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Ehrlichia species

Ehrlichia is a genus of rickettsiales bacteria. They are transmitted by ticks. Several species can cause infection (Ehrlichiosis) in humans.

Background:

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Rickettsia

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>Ehrlichia species, Anaplasma
     1] Anaplasma phagocytophilum (Ehrlichia phagocytophilum)
     2] Ehrlichia chaffeensis
     3] Ehrlichia ewingii
     4] Ehrlichia ewubguum

Anaplasma is a genus of rickettsiales bacteria. May reside in host red blood cells and lead to the disease anaplasmosis (most commonly occurs in tropical areas of the world). Anaplasmas require intermediate tick hosts for maturation.   

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Anaplasma phagocytophilum

  • Formerly Ehrlichia phagocytophilum.
  • Gram-negative, small, obligate, intracellular bacterium of neutrophils.
  • Causes human granulocytic anaplasmosis (tick-borne rickettsial disease).
  • Since 1990, incidence of this disease has increased.  
  • Symptoms include fever, headache, absence of skin rash, leucopenia, thromboctytopenia and mild hepatic injury.

 

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Ehrlichia chaffeensis:  

  • Obligate intracellular gram-negative species of rickettsiales bacteria.
  • Causative agent of human monocytic ehrlichiosis (spread through tick infection; known to infect monocytes. ).

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Therapy:

Important considerations:  The choice of an agent should be based on local antimicrobial sensitivities, site of infection, cost, and comorbid conditions.   Generally, the most common agents/regimens are listed first.   Listed dosages may need to be adjusted for renal dysfunction. 

  1. Doxycycline 100mg orally twice daily [Range: 100-200mg in 1-2 divided doses]
  2. Ciprofloxacin 500-750 mg orally q12h or 200-400mg IV q12h
  3. Levofloxacin 500 – 750 mg IV/PO once daily
  4. Chloramphenicol 50-100 mg/kg/day in divided doses every 6 hours (Maximum daily dose is 4 grams e.g. 1 gram q6h)
  5. Rifampin 300-450 mg  orally/IV q12h

Ehrlichia species