Bacterium
Anaplasma phagocytophilum
Intracellular tick-borne bacterium of granulocytes
an-uh-PLAZ-muh fag-oh-sy-TOF-ill-um
High-yield clue
Morulae inside neutrophils (granulocytes) distinguish it from Ehrlichia, which parasitizes monocytes.
Overview
An obligate intracellular Gram-negative bacterium in the order Rickettsiales that infects neutrophils (granulocytes) and causes human granulocytic anaplasmosis (HGA). It is the counterpart to Ehrlichia used to teach the monocyte-versus-granulocyte morulae distinction.
Classification
- Gram-negative
- Obligate intracellular
- Order Rickettsiales
- Family Anaplasmataceae
Lab & identification clues
- Morulae in granulocyte cytoplasm vocabulary
- PCR/NAAT detection concept
- Peripheral smear inclusion concept
- Serology (IFA) concept
Associations
- Ixodes scapularis (black-legged tick) transmission
- Same tick vector as Lyme and Babesia (co-infection vocabulary)
- Summer peak epidemiology
- Northeast/upper-midwest US framing
Commonly confused with
- Ehrlichia chaffeensis
- Borrelia burgdorferi
Frequently asked questions
What is Anaplasma phagocytophilum?
An obligate intracellular Gram-negative bacterium in the order Rickettsiales that infects neutrophils (granulocytes) and causes human granulocytic anaplasmosis (HGA). It is the counterpart to Ehrlichia used to teach the monocyte-versus-granulocyte morulae distinction.
What is the Gram stain of Anaplasma phagocytophilum?
Anaplasma phagocytophilum is Gram negative.
What are the lab clues for Anaplasma phagocytophilum?
Lab clues for Anaplasma phagocytophilum include Morulae in granulocyte cytoplasm vocabulary, PCR/NAAT detection concept, Peripheral smear inclusion concept, and Serology (IFA) concept.
What is Anaplasma phagocytophilum commonly confused with?
Anaplasma phagocytophilum is commonly confused with Ehrlichia chaffeensis and Borrelia burgdorferi.
Original student-study summary. Sources checked: OpenStax Microbiology 2e, NCBI Bookshelf Medical Microbiology, and CDC topic pages where applicable; reviewed 2026-06. Educational only; no diagnosis, treatment, dosing, or specimen-handling guidance.