Babesia

Babesia microti is spread by the bite of Ixodes scapularis ticks. It is endemic in Northeast and Upper Midwest states of the USA. As these ticks are small, people may not remember the tick bite. Infection may also occur by blood transfusion or as a congenital infection. Life cycle of Babesia involves two hosts - white footed mouse and tick (definitive host). During a blood meal, a Babesia-infected tick introduces sporozoites into the human host which multiply by budding within the RBCs. Clinical features include flu-like symptoms, hypotension, hemolytic anemia, jaundice, thrombocytopenia and DIC can occur. Laboratory diagnosis is done by blood smears. It shows ring forms within the RBCs. The RBCs are of normal size. Multiple rings may be seen within a single RBC. Rings of Babesia spp. have delicate cytoplasm and are often pleomorphic. Occasional classic tetrad-forms “Maltese Cross” or extracellular rings can be present. PCR or serology can 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.