Bit & Bridle

Equine Ulcerative Lymphangitis

Other Names

  • Equine Ulcerative Lymphangitis
  • Pigeon Fever Lymphangitis (when caused by Corynebacterium pseudotuberculosis)
  • Chronic Ulcerative Lymphangitis
  • Corynebacterial Lymphangitis

What is Equine Ulcerative Lymphangitis?

Equine ulcerative lymphangitis is a specific, chronic form of bacterial lymphangitis characterised by the development of nodular lesions along the lymphatic vessels of the lower limb, which ulcerate and discharge pus. It is distinct from the more acute form of equine lymphangitis (generalised “big leg disease”) — see the equine lymphangitis entry for the broader condition.

Ulcerative lymphangitis most commonly affects the hindlimbs, particularly along the medial (inner) aspect of the lower leg. The disease tends to follow a chronic, relapsing course, with nodules developing, softening, bursting, and temporarily resolving, only to recur nearby. Over time, the repeated cycles of inflammation and scarring lead to permanent thickening and fibrosis of the lymphatic vessels and surrounding tissue — the characteristic “corded” appearance — and can result in persistent limb swelling.

The condition is seen worldwide and can cause significant welfare concerns and persistent lameness in chronically affected horses. Understanding the bacterial cause, transmission, and treatment options is essential for effective management.

Causes

Equine ulcerative lymphangitis is most commonly caused by:

  • Corynebacterium pseudotuberculosis: The primary causative organism. This bacterium is the same one responsible for “Pigeon Fever” (internal and external abscessation) in horses, which is well known in western parts of the USA. It also causes caseous lymphadenitis in sheep and goats. The bacterium is hardy and survives in soil and manure for extended periods. Infection typically occurs through small wounds or abrasions in the skin of the lower limb, or via insect vectors (particularly flies).
  • Other bacteria: Staphylococcus spp., Streptococcus spp., and other opportunistic organisms can occasionally cause a similar clinical picture — culture of discharge is important to identify the specific pathogen.

Risk factors include:

  • Minor skin wounds, abrasions, or insect bites on the lower limbs
  • Muddy or contaminated pastures and paddocks
  • Poor fly control
  • Horses with impaired lymphatic drainage (e.g., those with pre-existing lymphatic damage)
  • Contact with infected horses or contaminated soil

Symptoms and Signs

  • Nodular skin lesions: Hard, pea-to-walnut-sized nodules develop under the skin along the course of lymphatic vessels in the lower limb — most often the medial hindlimb from the fetlock to the stifle region.
  • Ulceration and discharge: The nodules soften, rupture through the skin, and discharge a thick, creamy, sometimes caseous (cheese-like) pus. The discharge may have a characteristic pungent odour.
  • Lymph vessel thickening (“cording”): As the condition becomes chronic, the lymphatic vessels become permanently thickened and palpable as firm “cords” running beneath the skin.
  • Limb swelling: Chronic inflammation and lymphatic obstruction lead to persistent oedema of the affected leg, ranging from mild to pronounced.
  • Lameness: Variable — ranges from absent to moderate lameness, particularly in acute phases when swelling and pain are more marked.
  • Skin thickening and scarring: Longstanding cases develop significant dermal fibrosis around the discharge sites.
  • Recurrence: The disease characteristically recurs, with new nodules forming in the same or adjacent lymphatic channels.

Diagnosis

  • Clinical examination: The pattern of nodular lesions along the medial aspect of the hindlimb, combined with ulceration and discharge, is highly characteristic.
  • Bacterial culture: Discharge or material from an intact nodule should be submitted for aerobic and anaerobic culture. Identifying C. pseudotuberculosis is important because it guides antibiotic selection and confirms the diagnosis. The organism may require specific culture media and anaerobic conditions — inform the laboratory of suspicion when submitting samples.
  • Sensitivity testing: Antibiotic sensitivity should be requested alongside culture, particularly for Corynebacterium.
  • Serology: A blood test (synergistic haemolysin inhibition — SHI test) can detect antibodies to C. pseudotuberculosis, supporting the diagnosis.
  • Differentiation from acute lymphangitis: Acute lymphangitis typically causes dramatic, rapid-onset swelling of the whole limb, with severe pain and systemic illness. Ulcerative lymphangitis is more insidious, chronic, and localised.

