Genetic characterization of a novel Ehrlichia chaffeensisgenotype from an Amblyomma tenellumtick from South Texas, USA

Ehrlichia chaffeensisis the causative agent of human monocytotropic ehrlichiosis (HME), a disease that ranges in severity from mild to fatal infection. Ehrlichia chaffeensisis maintained in a zoonotic cycle involving white-tailed deer (Odocoileus virginianus) as the main vertebrate reservoir and lone star ticks (Amblyomma americanum) as its principal vector. Through complete genomic analysis from human ehrlichial isolates and DNA sequences obtained from deer and tick specimens, nine strains of E. chaffeensishave been characterized. Few studies have examined the genetic diversity of E. chaffeensisin ticks, and some of these investigations have identified that the genetic sequences coincide with the circulating strains reported so far. Here, we report the first evidence of E. chaffeensisDNA from an unfed Amblyomma tenellum(formerly Amblyomma imitator) collected in South Texas. We characterized the genetic variation of this E. chaffeensisgenotype using conserved gene markers such as rRNA, dsb, and groEL. We also used gene targets useful to distinguish genotypes, such as the variable length PCR target gene (VLPT) and 120-kDa gene, encoding the tandem-repeat proteins TRP32 and TRP120, respectively. Our results suggest a novel E. chaffeensisgenotype that exhibited greater variability than other genotypes of E. chaffeensisand highlights the role for A. tenellumas a potential vector of E. chaffeensis.