Bovine Paratuberculosis (Johne's Disease) – NAVLE Study Guide

Overview and Clinical Importance

Paratuberculosis (also known as Johne's disease, pronounced "YO-nees") is a chronic, progressive, granulomatous enteritis of ruminants caused by Mycobacterium avium subspecies paratuberculosis (MAP). This disease represents one of the most economically significant infectious diseases affecting the global cattle industry, with annual losses estimated at $198-250 million in the United States alone.

The disease is characterized by a prolonged subclinical phase lasting 2-10 years before clinical signs appear, making early detection extremely challenging. Approximately 68% of U.S. dairy herds have at least one infected animal, with herd prevalence approaching 100% in large dairy operations.

Etiology

Mycobacterium avium subspecies paratuberculosis (MAP) is a small (0.5 x 1.5 micrometers), acid-fast, Gram-positive, obligate intracellular bacterium. MAP is closely related to Mycobacterium avium (99% genetic similarity) but is distinct from Mycobacterium bovis and Mycobacterium tuberculosis.