Rhodococcus equi Pneumonia: Clinical Findings, Diagnosis, Treatment and Prevention

Rhodococcus equi is a Gram-positive facultative intracellular bacterial pathogen and the most common cause of severe infectious pneumonia in foals. The pathogen is ubiquitous in the environment, but becomes concentrated in breeding farm situations due to its ability to reproduce in the gastrointestinal tract of herbivores. Foals may be exposed to the organism soon after birth; overt infection results in variable number of foals due to a combination of pathogen virulence, host susceptibility, and infective dose of the organism. Herd health programs using passive transfer of antibodies, especially with transfusions of equine hyperimmune plasma, can decrease incidence rates on affected premises, but rarely prevent infection in all susceptible individuals. An effective vaccine is not currently available. Combined therapy of clinically affected individuals using macrolide antibiotics combined with rifampin has improved outcome, including both morbidity and mortality.