Use of Thoracic Ultrasound for the Prevention of Rhodococcus equi Pneumonia on Endemic Farms

1. Introduction
The most common cause of severe pyogranulomatous pneumonia in foals from the age of 4 wk to 3 mo is Rhodococcus equi. ^1–4  R. equi is a facultative intracellular coccobacillus that is found around the world in soil and air samples.^3,5  The virulence mechanisms of R. equi are associated with the virulence plasmid. These 80–90 kb plasmids encoding a family of seven closely related virulence-associated proteins designated VapA and VapC to VapH are responsible for the ability of R. equi to persist in and eventually, destroy alveolar macrophages.⁶  Recent epidemiologic evidence indicates that foals that develop R. equi pneumonia are most commonly infected during the first few days of life. However, clinical signs do not develop until foals are 30–60 days of age or older.⁷  Infection by the organism results in the development of suppurative abscesses that can cause several clinical signs that may include high fevers, cough, elevated respiratory rate and effort, depression, and weight loss.²  The most common location of R. equi disease in foals is the lungs. However, it can also infect various other body systems.⁸  These conditions are classified as extra pulmonary disease (EPD) manifestations of R. equi, and they can include abdominal abscessation, spinal-cord abscessation, enteritis or colitis, hepatitis, septic arthritis, polysynovitis, and uveitis.^1,2,9 [...]