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The Ehrlichioses. William Kwan UNC Medicine-Pediatrics. Objectives. Overview of 3 human Ehrlichioses Microbiology Epidemiology Diagnosis Treatment. Microbiology of Ehrlichiae. Gram-negative obligate intracellular bacteria that grow in vacuoles (morulae)

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The ehrlichioses

The Ehrlichioses

William Kwan

UNC Medicine-Pediatrics


  • Overview of 3 human Ehrlichioses

  • Microbiology

  • Epidemiology

  • Diagnosis

  • Treatment

Microbiology of ehrlichiae
Microbiology of Ehrlichiae

  • Gram-negative obligate intracellular bacteria that grow in vacuoles (morulae)

  • Two Ehrlichiae species and Anaplasma cause three forms of human Ehrlichioses

    • Ehrlichia chaffeensis

    • Ehrlichia ewingii

    • Anaplasma phagocytophila

Human monocytic ehrlichiosis hme
Human Monocytic Ehrlichiosis (HME)

  • Agent: Ehrlichia chaffeensis

  • Vector: Lone Star tick (and sometimes Dog tick)

  • Higher prevalence during late spring and early summer

  • Southeast, south central, and mid-Atlantic

  • Fever (97%), malaise (84%), headache (81%), myalgia (68%)

  • Diarrhea (25-68%), rash (36%, but only 6% at presentation), confusion (20%)

  • Complications: ARDS, meningoencephalitis, fulminant infection, hemorrhage

  • Mortality in 2-5%

  • Leukopenia (60-74%), thrombocytopenia (72%), elevated LFT’s (90%)

Human monocytic ehrlichiosis hme1
Human Monocytic Ehrlichiosis (HME)

  • Diagnosis based on clinical suspicion

  • Most common diagnostic test: Serology using indirect fluorescence antibody to E. chaffeensis

    • Fourfold rise in titers between acute sera (on presentation) and convalescent sera (drawn 2-4 weeks later)

    • Single titer of 1:128 may be diagnostic but no established threshold

Human monocytic ehrlichiosis hme2
Human Monocytic Ehrlichiosis (HME)

  • Peripheral blood smear or examination of buffy coat may show rare morulae (1-20%)

Human monocytic ehrlichiosis hme3
Human Monocytic Ehrlichiosis (HME)

  • Peripheral blood smear or examination of buff coat may show rare morulae (1-20%)

  • PCR techniques being developed

  • Immunochemical staining of tissue (e.g. lymph nodes, liver, spleen, lung)

Human monocytic ehrlichiosis hme4
Human Monocytic Ehrlichiosis (HME)

  • Treatment of choice: Doxycycline 100mg bid x 10 days or up to 3-5 days following defervescence

  • Alternative choice: Rifampin 300mg x 7-10 days

  • Pregnancy:

    • If disease not life-threatening: Rifampin

    • If disease life-threatening: Doxycycline

Human granulocytic anaplasmosis hga
Human Granulocytic Anaplasmosis (HGA)

  • Formerly called Human Granylocytic Ehrlichiosis

  • Agent: Anaplasma phagocytophila

  • Vector: Deer tick

  • Higher prevalence during late spring and early summer

  • Northeast

  • Symptoms are very similar to those in HME

    • Exception: Rash is very rare

  • Leukopenia, thrombocytopenia, elevated LFT’s

  • May have concurrent infection with Lyme Disease and much less commonly Babesiosis

Human granulocytic anaplasmosis hga1
Human Granulocytic Anaplasmosis (HGA)

  • Initial diagnosis based on clinical suspicion

  • Serology using IFA to A. phagocytophila

    • Four-fold rise in titers between acute and convalescent sera

  • Peripheral blood smear or buffy coat examination may show morulae (20-80%, higher than for HME)

  • PCR

  • Immunochemical tissue staining

  • Treatment is same as for HME: Doxycycline (or Rifampin)

Ehrlichiosis ewingii
Ehrlichiosis Ewingii

  • Agent: E. ewingii

  • Vector: Lone Star tick

  • Higher prevalence during summer

  • Symptoms similar to HME but less severe

  • Usually diagnosed in immunocompromised

  • IFA utilizes E. chaffeensis antigen

  • No criteria for diagnostic serologies

  • Treat with Doxycycline

Take home points
Take-Home Points

  • HME and HGA are very similar diseases

  • HME more common in southeast, south central, mid-Atlantic

  • HGA more common in northeast

  • HGA may be accompanied by Lyme Disease

  • Treatment is Doxycycline 100mg bid x 7-10 days or up to 3-5 days after defervescence

  • Rifampin may be used in pregnant patients with non-life threatening disease

  • Bacteria cartoons are corny


  • Dumler et al., “Ehrlichioses in Humans: Epidemiology, Clinical Presentation, Diagnosis, and Treatment.” The Journal of Clinical Infectious Diseases. July 2007; 45: S45-51.

  • Kasper et al., Harrison’s Principles of Internal Medicine. 16th ed. New York: McGraw Hill, 2005.

  • Sexton et al., “The Human Ehrlichioses.” UpToDate Online.

  • Stone et al., “Human Monocytic Ehrlichiosis.” Journal of the American Medical Association. November 10, 2004; 292: 2263 - 227.