Human Granulocytic Anaplasmosis

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

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II. 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

III. Pathophysiology

  1. Transmission: Tick Borne
    1. Deer Tick Bite (Ixodes Tick)
  2. Small gram-negative organisms
    1. Pleomorphic
    2. Obligate intracellular organisms
    3. Infects Neutrophils
  3. Causative Organism (Rickettsial Disease)
    1. New Name: Anaplasma phagocytophila (Human Granulocytic Anaplasmosis or HGA)
    2. Prior Name: Ehrilichia phagocytophila (Human Granulocytic Ehrlichiosis, renamed in 2001)
    3. Similar organisms affect horses (E. equi) and dogs (E. ewingii)

IV. Risk Factors: Severe Cases

  1. Immunocompromised
  2. Immunosuppressant medications
  3. Organ transplant
  4. Cancer
  5. HIV infection
  6. Splenectomy

V. Symptoms

  1. Occurs 5-14 days after Incubation Period following Tick Bite
    1. Tick Bite recalled in up to 75% of cases
  2. Common Initial Symptoms (flu-like)
    1. Fever
    2. Shaking chills to rigors
    3. Diaphoresis
    4. Myalgias
    5. Severe Headache
    6. Fatigue
  3. Other symptoms
    1. Malaise
    2. Nausea and Vomiting, Anorexia
    3. Abdominal Pain
    4. Diarrhea
    5. Cough
    6. Confusion

VI. 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)

VII. Differential Diagnosis

  1. See Tick Borne Illness
  2. Similar to Ehrlichiosis presentation, and Rocky Mountain Spotted Fever Presentation (with different rash)
  3. Consider coinfection (Lyme Disease, Rocky Mountain Spotted Fever) carried by the same ticks

VIII. 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. Whole Blood Anaplasma PCR (37% Sensitivity)
    1. Most sensitive in first 2 weeks of infection
  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

IX. Management

  1. Antibiotic course: 7-14 days
  2. Preferred in all ages (even under age 8 years old)
    1. Doxycycline 2.3 mg/kg up to 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

X. Complications: Untreated Disease

  1. Meningoencephalitis
  2. Respiratory Failure
  3. Uncontrolled Bleeding
  4. Mortality 0.3% (contrast with 3% in Ehrlichiosis)

XI. Prognosis

  1. Severe disease and death are rare, but are more common in Immunocompromised patients

XII. Prevention

  1. See Prevention of Vector-borne Infection

XIII. Resources

  1. CDC: Anaplasmosis
    1. http://www.cdc.gov/anaplasmosis/
  2. Minnesota Department of Health
    1. http://www.health.state.mn.us/divs/idepc/diseases/anaplasmosis/hcp.html

XIV. References

  1. (2016) Sanford Guide to Antibiotics app, accessed 4/12/2016
  2. (1995) MMWR Morb Mortal Wkly Rep 44:593-5 [PubMed]
  3. Fritz (1998) Infect Dis Clin North Am 12:123-36 [PubMed]
  4. Glushko (1997) Postgrad Med 101(6):225-30 [PubMed]
  5. McQuiston (1999) Emerg Infect Dis 5:635-42 [PubMed]
  6. Pace (2020) Am Fam Physician 101(9): 530-40 [PubMed]
  7. Weinstein (1996) Am Fam Physician 54(6):1971-6 [PubMed]

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