Microbiology · Intracellular and atypical bacteria
Ehrlichia / Anaplasma !
- Bacterium
- Gram-negative
- For completeness
Tick-borne bacteria that live inside white blood cells; they cause fever with low white cells and platelets.
Updated 2026-11-01
Also called: ehrlichiosis, anaplasmosis
At a glance
- Gram
- Gram-negative
- Shape
- Small cocci clustered in morulae
- Oxygen
- Obligate intracellular (white blood cells)
- Family
- Anaplasmataceae
- Stain
- Giemsa or Wright on smear: morulae in the cytoplasm
Morphology
- Morulae: mulberry-like bacterial clusters inside vacuoles
- Ehrlichia chaffeensis in monocytes; Anaplasma phagocytophilum in neutrophils
Transmission
- Tick bites: Amblyomma americanum (Ehrlichia) and Ixodes (Anaplasma)
- Rarely by transfusion
Reservoir: Deer, rodents and other mammals; dogs for some Ehrlichia species
Vector: Lone star tick (Amblyomma americanum) and Ixodes
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- Live in white-cell vacuoles and avoid being killed
- Impair white-cell function and drive systemic inflammation
Diseases it causes
- Human monocytic ehrlichiosis and human granulocytic anaplasmosis
Clinical picture
- Fever, chills, severe headache and myalgia one to two weeks after the bite
- Rash is uncommon (more frequent in children with ehrlichiosis)
- Severe forms: respiratory failure, bleeding, multi-organ failure in older or immunosuppressed people
Diagnosis
- Leukopenia, thrombocytopenia and raised transaminases
- Blood PCR: most useful test in the acute phase
- Morulae on smear (more frequent in anaplasmosis)
- Serology with paired samples
Treatment
Doxycycline at any age, started on suspicion without waiting for results.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Avoid tick bites: repellents, long clothing, body checks
- Tick control on pets
Test yourself
Think of the answer, then tap the question to see it.
In which cell are Anaplasma phagocytophilum morulae seen?
In neutrophils (granulocytes).
Which lab findings are typical of ehrlichiosis?
Leukopenia, thrombocytopenia and raised transaminases.
What is the treatment of choice for ehrlichiosis?
Doxycycline, in adults and children of any age.
Related
← Back to the group: Intracellular and atypical bacteria
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: About Ehrlichiosis | Ehrlichiosis | CDC (Centers for Disease Control and Prevention (CDC), 2024); About Anaplasmosis | Anaplasmosis | CDC (Centers for Disease Control and Prevention (CDC), 2024).
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Representative model, for educational purposes only.