Equis ISSN 2398-2977


Synonym(s): Angiitis

Contributor(s): Nicola Menzies-Gow, Graham Munroe, Vetstream Ltd, Jamie Prutton


  • Cause: immune-mediated hypersensitivity; infection (EVA, EIA, anaplasma, EHV); toxin (including drug-induced); hepatopathy; photo-activated; neoplasia.
  • Signs: edema, erythema, subcutaneous hemorrhage including mucosal petechiae and ecchymosis, crust, ulcers and serum oozing on distal limbs, face, abdomen and ears. Reluctance to move, pyrexia, inappetence, depression and weight loss. Secondary cellulitis, thrombophlebitis, laminitis and pneumonia have been described.
  • Diagnosis: clinical history, histopathology, response to medication.
  • Treatment: treatment of underlying disease; therapeutic antimicrobial therapy; systemic glucocorticoids in immune-mediated disease; NSAIDs. If edema is severe then intensive care may be required for fluid therapy, hydrotherapy and a tracheostomy if laryngeal obstruction occurs.
  • Prognosis: fair with early and aggressive therapy; depends on underlying cause.



Frequently the etiology is not diagnosed.

Predisposing factors


  • Genetic predisposition to hypersensitivity.
  • Physical factors such as blood flow turbulence, hydrostatic vessel pressure, previous endothelial damage.
  • Altered immunoregulatory mechanisms.


  • Abundant sunlight, large areas of non-pigmented skin (photoactivated disease).
  • Vaccination against Streptococcus equi equi.
  • Exposure to any of the infectious causes listed above.
  • Long-term drug therapy.


  • Vasculitis is a general pathological term for inflammation of blood vessels of any type and location regardless of etiology.
  • Can be a primary process or a component of underlying disease.
  • Direct damage to blood vessel wall or immune-mediated hypersensitivity levels → inflammation of the blood vessels (release of vasoactive amines and β-integrins).
  • The small vessels of the skin (mainly post-capillary venules) are typically involved however the syndrome may affect blood vessels of any organ.
  • Vessel damage → edema, hemorrhage → ischemia of tissues normally supplied by damaged vessels (hence wide variety of possible clinical signs).
  • Immune-mediated disease:
    • Antigenic stimulus hypersensitivity (microbe, drug, toxin, foreign proteins, etc).
    • Type III hypersensitivity → deposition of immune-complexes in vessel walls at endothelial basement membrane → complement is activated and neutrophils migrate to site → release of lysosomal enzymes, oxygen radicals, etc → vessel wall necrosis, leakage and luminal compromise → edema, hemorrhage, thrombosis and ischemic tissue damage.
    • Damage to endothelium via changes in cytokine levels results in vascular dysfunction characterized by an increase in vasoconstriction and platelet aggregation.
  • EVA → direct viral damage to vessel wall.
  • Photoactivated damage: pathophysiology is not known unless ingestion of plants, or drugs, containing photodynamic agents has occurred or liver failure leads to an ability to detoxify phylloerythrin.


  • Depends on underlying disease, eg purpura hemorrhagica typically occurs 1-2 weeks after presumed recovery from a Strangles episode.


  • Depends on underlying cause, eg Strangles infection most commonly occurs in animals 2-5 years of age.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • White S D (2009) Cutaneous vasculitis in equines: a retrospective study of 72 cases. Vet Derm 20 (5-6), 600-606 PubMed.
  • Finley M R et al (1998) Paraneoplastic pruritus and alopecia in a horse with diffuse lymphoma. JAVMA 213 (1), 102-104 PubMed.
  • Woods P R et al (1993) Granulomatous enteritis and cutaneous arteritis in a horse. JAVMA 203 (11), 1573-1575 PubMed.
  • Morris D D (1987) Cutaneous vasculitis in horses - 19 cases (1978-1985). JAVMA 91 (4), 460-464 PubMed.

Other sources of information

  • Felipp M J B (2016) Equine Clinical Immunology. Wiley Blackwell, USA. ISBN: 978-1118558874.
  • Giguere S (1997) Vasculitis. In: Current Therapy in Equine Medicine 4. Ed: Robinson N E. W B Saunders, USA. ISBN: 0-7216-2633-5.
  • Smith B P (1996) Large Animal Internal Medicine: Diseases of Horses, Cattle, Sheep and Goats. 2nd edn. Mosby, USA. ISBN: 978-0815177241.