For years foal owners have struggled with controlling the bacterium Rhodococcus equi and the infections it causes—some farms manage cases annually, despite following strict farm management strategies to reduce risk of infection. Resulting pneumonia and diarrhea can be deadly for foals, and treating survivors is costly and labor-intensive.

According to Noah Cohen, VMD, MPH, PhD, Dipl. ACVIM, preventing and controlling R. equi infections might be the ideal way to deal with some farms’ recurrent R. equi problems. However, during a presentation at the 56th Annual Convention of the American Association of Equine Practitioners, held Dec. 5-8 in Baltimore, Md., he said that finding the means to prevent and control R. equi infections is still a challenge that researchers face.

Cohen said that two options for controlling and preventing R. equi infections were recently the subjects of several peer-reviewed studies: chemoprophylaxis and immunoprophylaxis.

Chemoprophylaxis (the use of antimicrobial agents to prevent foal pneumonia), was considered as an option for preventing R. equi infections, Cohen said. Cohen cited two studies in which researchers used azithromycin in an attempt to prevent infections, one of which showed a 76% reduction in the risk of contracting an infection. The other study, however, showed little difference between the infection risk of foals treated with azithromycin and those untreated. Cohen said the reason for the discrepancies in the results is unknown. But the reason for the discrepancy is moot; using azithromycin for preventing R. equi infections should not become common practice because it could create microbial-resistant bacteria in the foal and its environment. If the foal subsequently contracts an R. equi infection, the prognosis would be worse due to the resistant bacteria (which can be shed by carriers and picked up by other foals, resulting in them contracting a resistant form of infection)