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

Epidemiology

• Prevalence
  • Found in the Northeastern U.S. coast, the same region as agents responsible for Lyme disease and human granulocytic ehrlichiosis (HGE)
    • Simultaneous infections of babesiosis, Lyme disease and HGE occur at a rate of 10%
• Transmission
  • Tick bite (Ixodes)
  • Vector - Ixodesdammini, Ixodesscapularis or black-legged deer tick)
    • Parasite is transmitted to humans via a bite from a parasite-infected tick
  • Blood transfusion (rarely)
  • Refer to Babesia topic at www.arupconsult.com for the Babesia microti life cycle diagram

Organism

• Protozoal parasite
• 100 existing 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 fulminating 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

Treatment

• Usually only required in severe disease

Diagnosis

• Laboratory testing
  • Giemsa-stained blood films (in patients from endemic areas)
    • Diagnostic if parasites noted
    • Relatively insensitive due to low level parasitemia in most patients
  • IFA testing
    • High sensitivity and specificity in Babesia detection
    • Test of choice for laboratory diagnosis
    • Rises 2-4 weeks after infection and wanes at 6-12 months

Differential Diagnosis

• Malaria
• Lyme disease
• Rickettsial disease
• Ehrlichiosis
• Colorado tick fever
• Human granulocytic anaplasmosis (HGA)
• Brucellosis