Proposal to reclassify Ehrlichia muris as Ehrlichia muris subsp. Muris subsp. nov. and description of Ehrlichia muris subsp. eauclairensis subsp. nov., a newly recognized tick-borne pathogen of humans

We have previously described a novel taxon of the genus Ehrlichia (type strain Wisconsin^T), closely related to Ehrlichia muris, that causes human ehrlichiosis among patients with exposures to ticks in the upper midwestern USA. DNA from this bacterium was also detected in Ixodes scapularis and Peromyscus leucopus collected in Minnesota and Wisconsin. To determine the relationship between the E. muris-like agent (EMLA) and other species of the genus Ehrlichia phenotypic, genotypic and epidemiologic comparisons were undertaken, including sequence analysis of eight gene loci (3906 nucleotides) for 39 EMLA DNA samples and the type strain of E. muris AS145^T. Three loci were also sequenced from DNA of nine strains of E. muris from mouse spleens from Japan. All sequences from E. muris were distinct from homologous EMLA sequences, but differences between them were less than those observed among other species of the genus Ehrlichia. Phenotypic comparison of EMLA and E. muris revealed similar culture and electron microscopic characteristics, but important differences were noted in their geographic distribution, ecological associations and behavior in mouse models of infection. Based on these comparisons, we propose that type strain WisconsinT represents a novel subspecies, Ehrlichia muris subsp. eauclairensis,subsp. nov. This strain is available through the Centers for Disease Control and Prevention Rickettsial Isolate Reference Collection (CRIRC EMU002^T) and through the Collection de Souches de l’Unité des Rickettsies (CSURP2883 ^T). The subspecies Ehrlichia muris subsp. muris subsp. nov. is automatically created and the type strain AS145^T is also available through the same collections (CRIRC EMU001^T, CSUR E2^T). Included is an emended description of E. muris.