Microbiology

• 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

Geography

• 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

Transmission

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

Ticks

• 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
  • Packed Red Blood Cells (see Packed Red Blood Cells, [[Packed Red Blood Cells]])
  • Leukoreduced Red Blood Cells
  • Platelets (see Platelet Transfusion, [[Platelet Transfusion]])
• Direct Contact with Slaughtered Deer
• Renal Transplant (see Renal Transplant, [[Renal Transplant]]): case report

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

• Elevated Liver Function Tests (LFT’s) (see Elevated Liver Function Tests, [[Elevated Liver Function Tests]])
• Nausea/Vomiting (see Nausea and Vomiting, [[Nausea and Vomiting]])

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
  • Candidiasis (see Candida, [[Candida]])
  • Herpes Simplex Esophagitis (see Herpes Simplex Virus, [[Herpes Simplex Virus]])
  • Invasive Aspergillosis (see Aspergillus, [[Aspergillus]])
• 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

• Acute Kidney Injury (AKI) (see Acute Kidney Injury, [[Acute Kidney Injury]])

Rheumatologic Manifestations

• Arthralgias (see Arthralgias, [[Arthralgias]])
• Myalgias (see Myalgias, [[Myalgias]])

Ehrlichia Ewingii 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: rarely occurs
  • Thrombocytopenia (see Thrombocytopenia, [[Thrombocytopenia]])
  • Transaminitis (see Elevated Liver Function Tests, [[Elevated Liver Function Tests]])
  • Vomiting (see Nausea and Vomiting, [[Nausea and Vomiting]])