NAVLE Hemic and Lymphatic

Equine Purpura Hemorrhagica Study Guide

March 28, 2026 25 min read 16 views
Purpura hemorrhagica (PH) is an acute, non-contagious, immune-mediated aseptic necrotizing vasculitis in horses. It is characterized by widespread edema, petechial and ecchymotic hemorrhages of the mucous membranes, and subcutaneous tissue swelling.

Overview and Clinical Importance

Purpura hemorrhagica (PH) is an acute, non-contagious, immune-mediated aseptic necrotizing vasculitis in horses. It is characterized by widespread edema, petechial and ecchymotic hemorrhages of the mucous membranes, and subcutaneous tissue swelling. PH is most commonly associated with Streptococcus equi subspecies equi (strangles) infection but can occur following other bacterial or viral infections, vaccination, or idiopathically. Understanding this condition is essential for NAVLE success as it represents a classic example of Type III hypersensitivity in veterinary medicine.

High-YieldPH is the most common cause of vasculitis in horses and typically develops 2-4 weeks after strangles infection or vaccination. It is NOT contagious between horses.
Category Associated Causes
Primary (Most Common) Streptococcus equi subsp. equi (strangles) - 32% of cases
Other Bacterial S. equi subsp. zooepidemicus Corynebacterium pseudotuberculosis (pigeon fever) Rhodococcus equi
Viral Equine influenza virus Equine herpesvirus type 1
Vaccination-Related Strangles vaccine (M-protein or intranasal) - especially in horses with high pre-existing SeM titers
Other Chronic suppurating wounds Idiopathic (approximately 28% of cases)

Etiology and Associated Conditions

Purpura hemorrhagica can develop secondary to various infectious agents and antigenic stimuli. The most common associations include:

NAVLE TipIn a retrospective study of 53 horses with PH, 17 had S. equi exposure, 9 had C. pseudotuberculosis infection, 5 were vaccinated with S. equi M protein, and 15 had no identifiable cause. This distribution is high-yield for exam questions asking about etiology.
Clinical Sign Description and Clinical Significance
Subcutaneous Edema Well-demarcated, pitting edema Distribution: All four limbs (most common), ventral abdomen, head, muzzle, trunk Often warm and painful to palpation May be asymmetric initially
Mucosal Hemorrhages Petechiae and ecchymoses on visible mucous membranes Locations: Gingiva, conjunctiva (greater than 80% of cases), nasal mucosa, vulva May have epistaxis
Systemic Signs Depression and lethargy Anorexia Fever (variable) Tachycardia and tachypnea Reluctance to move (stiffness)
Skin Changes Serum exudation from skin surface (in severe cases) Skin sloughing and necrosis (severe/advanced cases) Fissures and ulceration

Pathophysiology

Type III Hypersensitivity Mechanism

Purpura hemorrhagica is a classic example of a Type III hypersensitivity reaction (immune complex-mediated). The pathogenesis involves the following sequence:

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