Babesia microti

 

Clinical Background

Babesiosis is a zoonosis caused by an intraerythrocytic parasite of the genus Babesia.

Epidemiology

  • Prevalence
    • Found in the Northeastern U.S. coast and upper midwestern states, the same region as agents responsible for Lyme disease and human granulocytic anaplasmosis (HGE)
      • Simultaneous infections of babesiosis, Lyme disease and HGA occur at a rate of 10% of infected patients
  • Transmission
    • Tick bite (Ixodes spp)
    • Vector – in the U.S., Ixodes scapularis (prior name of Ixodes dammini ) or more commonly known as a black-legged deer tick
    • Blood transfusion (rarely)
    • For more information on causal agents, life cycle and geographic distribution, see CDC's information on Babesiosis

Organism

  • Protozoal parasite – obligate parasite of red blood cells
  • More than 100 known species – most common types are B. microti and B. divergens

Risk Factors for Severe Disease

  • Splenectomy
  • Immunosuppression

Clinical Presentation

  • Most cases of human Babesia infection are asymptomatic
  • Symptomatic patients experience fever, headache, nausea, sweats and rigors
  • Symptoms occur 1 to 6 weeks following tick bite
  • The resemblance to a fulminant malaria-like infection may complicate initial diagnosis
  • Severe cases can result in hemolytic anemia and thrombocytopenia due to fragmentation of red blood cells by the parasite, resulting in capillary blockage in the spleen, liver, kidneys and central nervous system
  • Immunocompromised patients may experience persistent or relapsing disease
  • Complications
    • Acute respiratory failure
    • Congestive heart failure
    • Renal failure

Treatment

  • Generally treated for at least 7-10 days with a combination of two medications
    • Atovaquone and azithromycin OR
    • Clindamycin and quinine (for severely ill patients)
  • Some severely ill patients may require supportive care
    • Antipyretics to reduce fever
    • Vasopressors to increase blood pressure if low
    • Blood transfusions
    • Exchange transfusions
    • Mechanical ventilation
    • Dialysis

Prevention

  • Protection of body sites from tick exposure – long sleeves and pants when in tick-prone area
  • DEET on exposed areas