Treatment

Equine ulcerative lymphangitis is challenging to treat and often requires prolonged management:

  • Systemic antibiotics: Based on culture and sensitivity results. C. pseudotuberculosis is typically sensitive to penicillin, rifampicin, or combinations thereof. Prolonged courses are usually required — weeks to months — due to the chronic nature of the disease and the intracellular survival of the organism within abscess walls.
  • Surgical drainage: Opening and thorough flushing of intact nodules with antiseptic solutions accelerates drainage and reduces pus accumulation. This is often performed under standing sedation.
  • Wound management: Open ulcerated wounds should be kept clean — daily gentle cleaning with an antiseptic wash and topical application of appropriate wound preparations.
  • NSAIDs: To manage pain, swelling, and inflammation during active phases.
  • Controlled exercise: Gentle, regular movement helps promote lymphatic drainage from the affected limb and reduces oedema. Complete box rest is not ideal.
  • Compression bandaging: Supportive bandaging or stable wraps can help manage persistent limb swelling.
  • Address predisposing factors: Fly control (fly rugs, repellents, stable management), wound management, and clean, dry, well-managed pastures reduce reinfection risk.

Prevention

  • Fly control: Comprehensive fly control measures — fly rugs, repellents, insecticide-treated leg wraps, manure management — are particularly important in regions or seasons where flies are active, as they act as vectors for C. pseudotuberculosis.
  • Wound care: Promptly treat all wounds on the lower limbs, even minor abrasions. Bacteria enter through skin breaks, so keeping wounds clean reduces infection risk.
  • Isolation: Infected horses should ideally be isolated or kept away from clean horses, as the discharge contains high concentrations of the causative bacteria. Clean up and disinfect contaminated areas.
  • Pasture hygiene: Avoid grazing horses on land heavily contaminated with sheep or goat manure (which may carry C. pseudotuberculosis), and maintain good overall pasture hygiene.
  • Protective leg wraps: During fly season or in contaminated environments, protective lower limb wraps may reduce insect biting and wound contamination.

Prognosis

The prognosis for equine ulcerative lymphangitis is guarded. Many cases can be managed effectively with long-term treatment, but complete resolution is not always achievable. Horses that respond well to early, aggressive antibiotic treatment and wound management may recover with minimal permanent changes. However, horses with chronic disease and significant lymphatic fibrosis often retain some degree of permanent limb swelling and vessel “cording,” and are at risk of repeated flare-ups — particularly in warm, wet, or fly-heavy seasons. The disease is rarely fatal but can significantly impair the horse’s quality of life and athletic usefulness if not well controlled.

When to Call the Vet

Contact your vet if you notice:

  • Nodular or ulcerated lesions along the inner aspect of the hind leg
  • Discharging wounds on the lower limb that do not heal or keep recurring nearby
  • Persistent or recurring limb swelling with or without discharge
  • Any horse that has had a previous episode of ulcerative lymphangitis and shows new nodule development

Frequently Asked Questions

Is equine ulcerative lymphangitis the same as Pigeon Fever?

They share the same causative organism — Corynebacterium pseudotuberculosis — but are different clinical presentations. Pigeon Fever (so called because of the swelling of the pectoral muscles that resembles a pigeon’s chest) typically involves external chest and ventral abdominal abscesses, or internal abscesses in the chest or abdomen. Ulcerative lymphangitis involves the lymphatic vessels of the limbs. Both can occur in the same horse, and the same organism can be responsible for either condition. Pigeon Fever is more common in parts of the USA; ulcerative lymphangitis occurs worldwide.

Can I catch ulcerative lymphangitis from my horse?

Corynebacterium pseudotuberculosis can rarely cause disease in humans — reports of human cases exist, typically causing lymphadenitis, and usually in people with close contact with infected animal discharge. The risk is considered low but non-negligible. Wear gloves when handling discharge from affected wounds, wash hands thoroughly after contact, and inform your vet if you develop any skin lesions or swollen lymph nodes after working with an affected horse.

How long will my horse need antibiotics?

Treatment with antibiotics is typically prolonged — many cases require 4–8 weeks or longer of systemic antibiotic therapy, combined with ongoing local wound management. Premature discontinuation of antibiotics often results in relapse. Your vet will guide the duration based on clinical response, culture results, and monitoring. Patience and consistency are key — this is not a condition that resolves in a matter of days.

Why does the infection keep coming back?

Recurrence is common in equine ulcerative lymphangitis for several reasons: the causative bacteria can survive in the environment (soil, manure) for prolonged periods; once established, C. pseudotuberculosis forms walled abscesses that are difficult for antibiotics to penetrate fully; and horses with pre-existing lymphatic damage are more vulnerable to reinfection. Thorough drainage, prolonged antibiotic treatment, fly control, and addressing wound management in the environment are all necessary to minimise recurrence.