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Human Granulocytic Anaplasmosis

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Human Granulocytic Anaplasmosis, HGA, Anaplasma phagocytophila, Human Granulocytic Ehrlichiosis, Ehrlichia equi, Ehrlichia phagocytophila, Human Anaplasmosis, Anaplasmosis

  • Epidemiology
  1. Incidence: 1832 reported cases in U.S. in 2014
  2. Majority of cases occur April to September
  3. Tick Carriers
    1. Deer Tick (Ixodes Scapularis)
    2. Dog tick (Dermacentor variabilis)
  4. United States endemic areas (similar distribution to Lyme Disease)
    1. Upper Midwest including. Minnesota
    2. Wyoming
    3. Northeast including New York
  • Pathophysiology
  1. Transmission: Tick Borne
    1. Deer Tick Bite (Ixodes Tick)
  2. Small gram-negative organisms
    1. Pleomorphic
    2. Obligate intracellular organisms
  3. Causative Organism (Rickettsial Disease)
    1. New Name: Anaplasma phagocytophila (Human Granulocytic Anaplasmosis or HGA)
    2. Prior Name: Ehrilichia phagocytophila (Human Granulocytic Ehrlichiosis)
    3. Similar organisms affect horses (E. equi) and dogs (E. ewingii)
  • Symptoms
  1. Occurs 7-10 days after Tick Bite
  2. Common Initial Symptoms
    1. Fever
    2. Shaking chills
    3. Myalgias
    4. Severe Headache
  3. Other symptoms
    1. Malaise
    2. Nausea and Vomiting, Anorexia
    3. Abdominal Pain
    4. Diarrhea
    5. Cough
    6. Confusion
  • Signs
  • Rash
  1. Occurs in <10% of patients (contrast with >30% in Ehrlichiosis)
  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 (unlike Erythema Migrans)
  • Differential Diagnosis
  1. See Tick Borne Illness
  2. Similar to Ehrlichiosis presentation, and Rocky Mountain Spotted Fever Presentation (with different rash)
  • Labs
  1. Complete Blood Count
    1. Leukopenia
    2. Thrombocytopenia (unique to Anaplasmosis compared with Babesia and Lymes Disease)
    3. Mild transient Anemia
  2. Liver transaminases increased
    1. Aspartate Aminotransferase (AST) increased
    2. Alanine Aminotransferase (ALT) increased
  3. Anaplasma PCR (37% Sensitivity)
  4. Anaplasma Serology
    1. Positive two weeks after onset
    2. Used for confirmation, not for diagnosis
    3. Anticipate a fourfold rise in Antibody titers on re-testing at 3-4 weeks
      1. Minimum peak 1:64
      2. Maximum peak 1:128 or higher dilution
  5. Other variably present laboratory findings
    1. Increased Erythrocyte Sedimentation Rate (ESR)
    2. Increased Blood Urea Nitrogen (BUN)
    3. Increased Serum Creatinine
  • Management
  1. Antibiotic course: 10-14 days
  2. Preferred
    1. Doxycycline 100 mg oral or IV twice daily for 7 to 14 days
  3. Alternatives
    1. Tetracycline 500 mg orally four times daily for 7 to 14 days
    2. Rifampin 10 mg/kg up to 600 mg twice daily for 5 to 7 days
      1. May be used in pregnancy, but increasing resistance
  • Complications
  • Untreated Disease
  1. Meningoencephalitis
  2. Respiratory Failure
  3. Uncontrolled Bleeding
  4. Mortality <1% (contrast with 3% in Ehrlichiosis)