Ehrlichia ewingi - MegaMicro

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Ehrlichia ewingi

Micro > Bacteriology > Intracellular bacteria > Anaplasmataceae
Bacterial structure: obligate intracytoplasmic, aerobic, gram-negative rod

Pathobiology: Parasitize granulocytes, erythrocytes, platelets, and monocytes by remaining in phagocytic vacuoles and disrupting lysosomal fusion. Bacteria cycle between replicating elementary bodies and infectious reticulate bodies that cluster into membrane-encapsulated morulae and are released on cell lysis. Pro-inflammatory cytokine release by unknown mechanism is believed to cause pathology during morulae release.

Clinical presentation, Epidemiology, Reservoir, Vector:
  • Human anaplasmosis due to Erlichia ewingii
    •  
    • Presentation 5-10 days after tick bite. high fever,      headache, malaise, myalgias. Late onset rash in <10% of cases. Leukopenia,      thrombocytopenia, elevated serum transaminases.
    • Infects Neutrophils (similar to A. phagocytophilum)
    •  
    • Epidemiology:
      • mid-April-October
      •   
      • E. ewingii seen in Missouri
      •  
         
    • Reservoir: presumed to be small mammals
    •  
    • Vector: Lone star tick
      •  
Laboratory testing:
  • Poor Gram staining
  • Peripheral Blood Smear: Giemsa-stain: Morulae detected in 10% of monocytic     ehrlichiosis.
  • Nucleic acid amplification (PCR): currently the only test available for E ewingii
  • Serology:     not available
Therapy: Doxycycline upon suspicion of ehrlichiosis. Rifampicin is second line or used for patients who cannot tolerate tetracyclcine class of antibiotics. Other classes of antibiotics are ineffective.
Prevention: avoid tick-infested areas. Prompt removal of embedded ticks. Wearing of PPE. Use of insect repellents. No vaccination available.
DDx:
  • Rocky Mountain Spotted Fever: Rash (macular) present in     90% of patients
  • Meningitis: Need patient history
  • Influenza: Need patient history
  • Infectious mononucleosis: Need patient history
  • Typhus: Need patient history
    •  
    • Brush typhus: travel to Russia, Japan, Middle East and      Orient
    •  
    • Epidemic typhus: exposure to "war-time      environment"
Related concepts

Key Words
canine ehrlichiosis
Tick Borne Disease
Lone star tick
Missouri
Mid-west

 
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