Raccoons (Procyon lotor), but not rodents, are natural and experimental hosts for an ehrlichial organism related to “Candidatus Neoehrlichia mikurensis”

“Candidatus Neoehrlichia mikurensis” has been reported from a variety of rodent and Ixodes tick species in Europe and Asia. Recently, an ehrlichial organism closely related to “Candidatus Neoehrlichia mikurensis” was cultured from a raccoon (Procyon lotor) from Georgia, USA. To determine prevalence and distribution, we conducted a molecular survey of free-ranging raccoons (n = 197) from 10 populations in 3 states and found that infections were common in tick-infested populations (50–94%). In an effort to determine the host range of this organism, 10 species of rodents (n = 137) trapped in 3 areas where positive raccoons had been detected were tested; all were negative. In addition, captive bred raccoons and several common laboratory animals (mice, rats, and rabbits) were inoculated with the raccoon ehrlichial isolate (strain RAC413). Raccoons became infected with the culture isolate but all other hosts were refractory to infection. The 16S rRNA gene sequence (1379bp) of the RAC413 isolate was most similar (98.4–98.8%) to members of the “Candidatus Neoehrlichia mikurensis” group and phylogenetic analysis confirmed this organism was related to, but distinct from, “Candidatus Neoehrlichia mikurensis”. Based on the molecular and natural history uniqueness of this organism from raccoons, we propose that this represents a novel species in the “Candidatus Neoehrlichia” group of ehrlichial organisms.