Babesiosis is an intraerythrocytic protozoan infection, mainly Babesia microti in North America, transmitted by Ixodes ticks; B. divergens, B. venatorum, and B. duncani cause disease in Europe and the western United States.

Also transmitted by blood transfusion, organ transplantation, and congenitally.
Severe disease risk: age over 50, asplenia, immunosuppression (HIV, rituximab, malignancy), and chronic cardiopulmonary disease.
Often co-infection with Borrelia burgdorferi and Anaplasma.
Mortality 5 to 10% in hospitalised patients (higher in B. divergens and immunocompromised).

Blood smear (Giemsa) showing intraerythrocytic ring forms and tetrads ("Maltese cross"); parasitaemia percentage guides severity.
PCR (more sensitive), and serology (IFA, IgG titre of 1:64 or above) for exposure.
Blood count (haemolysis: low haemoglobin, raised LDH and bilirubin, low haptoglobin, reticulocytosis), liver and renal function.
Test for co-infections (Lyme, anaplasmosis).
Exclude malaria (travel history; B. microti may resemble Plasmodium falciparum rings).

Mild to moderate disease (7 to 10 days): atovaquone 750 mg orally every 12 hours plus azithromycin 500 to 1000 mg on day 1 then 250 to 500 mg daily.
Severe disease (parasitaemia above 4%, hypoxaemia, organ dysfunction): clindamycin 600 mg IV every 8 hours plus quinine 650 mg orally every 8 hours; switch to oral regimen as improved.
Exchange transfusion for parasitaemia over 10%, severe haemolysis (haemoglobin under 10 g/dL), or organ dysfunction (pulmonary, renal, hepatic, or DIC).
Immunocompromised patients: at least 6 weeks of treatment, including 2 weeks after parasite clearance (negative smears), with repeated PCR to monitor.
Supportive care in ICU, red cell transfusion, and treatment of ARDS or renal failure.
Tick avoidance, early tick removal, and screening of blood donors in endemic areas.

Babesiosis

Overview

Clinical Features

Diagnosis

Management