Controversies in therapy of infections caused by Rhodococcus equi in foals
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2017 EVJ Ltd Pneumonia caused by Rhodococcus equi is one of the most important causes of disease and death in foals. R.equi can also be cultured from a large variety of extrapulmonary sites of infection. In the absence of an effective vaccine, ultrasonographic screening for early detection of pulmonary lesions has become routine practice at many farms endemic for pneumonia caused by R.equi. Consequently, the most frequently recognised form of R.equi infection at such farms is a subclinical form in which foals develop sonographic evidence of peripheral pulmonary consolidation or abscessation without necessarily manifesting clinical signs. Evidence exists that not all foals with ultrasonographic lesions will progress to develop clinical signs, and treating a large proportion of foals based on subclinical ultrasonographic findings has been linked to emergence of macrolide- and rifampin-resistant R.equi at a horse farm. Selectively treating only those foals with larger lesion scores and monitoring foals with daily physical inspections and weekly thoracic ultrasonography offers an approach that could decrease antimicrobial drug use without significantly increasing mortality. Current evidence continues to support the combination of rifampin with a macrolide (azithromycin, clarithromycin or erythromycin) for treating clinical infections caused by R.equi despite recently described pharmacological interactions between these drugs. When infection with a macrolide-resistant isolate is confirmed, limited effective alternatives exist.
