Emerging Tick-Borne Illnesses: Not Just Lyme Disease Part 3 Ehrlichiosis




  • Overall annual incidence noted to be 3.2 cases per million in the United States between 2008 and 2012 (Biggs 2016)
  • Highest incidence occurs in those 60-69 years of age (Biggs 2016)


  • Median age is 55 years of age with 64% of cases reported in Caucasian patients (Heitman 2016)


  • Slight male to female predominance (Heitman 2016)


  • Case fatality rate is estimated to be 0.7-1% overall (Heitman 2016).
    • Case fatality rate is highest in those over under 5 years of age and over 70 years of age

Geography and Seasonality (Heitman 2016): Cases most frequently reported in the Southeastern and Southcentral United States

  • Six States account for over 54% of all reported cases
    • Oklahoma
    • Missouri
    • Delaware
    • Arkansas
    • Missouri
    • Tennessee
  • Seasonal distribution is concentrated from May through July

Poor Prognostic Factors (Biggs 2016):

  • Increased Age
  • Immunocompromised States
  • Delays in diagnosis and treatment
  • Use of sulfonamide antimicrobial

Pathogenesis (Biggs 2016):

  • After tick transmissibility, chaffennis, an obligate intracellular bacterial, has a predilection for monocytes and tissue macrophages, specifically neutrophils
  • Once infected, the organism multiplies within cytoplasmic membrane-bound vacuoles forming clusters of bacterial called morulae
  • Infection elicits a systemic inflammatory response with multiorgan involvement, particularly the spleen, lymphatic system, and bone marrow

History and Physical:

Symptoms (Biggs 2016):

  • Symptoms typically appear 5-14 days after bite of an infected tick
  • Rash is present more often than Anaplasmosis
    • Present in up to 1/3rd of patients
    • Typically occurs 5 days after illness onset
  • Fever occurs in 96% of recognized cases of ehrlichiosis along with other non-specific flu-like symptoms:
    • Headache
    • Malaise
    • Myalgias
  • Gastrointestinal symptoms are often seen unlike Anaplasmosis
    • Very commonly seen in children
  • Respiratory symptoms or Cough is present in approximately 28% of patients
  • Central Nervous System involvement is present in approximately 20% of patients
    • Meningitis and Meningoencephalitis
  • Severe Manifestations: Most cases are self-limiting, but Ehrlichiosis has been associated with the following severe disease manifestations:
    • Shock
    • Renal Failure
    • Hepatic Failure
    • Coagulopathy
    • Hemorrhagic Manifestations
    • Hemophagocytic Syndromes
    • ARDS


Labs: Characteristic laboratory findings are seen in Ehrlichiosis along fever and non-specific flu-like illness:

  • Leukopenia
  • Thrombocytopenia
  • Mild Anemia: Occurs later in illness than thrombocytopenia or leukopenia
  • Mild to Moderate Elevated Hepatic Transaminase
  • Mild to Moderate Hyponatremia

Blood Smear:

  • May see morulae with microscopic examination of blood smears but blood smear may be relatively insensitive and inconsistent and is dependent on operator experience (Biggs 2016)
  • Observation of morulae is seen much less commonly than in Anaplasmosis

Confirmatory Testing:

  • Serological testing of IgM and IgG antibodies using indirect immunofluorescence assay (IFA) is available for diagnosis
  • RT-PCR assays is available for diagnosis and is most sensitive during the first week of illness and is the test of choice
  • Immunohistochemical staining of skin, tissue, or bone marrow biopsies has also been used for diagnosis

Guest Post By:

Akash Ray, DO
PGY-2 Emergency Medicine Resident Inspira Medical Center
Vineland, NJ
Twitter: @_kashray


  1. Biggs H et al. Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever and Other Spotted Fever Group Rickettsioses, Ehrlichioses, and Anaplasmosis – United States. MMWR Recomm Rep. 2016. PMID: 27172113
  2. Heitman N at al. Increasing Incidence of Ehrlichiosis in the United States: A Summary of National Surveillance of Ehrlichia chaffeensis and Ehrlichia ewingii Infections in the United States, 2008-2012. Am J Trop Med Hyg. 2016. PMID: 26621561

Post Peer Reviewed By: Salim R. Rezaie, MD (Twitter: @srrezaie)

Cite this article as: Muhammad Durrani, "Emerging Tick-Borne Illnesses: Not Just Lyme Disease Part 3 Ehrlichiosis", REBEL EM blog, November 4, 2020. Available at: https://rebelem.com/emerging-tick-borne-illnesses-not-just-lyme-disease-part-3-ehrlichiosis/.

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