Vector

Human Monocytic Ehrlichiosis

search

Human Monocytic Ehrlichiosis, Ehrlichia chaffeensis, Ehrlichia ewingii, Ehrlichiosis, Human Ehrlichiosis

  • 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)
  • Pathophysiology
  1. Carried by Lone star tick (Amblyomma americanum)
  2. Small gram-negative organisms (Neorickettsia)
    1. Pleomorphic
    2. Obligate intracellular organisms
  3. Organisms causing Human Monocytic Ehrlichiosis
    1. Ehrlichia chaffeensis (primary cause)
    2. Ehrlichia ewingii (similar disease in immunocompromised patients and dogs)
  • Symptoms (Occur 7-10 days after Tick Bite)
  1. Common Initial Symptoms
    1. Fever
    2. Shaking chills
    3. Myalgia
    4. Headache
  2. Other symptoms
    1. Malaise
    2. Nausea and Vomiting, Anorexia
    3. Abdominal Pain
    4. Diarrhea
    5. Cough
    6. Conjunctival Injection
    7. Confusion
  • Signs
  • Rash
  1. Present in 30% of patients
  2. Involves trunk
  3. Spares hands and feet
  4. Not associated with Tick Bite site
    1. Contrast with Erythema Migrans in Lyme Disease
  • Differential Diagnosis
  1. See Tick Borne Illness
  2. Similar to Anaplasmosis presentation, and Rocky Mountain Spotted Fever Presentation (with different rash)
  • Labs
  1. Complete Blood Count
    1. Leukopenia
    2. Thrombocytopenia
  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. Ehrlichia PCR
    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
  • 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 7 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