Review Topic
  • A 68-year-old man presents to the physician with complaints of fever, malaise, and chills for the past few weeks. He says that he and his wife recently visited New Hampshire for a summer family reunion, where they hiked in the White Mountains. His temperature is 102°F (38.9°C). Physical exam is notable for a palpable spleen. Laboratory studies are significant for a hematocrit of 30%, decreased serum haptoglobin levels, and an elevated reticulocyte count. A peripheral blood smear is obtained, and confirms the diagnosis.
  • Epidemiology
    • location
      • northeastern United States (same geography as Lyme disease)
    • risk factors
      • outdoor activities that increase exposure to ticks
  • Pathogenesis
    • transmission
      • Ixodes tick is the vector for the parasite  
        • same vector as Borrelia burgdorferi which causes Lyme disease; co-infection may occur
      • white-footed mouse is a reservoir
  • Associated conditions
    • hemolytic anemia
  • Symptoms 
    • fever
      • may be sustained or intermittent
    • chills
    • malaise
    • fatigue
    • arthralgias
    • nausea and vomiting
    • dark urine
  • Physical exam
    • typically few, if any, physical findings
    • in a minority of patients
      • jaundice
      • splenomegaly
      • hepatomegaly
      • petechiae
      • ecchymoses
  • Labs
    • complete blood count with differential
      • mild-to-severe hemolytic anemia
      • lymphopenia
      • thrombocytopenia
    • decreased serum haptoglobin levels
    • elevated reticulocyte counts
  • Histology
    • peripheral blood smear
      • Giemsa-stained or Wright-stained
        • intraerythrocytic ring forms with a central pallor
        • merozoites arranged in tetrad configuration resembling a Maltese cross (pathognomonic of babesiosis) 
  • Making the diagnosis
    • based on clinical presentation and peripheral blood smear findings
  • Malaria
    • distinguishing factor
      • visualization of Plasmodium on peripheral blood smear
  • Lyme disease
    • distinguishing factor
      • erythema migrans (bulls-eye rash)
  • Erlichiosis
    • distinguishing factor
      • southeastern and mid-Atlantic United States
  • Medical 
    • IV atovaquone and IV azithromycin
    • IV clindamycin and oral quinine
  • Severe hemolytic anemia
  • Thrombocytopenia
  • Disseminated intravascular coagulation (DIC)
  • Death
    • babesiosis can be severe or life-threatening particularly in the following groups
      • asplenic patients
      • immunocompromised patients
      • elderly

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