Description of Candidatus Anaplasma nietoi, a tick-borne intracellular bacterium of rodents

Anaplasma phagocytophilum is a gram-negative bacterial pathogen that is occasionally fatal to humans and domestic animals. This zoonotic bacterium is transmitted via the bite of a tick, which usually acquires the pathogen during a blood-meal on an infected wild rodent reservoir host. The taxonomic classification of Anaplasma phagocytophilum has been revised multiple times since its discovery; although currently classified as a single species, it appears to comprise a complex of multiple formally described and provisionally named genospecies. Each A. phagocytophilum genospecies occupies a unique ecological niche, exhibiting specific host tropisms and differing in pathogenicity. Differentiating among genospecies and documenting ecologies could inform targeted and efficient diagnosis, risk assessment, and control measures. The DU1 strain of A. phagocytophilum was detected in seven mammalian species, including six rodent species and five Ixodes tick species, at six geographically distinct locations in northern California. Each location was dominated by coniferous forest subjected to various levels of disturbance. Phylogenetic analyses was performed using groEL, ank and 16S rRNA genes, as well as the 23S-5S intergenic spacer: groEL and ank sequences revealed that DU1 samples form a clade distinct from other A. phagocytophilum genospecies. This strain has not exhibited pathogenicity in rodent hosts or in horses used as an experimental model system for human infection. We propose to name this strain Candidatus Anaplasma nietoi.