Ehrlichia species

Ehrlichia species is a topic covered in the Johns Hopkins ABX Guide.

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  • Cause of tick-borne infection in humans; obligate intracellular pathogens that infect human macrophages and monocytes.
  • Species described as causing human infection:
    • Human monocytic ehrlichiosis (HME): due to Ehrlichia chaffeensis, transmitted by Amblyomma americanum (Lone Star tick, Fig 1) and possibly other tick vectors such as Dermacentor variabilis (American dog tick).
      • Lone star is the most common cause of tick bite in southern U.S. Tick generally in woodland habitats with white-tail deer (thought to be main reservoir).
    • E. ewingii (Ee): canine pathogen that rarely infects humans, infection now termed "human ewingii ehrlichiosis [HEE]."
      • Human cases increasingly described over wider range (10 states), though most to date in Missouri.
    • E. muris: human infection noted in Europe, Russia, Japan/Asia and described in Western U.S. Occurs via tick vector Ixodes persulcatus complex.
    • Ehrlichia species Wisconsin: recently identified[9], close relative of E. muris; likely vector is the Ixodes scapularis tick (same as HGA and B. burgdorferi).
      • Sero-crossreactivity seen with antibodies to E. chaffeensis which may confuse accurate diagnosis.
      • Existing PCR primers for E. chaffeensis and E. ewingii may fail to detect.
      • Usually described as E. muris-like (EML) agent in the literature.
      • Cases to date described in Minnesota and Wisconsin.

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Last updated: July 31, 2016