Ehrlichiosis

Background

• Bacterial infection of the family Anaplasmataceae common in mammals such as cattle, dogs, sheep, goats, and horses
• 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%
  • 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

• Babesiosis
• Colorado tick fever
• Ehrlichiosis
• Heartland virus
• Lyme
• Murine typhus
• Rocky mountain spotted fever
• Southern tick-associated rash illness (STARI)
• Tick paralysis
• Tularemia

Diagnosis

• Peripheral blood smear
• 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

Management

Doxycycline

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

Disposition

• most cases of Ehrlichiosis are treated as an outpatient

See also

• Tick Borne Illnesses