Bacterium
Ehrlichia chaffeensis
Obligate intracellular tick-borne bacterium of monocytes
err-LIK-ee-uh chuh-FEEN-sis
High-yield clue
Mulberry-shaped clusters (morulae) inside monocytes on a blood smear are the classic study clue.
Overview
An obligate intracellular Gram-negative bacterium in the order Rickettsiales that replicates inside monocytes and is the agent of human monocytic ehrlichiosis (HME). It is a high-yield example of a tick-borne intracellular pathogen studied alongside Anaplasma and Rickettsia.
Classification
- Gram-negative
- Obligate intracellular
- Order Rickettsiales
- Family Anaplasmataceae
Lab & identification clues
- Morulae in monocyte cytoplasm vocabulary
- PCR/NAAT detection concept
- Serology (IFA) concept
- Poorly seen on routine Gram stain
Associations
- Lone star tick (Amblyomma americanum) transmission
- White-tailed deer reservoir vocabulary
- Southeastern/south-central US epidemiology
- Fever-headache-myalgia study presentation
Commonly confused with
- Anaplasma phagocytophilum
- Rickettsia rickettsii
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.