Babesia microti is transmitted by the bite of Ixodes scapularis ticks. It’s endemic in the Northeast and Upper Midwest regions of the USA. Because these ticks are very small, people often don’t remember being bitten.
Infection can also occur through:
The life cycle of Babesia involves two hosts: the white-footed mouse and the tick (the definitive host). During a blood meal, an infected tick introduces sporozoites into the human host. These sporozoites then multiply by budding within red blood cells (RBCs).
Clinical features include:
Thrombocytopenia and disseminated intravascular coagulation (DIC) can also occur.
Laboratory diagnosis is made using blood smears. Findings include:
PCR or serology may be used in some cases.
Babesia sp. in a thin blood smear; note the tetrad form and ameboid trophozoite.
Babesia sp. in a thin blood smear stained with Giemsa, showing extracellular forms.