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Ehrlichiosis is a topic covered in the 5-Minute Emergency Consult.

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  • Tick-borne human infection presenting as a nonspecific febrile illness
  • Several forms of ehrlichiosis exist; 2 predominate in North America
    • Human monocytic ehrlichiosis (HME), 1st described in 1987:
      • Vector tick: Amblyomma americanum (lone star tick)
      • Geographic range: Central, southern, and mid-Atlantic states, with range expanding to parts of New England
    • Human granulocytic ehrlichiosis or human granulocytic anaplasmosis (HGE or HGA), 1st described in 1994:
      • Vector tick: Ixodes scapularis (deer tick)
      • Geographic range: East Coast, mid-Central States, and Pacific Northwest (same areas as Lyme disease which is more common in US than HME)
  • All are tick borne but have different vectors and geographic ranges. Other species have been reported, but at present HME and HGE are the important ehrlichial human pathogens.


  • 2 distinct species of obligate intracellular organisms
  • The taxonomy of these pathogens has changed in recent years as more DNA and ribosomal RNA data become available.
  • HME is caused by the organism Ehrlichia chaffeensis.
  • HGE/HGA is caused by Anaplasma phagocytophila (a new name as of 2002).
  • The vasculitis found in Rocky Mountain spotted fever (RMSF) is usually not present.
  • A 3rd type may also be encountered, caused by Ehrlichia ewingii, which has the tick vector of the lone star tick. Clinically similar to HME.
  • Compared with RMSF, older individuals are usually affected, commonly >40 yr of age.

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Rosen, Peter, et al., editors. "Ehrlichiosis." 5-Minute Emergency Consult, 5th ed., Lippincott Williams & Wilkins, 2016. Emergency Central, emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307397/all/Ehrlichiosis.
Ehrlichiosis. In: Rosen P, Shayne P, Barkin AZ, et al, eds. 5-Minute Emergency Consult. 5th ed. Lippincott Williams & Wilkins; 2016. https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307397/all/Ehrlichiosis. Accessed April 25, 2019.
Ehrlichiosis. (2016). In Rosen, P., Shayne, P., Barkin, A. Z., Wolfe, R. E., Hayden, S. R., Barkin, R. M., & Schaider, J. J. (Eds.), 5-Minute Emergency Consult. Available from https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307397/all/Ehrlichiosis
Ehrlichiosis [Internet]. In: Rosen P, Shayne P, Barkin AZ, Wolfe RE, Hayden SR, Barkin RM, Schaider JJ, editors. 5-Minute Emergency Consult. Lippincott Williams & Wilkins; 2016. [cited 2019 April 25]. Available from: https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307397/all/Ehrlichiosis.
* Article titles in AMA citation format should be in sentence-case
TY - ELEC T1 - Ehrlichiosis ID - 307397 ED - Rosen,Peter, ED - Shayne,Philip, ED - Barkin,Adam Z, ED - Wolfe,Richard E, ED - Hayden,Stephen R, ED - Barkin,Roger M, ED - Schaider,Jeffrey J, BT - 5-Minute Emergency Consult UR - https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307397/all/Ehrlichiosis PB - Lippincott Williams & Wilkins ET - 5 DB - Emergency Central DP - Unbound Medicine ER -