Bacterial structure: obligate intracytoplasmic, aerobic, gram-negative
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)
- E. ewingii seen in Missouri
- Reservoir: presumed to be small mammals
- Vector: Lone star tick
- Poor Gram staining
- Peripheral Blood Smear: Giemsa-stain: Morulae detected in 10% of monocytic
- Nucleic acid amplification (PCR): currently the only test available for E ewingii
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.
- 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
- Epidemic typhus: exposure to "war-time