Ehrlichiosis (Human Monocytic Ehrlichiosis, HME)




  • Ehrlichia Chaffeensis: most common etiology of Ehrlichiosis
  • Ehrlichia Ewingii less common etiology of Ehrlichiosis
    • First Discovered in 1999: several cases occurred in Missouri
    • Ehrlichia Ewingii is the Organism Responsible for Canine Granulocytic Ehrlichosis
    • Most Human Ehrlichia Ewingii Infections Occur in Immunocompromised Hosts
  • Ehrlichia Muris-Like Species (NEJM, 2011) [MEDLINE]
    • Cases Reported in Wisconsin and Minnesota


  • Ehrlichiosis is Endemic in Southeast US, South Central US, and Mid-Atlantic US
    • Few Cases Have Been Reported in New England and Pacific Northwest
    • Isolated Cases Have Been Reported in Europe, Africa, and Mexico


General Comments

  • Tick Exposure is the Primary Mode of Transmission (see Tick-Borne Illnesses, [[Tick-Borne Illnesses]])
    • Percentage of Cases Associated with Tick Exposure: 80-90% of cases
    • Percentage of Cases Associated with Tick Bite: 68% of cases


  • Amblyomma Americanum (Lone Star Tick) (see Amblyomma Americanum, [[Amblyomma Americanum]]): principal vector for Ehrlichia Chaffeensis

Animal Reservoir

  • White Tail Deer
    • Although Ehrlichia Chaffeensis Has Been Identified in Coyotes and Goats, Their Roles in Causing Disease in Humans is Unknown

Incubation Period

  • Incubation Period: 5-14 days

Other Modes of Transmission

  • Maternal-Fetal Transmission
  • Blood Transfusion
  • Direct Contact with Slaughtered Deer
  • Renal Transplant (see Renal Transplant, [[Renal Transplant]]): case report


Complete Blood Count (CBC) (see Complete Blood Count, [[Complete Blood Count]])

Peripheral Blood Smear (see Peripheral Blood Smear, [[Peripheral Blood Smear]])

Bone Marrow Biopsy (see Bone Marrow Biopsy, [[Bone Marrow Biopsy]])

Lumbar Puncture (LP) (see Lumbar Puncture, [[Lumbar Puncture]])

Buffy Coat Examination

Polymerase Chain Reaction (PCR) for Ehrlichia DNA


Clinical Manifestations

General Comments

  • Acute Illness (Usually)
    • However, There is a Wide Spectrum of Disease Presentation, Ranging from Subclinical Illness to Subacute Illness to Chronic Illness: cases with fever lasting as long as 51 days have been reported
    • In Studies of Patients with Transfusion-Related Disease, Donors were Reportedly Asymptomatic (Transfusion, 2013) [MEDLINE]
  • Severity of Illness
    • More Severe Disease Occurs in Patients with Immunocompromised States (HIV, etc) or Other Co-Morbid Disease
  • Differentiation from Diseases with Similar Clinical Presentations
    • Ehrlichiosis Must Be Differentiated from Rocky Mountain Spotted Fever (see Rocky Mountain Spotted Fever, [[Rocky Mountain Spotted Fever]])
      • Note: Rocky Mountain Spotted Fever has a higher incidence of rash (and higher mortality rate)

Ehrlichia Chaffeensis Infection

General Comments

  • Incubation Period: 5-14 days
  • Initial Clinical Features
    • Fever (see Fever, [[Fever]])
    • Headache (see Headache, [[Headache]])
    • Leukopenia (see Leukopenia, [[Leukopenia]])
    • Malaise
    • Myalgias (see Myalgias, [[Myalgias]])
    • Rash: occurs in <30% of adult cases (and 60% of childhood cases)
      • Macular
      • Maculopapular
      • Petechial (see Petechiae, [[Petechiae]])
    • Thrombocytopenia (see Thrombocytopenia, [[Thrombocytopenia]])
    • Transaminitis (see Elevated Liver Function Tests, [[Elevated Liver Function Tests]])

Cardiovascular Manifestations

  • Congestive Heart Failure (CHF) (see Congestive Heart Failure, [[Congestive Heart Failure]])
    • Epidemiology: may occur in previously normal patients (even without signs of myocarditis)
  • Myocarditis (see Myocarditis, [[Myocarditis]])
  • Pericardial Effusion/Tamponade (see Tamponade, [[Tamponade]])
    • Epidemiology: rare (case reports only)

Dermatologic Manifestations

  • Rash: overall, occurs in a minority of all Ehrlichiosis cases
    • Macular
    • Maculopapular
    • Petechial (see Petechiae, [[Petechiae]])

Gastrointestinal/Hepatic Manifestations

Hematologic Manifestations

  • Hemophagocytic Syndrome (Hemophagocytic Lymphohistiocytosis) (see Hemophagocytic Syndrome, [[Hemophagocytic Syndrome]])
    • Epidemiology: case report in a childhood Ehrlichiosis case
    • Prognosis: resolved with treatment
  • Leukopenia (see Leukopenia, [[Leukopenia]])
    • Diagnosis
      • Neutrophil Count: usually inversely related to the duration of the untreated disease
      • Lymphopenia: occurs early
      • Lymphocytosis with Atypical Lymphocytes: occurs later
  • Thrombocytopenia (see Thrombocytopenia, [[Thrombocytopenia]])

Infectious Manifestations

  • Fever (see Fever, [[Fever]]): common
    • Acute Onset
  • Chills
  • Infectious Complications
  • Sepsis-Like or Toxic Shock-Like Illness (see Hypotension, [[Hypotension]])

Neurologic Manifestations

  • Altered Mental Status/Delirium (see Delirium, [[Delirium]])
    • Diagnosis
      • Lumbar Puncture (LP) (see Lumbar Puncture, [[Lumbar Puncture]]): lymphocytic pleocytosis, elevated CSF protein, mononuclear cell inclusions (representing Ehrlichia morulae)
  • Headache (see Headache, [[Headache]])
  • Malaise
  • Seizures (see Seizures, [[Seizures]])

Pulmonary Manifestations

  • Cough (see Cough, [[Cough]])
    • Epidemiology: occurs in 25-50% of cases
  • Respiratory Failure (see Respiratory Failure, [[Respiratory Failure]])

Renal Manifestations

Rheumatologic Manifestations

Ehrlichia Ewingii Infection

General Comments



Chloramphenicol (see Chloramphenicol, [[Chloramphenicol]])

Tetracyclines (see Tetracyclines, [[Tetracyclines]])