Snapshot A 36-year-old woman presents to her primary care physician after a tick bite. She reports having hiked in Alabama last week and found a tick on her arm after the hike. She denies having any rashes. One day ago, she started having subjective fevers, headache, nausea, and vomiting. Her physical exam is unremarkable and does not have any maculopapular rashes or targetoid lesions. A peripheral blood smear shows monocytes with morulae in the cytoplasm, confirming the diagnosis. (Ehrlichia infection) Introduction Classification Ehrlichia chaffeensis/Anaplasma phagocytophilum (formerly Ehrlichia phagocytophila) obligate intracellular, gram-negative bacteria members of the family Rickettsiae transmission lone star tick (Amblyomma americanum) Ixodes species clinical syndrome ehrlichiosis (can be caused by Ehrlichia or Anaplasma) Epidemiology incidence E. chaffeensis southeast and south-central US A. phagocytophilum midwest, California, and Texas risk factors asplenia immunocompromised status outdoor activities travel or residence in endemic areas Pathogenesis the bacteria infects monocytes (E. chaffeensis) or granulocytes (A. phagocytophilum) Associated conditions often co-infected with Lyme disease Prognosis good prognosis with treatment Presentation Symptoms rash is rare flu-like illness fever headache myalgia fatigue nausea and vomiting Physical exam may have hepatomegaly typically has no physical exam findings Studies Peripheral blood smear with Wright or Giemsa stain E. chaffeensis monocytes with morulae, or inclusions, in the cytoplasm A. phagocytophilum granulocytes with morulae in the cytoplasm Labs may have neutropenia detection of immunoglobulin on enzyme-linked immunosorbent assay Making the diagnosis based on clinical presentation and laboratory studies Differential Rocky Mountain spotted fever distinguishing factor maculopapular rash and physical exam findings such as bilateral periorbital edema Treatment Medical doxycycline indication first-line chloramphenicol indication second-line Complications Renal failure