LAUSR

C. ulcerans represents an emerging zoonotic agent of diphtheria, but little is known about its transmission or maintenance among animal reservoirs. In these studies, we identified diphtheria outbreaks among both outdoor- and indoor-housed rhesus macaques and isolated a toxigenic strain of C. ulcerans from a recently infected animal. ABSTRACT Diphtheria is rare in the United States. and many industrialized nations due to development of an effective vaccine, coupled with high vaccination coverage. Although there is continued risk of importation and transmission of Corynebacterium diphtheriae, C. ulcerans has now become the dominant source of diphtheria cases among several European countries. Bearing this in mind, a better understanding of C. ulcerans biology is clearly needed. Here, we identified active transmission of toxigenic C. ulcerans among indoor- and outdoor-housed rhesus macaques based on diphtheria toxin-specific serology assays as well as direct isolation of C. ulcerans from a recently infected animal. In addition to animal-to-animal transmission, we found serological evidence indicative of potential human transmission. Together, these results provide new details on natural Corynebacterium transmission among nonhuman primates and emphasizes the importance of maintaining high vaccination coverage to reduce the risk of potential zoonotic infection. IMPORTANCE C. ulcerans represents an emerging zoonotic agent of diphtheria, but little is known about its transmission or maintenance among animal reservoirs. In these studies, we identified diphtheria outbreaks among both outdoor- and indoor-housed rhesus macaques and isolated a toxigenic strain of C. ulcerans from a recently infected animal. Retrospective analysis indicated that toxigenic Corynebacteria have been circulating among these primates for decades with the potential for rare zoonotic transmission to humans.