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  • Bacterial infection of the family Anaplasmataceae common in mammals such as cattle, dogs, sheep, goats, and horses[1]
  • Spread by the Lonestar tick (Amblyomma americanum)
    • Eastern seaboard from Florida to Maine and as far west as Iowa and Texas
    • People often unaware they are bitten with case fatality rate of approximately 1.8%[2]
    • More severe disease in immunocompromised patients (HIV, Elderly, Asplenic)
Lone Star Tick (preserved

Clinical Features

  • Fever, chills, headache, malaise, myalgias, nausea, vomiting, diarrhea, conjunctival injection
    • Up to 60% of children may have a rash (30% of adults)

Differential Diagnosis

Tick Borne Illnesses


  • Peripheral blood smear[3]
  • Obligate intracellular organism
    • Smear shows intracellular parasites only 20% of time
  • PCR
    • Most sensitive in first week of illness
  • Indirect Immunoflorescence Assay'
    • Gold Standard
    • Negative 85% of time in first 7 days of illness
    • Compare 2 samples drawn at different times
    • 4 fold increase in titers of second draw is positive
  • Enzyme Immunoassay
    • Qualitative tests, not quantitative
  • Leukopenia, elevated transaminases, thrombocytopenia often present



  • Adults: 100mg PO/IV BID x 14 days
  • Children: (under 45 kg): 2.2mg/kg body weight twice a day


  • most cases of Ehrlichiosis are treated as an outpatient

See also


  1. CDC. Ehrlichiosis.
  2. CDC