• 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
    • States with the highest incidence:[2]
      • Rhode Island (36.5 cases per million)
      • Minnesota (3.9 to 12.3 cases per million)
      • Connecticut (8.1 to 15.9 cases per million)
    • People often unaware they are bitten with case fatality rate of approximately 1.8%[3]
    • More severe disease in immunocompromised patients (HIV, Elderly, Asplenic)
Lone Star Tick (preserved

Clinical Features

Differential Diagnosis

Tick Borne Illnesses


  • Peripheral blood smear[4]
  • 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


antibiotics should be continued for 5 days after the last recorded fever

  • Adults: Doxycycline 100mg PO/IV BID x 14 days
  • Pediatrics: under 45 kg use Doxycycline 2.2mg/kg PO/IV twice a day
  • Pregnant: Rifampin 300mg PO every 12 hours


  • most cases of Ehrlichiosis are treated as an outpatient

See also


  1. CDC. Ehrlichiosis.
  2. Sexton DJ and McClain MT. Human ehrlichiosis and anaplasmosis. UpToDate.
  3. CDC