Babesiosis is an infectious disease caused by parasites which invade and burst red blood cells open. In the United States, particularly along the northeastern seaboard, babesiosis is caused by Babesia microti. The ring form is the most common (left panels) whereas tetrads are rare (right panels). Babesia microti is carried by white-footed mice, and is transmitted from one mouse to another by the deer tick. Unfortunately, deer ticks feed on people, thereby transmitting the parasite. Unlike Lyme disease, its fellow traveler, babesiosis can be life-threatening. The infection also can be acquired through transfusion of contaminated blood products.