horse is severely ill; chest radiographs and abdominal ultrasound are necessary when internal involvement is suspected.
Diagnosis
Presumptive diagnosis is clinical in endemic areas based on characteristic abscess location and season. Confirmation: culture of abscess contents (pus submitted to a diagnostic laboratory) grows C. pseudotuberculosis reliably when samples are collected properly (deep material from inside the abscess, not just superficial drainage). PCR from abscess fluid is also available and faster than culture. Synergistic hemolysis inhibition (SHI) titer -- a serology test measuring antibodies to C. pseudotuberculosis -- is positive in affected horses and can detect internal form before abscesses are visible, though titer interpretation requires careful clinical context.
Treatment and Management
External abscesses: The primary treatment is allowing natural abscess maturation and drainage. Hot compresses applied to the swelling 15-20 minutes twice daily accelerate maturation. Surgical lancing is performed once the abscess is fully soft and fluctuant (premature lancing before the abscess is mature increases treatment time and risks spreading the infection). After drainage, lavage the abscess cavity with dilute iodine or chlorhexidine solution twice daily until no further discharge occurs. Healing typically takes 2-4 weeks after drainage.
Antibiotic use: Penicillin is effective against C. pseudotuberculosis but is controversial for external abscesses -- some practitioners believe antibiotics slow abscess maturation by limiting the inflammatory response that drives the abscess to point and drain; others use antibiotics in horses with fever or multiple abscesses. Antibiotics are clearly indicated for internal form (long-term penicillin or trimethoprim-sulfa for months).
Biosecurity: Isolate affected horses to prevent fly transmission to other horses. Dispose of abscess drainage material carefully (bury or bag securely -- flies attracted to the purulent material carry the organism). Fly control is the primary prevention: fly sheets, fly masks, topical fly repellents, and reducing fly breeding habitat near the stable.
Sources: Spier et al. (2004) C. pseudotuberculosis review in horses; Pratt et al. (2005) pigeon fever epidemiology in California; Sellon & Long (2007) Equine Infectious Diseases; Merck Veterinary Manual pigeon fever chapter; AAEP biosecurity guidelines.