Equine Ulcerative Lymphangitis Study Guide

Overview and Clinical Importance

Ulcerative lymphangitis is a chronic, suppurative infection of the cutaneous lymphatic vessels in horses, primarily caused by Corynebacterium pseudotuberculosis (biovar equi). This condition is one of three clinical manifestations of C. pseudotuberculosis infection in horses, alongside external abscesses ("pigeon fever") and internal abscesses. Although ulcerative lymphangitis represents only approximately 1-2% of C. pseudotuberculosis infections, it is clinically significant due to its potential for chronic progression, residual limb damage, and significant treatment challenges.

The disease occurs worldwide but is most prevalent in the western and southwestern United States, where environmental conditions favor bacterial survival. Peak incidence occurs during summer and fall months when fly populations are highest, as insect vectors play a crucial role in disease transmission. Understanding ulcerative lymphangitis is essential for the NAVLE, as questions frequently address differential diagnosis, treatment protocols, and the distinction between sporadic, ulcerative, and epizootic forms of lymphangitis.

Anatomy of the Equine Lymphatic System

The equine lymphatic system is remarkably extensive, containing approximately 8,000 lymph nodes compared to only 600 in humans. This system functions as a secondary circulatory system, running parallel to the cardiovascular system. Unlike the blood circulatory system, the lymphatic system has no central pump and relies on skeletal muscle contraction, breathing movements, and intrinsic vessel contractility to propel lymph fluid.