Actinomyces viscosus endocarditis requiring aortic valve replacement

We report a case of primary Actinomyces viscosus endocarditis, an unusual manifestation of actinomycosis, in a 43-year-old farmer with an indolent febrile illness. As has occurred in previous cases, diagnosis was delayed in part because blood isolates were misidentified. Months later when she required aortic valve and root replacement, histologic exam of the diseased valve revealed branching filamentous organisms and the original blood isolates were retrospectively confirmed to be Actinomyces viscosus.