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Points of interest:
The main species causing human disease are Babesia microti, Babesia divergens and Babesia venatorum.
It is transmitted to humans from rodents via the tick Ixodes scapularis which is the same vector that transmits anaplasmosis and Lyme disease. Coinfection with the latter two should be tested for.
Rare transmission occurs via transfusion.
Asplenia is a risk factor (and is associated with more severe disease) but is not necessary for development of disease.
It is increasingly being recognized in immunocompetent hosts.
Complications include hemolysis, cytopenias (any or all three), hemophagocytic lymphohistiocytosis, DIC, multi organ failure, splenomegaly, splenic infarct and splenic rupture. Many infections are mild and self limiting.
The intracellular forms may be confused with malaria parasites. The maltese cross, though pathognomonic, is often not seen. PCR is available but is not sensitive below 50 parasites per ml.