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
Your notes
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.