Rhodococcus equi infection
STEPHANIE SPECK
Bundeswehr Institute of Microbiology, Department of Virology and Rickettsiology, Munich, Germany
Rhodococcus equi (synonym: Corynebacterium equi) in the family Nocardiacea is a Gram- positive pleomorphic coc- cobacillus or rod-shaped bacterium capable of fermenting glucose.
It reduces nitrates, is catalase-positive and produces urease. It usually has a capsule and sometimes is weakly acid-fast. Pathogenicity of R. equi is attributed to the ability to persist and multiply in, and eventually destroy, alveolar macrophages. Virulence can be attributed to certain surface proteins (virulence associated protein (Vap) family) and plasmids. Foal virulent strains revealed VapA protein, whereas pig virulent strains express VapB. Phospholipase C and cholesterol oxidase (‘R. equ³ factors’) are also produced and probably play a role in pathogenesis. Rhodococcus equi resembles a soil organism and may be a commensal in the intestine of horses and other herbivores. It is an important cause of suppurative bronchopneumonia, arthritis and abscesses in foals, but it may also cause tuberculosis-like lesions in the lymph nodes of cattle and pigs, as well as granulomatous lesions in the liver of young goats. Infection in other animals is rare and most likely the result of immunosuppression1-41).Submaxillary lymph nodes of 482 wild boar (Sus scrofa) from Hungary were examined for the presence of R equi by culture. Of these wild boars, 12.4% carried R equi, which was comparable to the carrier rate detected among healthy backyard pigs in Hungary(42). Characterization of 82 R. equi isolates obtained revealed that 21 isolates carried the vapB gene corresponding to intermediate virulence, whereas the remaining 62 strains were avirulent. The latter was not unexpected, as avirulent R. equi are widespread in soil. Lesions in wild boars were not described.