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Ehrlichiosis is the general name used to describe several bacterial diseases that affect animals and humans. These diseases are caused by the organisms in the genus Ehrlichia. In the United States, there are currently two ehrlichial species that are known to cause disease in humans: Ehrlichia chaffeensis and Ehrlichia ewingii. Ehrlichia chaffeensis causes human ehrlichiosis also described as human monocytic ehrlichiosis (HME). In addition, human infections with Ehrlichia ewingii have also been documented.


In the United States, ehrlichiae are transmitted by the bite of an infected tick. The lone star tick (Amblyomma americanum) is the primary vector of both Ehrlichia chaffeensis and Ehrlichia ewingii in the United States.


The symptoms of ehrlichiosis may resemble symptoms of various other infectious and non-infectious diseases. The initial signs and symptoms generally include:

  • fever
  • headache
  • fatigue
  • muscle aches

Other signs and symptoms may include:

  • nausea
  • vomiting
  • diarrhea
  • cough
  • joint pains
  • confusion
  • occasionally rash

Symptoms typically appear after an incubation period of 5-10 days following the tick bite. It is possible that many individuals who become infected with ehrlichiae do not become ill or they develop only very mild symptoms.


A diagnosis of ehrlichiosis is based on a combination of clinical signs and symptoms and confirmatory laboratory tests. Your doctor can send your blood sample to a reference laboratory for testing. However, the availability of the different types of laboratory tests varies considerably. Other laboratory findings indicative of ehrlichiosis include low white blood cell count, low platelet count, and elevated liver enzymes.


Ehrlichiosis is treated with a tetracycline antibiotic, usually doxycycline.



Centers for Disease Control and Prevention, USA.