NAVLE Respiratory

Equine Rhodococcus equi Pneumonia in Foals – NAVLE Study Guide

Rhodococcus equi is a gram-positive, facultative intracellular bacterium that causes chronic suppurative bronchopneumonia with abscessation in foals aged 1-5 months.

Overview and Clinical Importance

Rhodococcus equi is a gram-positive, facultative intracellular bacterium that causes chronic suppurative bronchopneumonia with abscessation in foals aged 1-5 months. It is the most common and serious cause of pneumonia in young foals and represents a significant economic burden on endemic breeding farms due to prolonged treatment, surveillance costs, and mortality rates of 20-40%.

The disease is insidious in onset, meaning clinical signs often do not appear until pulmonary infection has reached a critical mass. This characteristic makes early detection challenging but crucial for successful treatment outcomes. R. equi is a soil saprophyte found worldwide, with airborne transmission via dust inhalation being the primary route of infection in foals.

High-YieldOn the NAVLE, R. equi should be at the top of your differential list when presented with a foal aged 1-5 months with chronic progressive pneumonia, pulmonary abscessation, and hyperfibrinogenemia. The combination of macrolide plus rifampin is the gold standard treatment.
Feature Description
Gram Stain Gram-positive, pleomorphic coccobacillus (rod-to-coccoid)
Acid-Fast Staining Partially acid-fast (weakly positive with 1% H2SO4)
Colony Morphology Salmon-pink to yellow, mucoid, non-hemolytic colonies on blood agar after 48-72 hours
Growth Requirements Obligate aerobe; grows on non-enriched media; optimal temperature 30-37°C
Biochemical Tests Catalase-positive, urease-positive, oxidase-negative; non-motile
Environmental Reservoir Soil saprophyte; enriched by herbivore feces; resistant to environmental stresses

Etiology and Epidemiology

Organism Characteristics

Rhodococcus equi (formerly Corynebacterium equi) belongs to the Nocardiaceae family, which also includes Mycobacterium and Nocardia species. Key microbiologic features include:

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