Geographic distribution and genetic diversity of the Ehrlichia sp. from Panola Mountain in Amblyomma americanum

We developed a sensitive PCR assay based on the conserved gltA (citrate synthase) gene and tested DNA samples extracted from 1964 field-collected and 1835 human-biting Amblyomma americanum from 23 eastern states of the USA.The novel agent was detected in 36 ticks collected from 10 states between 1998 and 2006. Infected ticks were collected both from vegetation (n = 14, 0.7%) and from humans (n = 22, 1.2%). Fragments of the conserved gltA gene and the variable map1 gene were sequenced from positive samples. Two distinct clades, with 10.5% nucleic acid divergence over the 730 bp map1 sequence, were identified.These data suggest that the Panola Mountain Ehrlichia was not recently introduced to the United States; this agent has an extensive distribution throughout the range of its tick vector, has been present in some locations for several years, and displays genetic variability. Furthermore, people in several states were exposed to this agent through the bite of infected ticks, underscoring the potential public health risk of this emerging ehrlichiosis.A novel Ehrlichia transmitted by Amblyomma americanum (lone star ticks) was recently discovered in Panola Mountain State Park, Georgia, USA. The "Panola Mountain Ehrlichia" (PME), which is closely related to E. ruminantium, caused transient febrile illness, followed by chronic latent infection, in a goat [1]. This agent was also associated, using PCR and sequencing, with a case of human illness following a bite from a nymphal Amblyomma acquired at Panola Mountain State Park [2]. White-tailed deer (Odocoileus virginanus) are a probable vertebrate reservoir for PME in the United States; deer are susceptible to infection, are naturally exposed to the agent, and are competent reservoirs for tick transmission of this agent [3].Ehrlichia ruminantium is endemic in southern Africa and the Caribbean, and its pathogenicity in cattle, sheep, and goats varies from mild febrile illness to fatal heartwater [4-7]. Several species of Am