Ehrlichia chaffeensis

Ehrlichia chaffeensis

 

Human ehrlichiosis is an arthropod-transmitted infection.

Epidemiology

  • Incidence – 1.7/1,000,000 in U.S.
  • Age – more common in persons >60 years
  • Sex – male predominance
  • Transmission – Ixodes tick
    • Peak infectious season is April through September
    • Infection rate is highest in Southeastern and mid-Atlantic states

Organism

  • Ehrlichiae are small, obligate intracellular bacteria with gram-negative staining walls
  • Human disease
    • E. chaffeensis (human monocytotropic ehrlichiosis, HME)
      • Transmitted by lone star tick (Amblyomma americanum)
      • Major reservoir is in white-tailed deer
    • E . ewingii (human ewingii ehrlichiosis)
    • A. phagocytophilum – formerly called human granlocytotropic ehrlichiosis (HGE), but now known as human granulocytic anaplasmosis (HGA)

Clinical Presentation

  • HGA and HME infections are clinically indistinguishable
  • Fever, headache and malaise within 1 month after exposure
  • Acute infection – progressive leukopenia (often with a left shift), thrombocytopenia and anemia
  • Elderly and immunocompromised patients more prone to severe infections and death

Diagnosis

  • Laboratory testing
    • E. chaffeensis antibody testing by IFA and/or PCR
    • Other laboratory findings – mild-to-moderate elevations of aspartate and alanine aminotransferases, alkaline phosphatase and lactate dehydrogenase
    • Peripheral blood smears (Wrights stained)
      • Morulae are rarely seen
      • Intracytoplasmic inclusions
        • <10% in HME
        • 25-75% in HGA in 18+ week of infection

Differential Diagnosis

  • Babesia
  • Lyme disease
  • Rickettsial disease
  • Francisella
  • Brucellosis

Treatment

  • Antibiotic therapy should be started as soon as possible after onset of symptoms
  • Nonspecific clinical presentation and high fatality rate if HME untreated
  • Serological diagnosis confirmation may take several weeks as convalescent titers are necessary

Prevention

  • Avoidance of tick bites by wearing clothing leaving only minimal skin exposed
  • Prompt removal of ticks

See Also