Babesia

Snapshot

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.

Introduction

• 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

Presentation

• 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

Studies

• 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

Differential

• 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

Treatment

• Medical  
  • IV atovaquone and IV azithromycin
  • IV clindamycin and oral quinine

Complications

• 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