Babesiosis is transmitted to humans through the blood meal of Ixodes ticks, the same vector as for Lyme disease and human granulocytic anaplasmosis.
Peak transmission occurs from May to September in upper midwestern and northeastern US. The disease is rare in other countries.
Transfusion-related transmission is emerging as an important secondary mode of transmission; therefore, transmission can occur anywhere and at any time of year.
Usually asymptomatic or presents as a mild viral-type illness in young and healthy people. May cause more serious disease or be fatal in asplenic or immunocompromised patients and in older people.
Diagnosis is made by visualization of parasites on a peripheral blood smear or by molecular testing.
Management depends on the severity of disease and includes observation and monitoring, antimicrobials, and/or exchange transfusion.
Babesiosis is a tick-borne zoonotic disease typically characterized by fever, hemolysis, and hemoglobinuria. It is most frequently caused by the intraerythrocytic parasite Babesia microti, commonly transmitted through the bite of Ixodes ticks (deer ticks).
History and exam
Other diagnostic factors
- constitutional symptoms
- petechiae, splinter hemorrhages, or ecchymoses
- dark urine
- conjunctival injection
- sore throat
- residence in or travel to an endemic region
- exposure to Ixodes scapularis ticks
- blood transfusion
- age >50 years
- Lyme disease
- human granulocytic anaplasmosis
- maternal infection during pregnancy
1st investigations to order
- peripheral blood smear (Giemsa or Wright stained)
- polymerase chain reaction for babesial DNA
- serum creatinine and blood urea nitrogen (BUN)
- ELISA and/or immunofluorescence assay for Lyme disease
- polymerase chain reaction and/or immunofluorescence assay or buffy coat smear for human granulocytic anaplasmosis
Investigations to consider
- indirect immunofluorescence antibody assay for Babesia microti
- IgG/IgM immunoblot for Lyme disease
- HIV serology
asymptomatic documented infection
mild to moderate disease
acute severe disease
recurrent or refractory disease
- Lyme disease
- Human granulocytic anaplasmosis
- Rocky Mountain spotted fever
- 2020 Guideline on diagnosis and management of babesiosis
- 2020 guideline on diagnosis and management of Babesiosis
Malaria preventionMore Patient leaflets
- Log in or subscribe to access all of BMJ Best Practice
Use of this content is subject to our disclaimer