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
  • States with the highest incidence:
    • 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%
  • More severe disease in immunocompromised patients (HIV, Elderly, Asplenic)

Lone Star Tick (preserved

Clinical Features

• Variable spectrum of severity of disease
• Fever/chills (abrupt onset), malaise, myalgias
• Headache
• Nausea/vomiting, diarrhea
• Conjunctival injection
• Rash
  • Up to 60% in children, 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

Evaluation

• 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

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

Disposition

• most cases of Ehrlichiosis are treated as an outpatient

See also

• Tick Borne Illnesses