II. Epidemiology

  1. Incidence: 906 reported cases in U.S. in 2014
  2. Outdoor or woods exposure
  3. Majority of cases occur April to September
    1. Highest Incidence in June and July
  4. U.S. regions affected
    1. South central and Southeast (New Jersey and south)
    2. Southern midwest (from Illinois to Texas)
    3. One third of cases are found in Oklahoma, Missouri and Arkansas

III. Pathophysiology

  1. Carried by Lone star tick (Amblyomma americanum)
    1. The less common E. muris eauclairensis is carried by the Deer Tick (Ixodes Scapularis)
  2. Small gram-negative organisms (Neorickettsia)
    1. Pleomorphic
    2. Obligate intracellular organisms
    3. Infect Monocytes
  3. Organisms causing Human Monocytic Ehrlichiosis
    1. Ehrlichia chaffeensis (primary cause)
    2. Ehrlichia ewingii (similar disease in Immunocompromised patients and dogs)

IV. Symptoms (Occur 7-10 days after Tick Bite)

  1. Common Initial Symptoms
    1. Fever
    2. Shaking chills to rigors
    3. Sweats
    4. Myalgia
    5. Headache
  2. Other symptoms
    1. Malaise
    2. Nausea and Vomiting, Anorexia
    3. Abdominal Pain
    4. Diarrhea
    5. Cough
    6. Conjunctival Injection
    7. Confusion

V. Signs: Rash

  1. Present in 30% of patients
  2. Characteristics vary
    1. May be maculopapular or petechial or appear with diffuse erythema
  3. Involves trunk, and spares hands and feet
  4. Not associated with Tick Bite site
    1. Contrast with Erythema Migrans in Lyme Disease

VI. Differential Diagnosis

  1. See Tick Borne Illness
  2. Similar to Anaplasmosis presentation, and Rocky Mountain Spotted Fever Presentation (with different rash)

VII. Labs

  1. Complete Blood Count
    1. Leukopenia
    2. Thrombocytopenia
    3. Mild Anemia (later stages)
  2. Liver transaminases increased
    1. Aspartate Aminotransferase (AST) increased
    2. Alanine Aminotransferase (ALT) increased
  3. Cerebrospinal Fluid
    1. Lymphocytic Pleocytosis
    2. Increased CSF Protein
    3. Ehrlichia PCR
  4. Peripheral Smear
    1. Morulae inclusion bodies
      1. Intracellular mulberry-like clusters of organisms in Monocyte vacuoles
      2. Contrast with the erythrocyte inclusion body of Babesiosis (tetrad or maltese)
  5. Specific testing
    1. Whole Blood Ehrlichia PCR
      1. Most sensitive in first 2 weeks of infection
    2. Ehrlichiosis Serology
      1. Positive two weeks after onset
      2. Used for confirmation, not for diagnosis
      3. Anticipate a fourfold rise in Antibody titers
        1. Minimum peak 1:64
        2. Maximum peak 1:128 or higher dilution
  6. Other variably present laboratory findings
    1. Increased Erythrocyte Sedimentation Rate (ESR)
    2. Increased Blood Urea Nitrogen (BUN)
    3. Increased Serum Creatinine

VIII. Management

  1. General
    1. Coinfection
      1. Concurrent transmission of Lyme Disease and Ehrlichiosis is common
      2. Coninfection with Babesiosis may also occur
    2. Antibiotics for two weeks (minimum of 10 days)
    3. Continue for at least 3 days after fever subsides
  2. Agents
    1. Preferred regimen (regardless of age; includes use in children)
      1. Doxycycline
        1. Adult: 100 mg orally twice daily for 14 days
        2. Child: 2.2 mg/kg orally twice daily up to 100 mg (weight <45 kg or 100 lb)
      2. Precautions: Increased mortality in age <5 years old
        1. Do not hesitate to prescribe Doxycycline to a child with Ehrlichiosis (per AAP and CDC)
    2. Alternative regimens
      1. Tetracycline
      2. Rifampin
      3. Prior options included Chloramphenicol

IX. Complications: Untreated Disease

  1. Meningoencephalitis
  2. Respiratory Failure
  3. Uncontrolled Bleeding
  4. Mortality 3%

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