The Parasite: Babesia is a microscopic parasite that occurs primarily in the Northeast and upper Midwest of the United States. It has two hosts, and its life cycle begins when a Babesia-infected tick bites the first host -- generally a white-footed mouse. The parasite, in sporozite form, undergoes asexual reproduction in the mouse's blood. It is eventually transmitted to another tick during a blood meal. Babesia is transmitted to humans through tick bites (most commonly deer ticks). In rare instances, the Babesia parasite is transmitted through a transfusion of blood from a donor with a case of silent Babesiosis or by congenital transmission during pregnancy (i.e. from infected mother to baby). Once inside a human host, the parasite invades and can destroy the host's red blood cells, sometimes faster than the body can replace them.