II. Epidemiology

  1. Incidence: 200 to 300 cases per year
  2. Region: Most common in Rocky Mountains

III. Pathophysiology

  1. Cause: RNA orbivirus
  2. Transmission
    1. Dermacentor andersoni (wood Tick Bite)
    2. Infected Blood Transfusion

IV. Risk Factors for severe infection

  1. Asplenic patients
  2. Immunocompromised patients

V. Symptoms: Influenza-like illness

  1. Timing
    1. Onset 3-5 days after inoculation (Tick Bite)
    2. Symptom duration 7-10 days
  2. Pharyngitis
  3. Biphasic high fever (saddle-back fever)
  4. Meningitis
  5. Rash
  6. Conjunctivitis
  7. Photophobia
  8. Retro-orbital Headache

VI. Diagnosis

  1. Serology
    1. Confirms diagnosis at 2-4 weeks
  2. PCR
    1. Reverse-transcriptase PCR can make the diagnosis within days of onset

VII. Differential Diagnosis

VIII. Labs

  1. Blood smear with immunofluorescent stain for virus
  2. Complete Blood Count
    1. Leukopenia
    2. Thrombocytopenia

IX. Management

  1. Symptomatic (self-limited, no specific treatment exists)

X. Complications: Uncommon

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