Equine Immune Deficiency Syndromes – NAVLE Study Guide

Overview and Clinical Importance

Immune deficiency syndromes in horses represent a group of disorders characterized by dysfunction or absence of critical components of the immune system. These conditions result in increased susceptibility to infections and are important differentials in foals and young horses presenting with recurrent or persistent infections that fail to respond to conventional therapy. Understanding these syndromes is essential for the NAVLE, as they represent both diagnostic challenges and opportunities for genetic counseling in breeding programs.

Primary immunodeficiencies are congenital disorders where immune system components fail to develop properly, while secondary immunodeficiencies are acquired conditions resulting from external factors such as failure of passive transfer (FPT). This guide focuses on primary immune deficiency syndromes, which often have genetic bases and breed predispositions crucial for NAVLE examination questions.

Classification of Equine Immunodeficiency Disorders

Severe Combined Immunodeficiency (SCID)

Pathophysiology

SCID is an autosomal recessive inherited condition affecting Arabian and part-Arabian horses. The disease results from a 5-base pair deletion in the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) gene. This enzyme is essential for V(D)J recombination, the process required for generating diverse antigen receptors on B and T lymphocytes.