Babesia sp. life cycle. Babesia sp. life cycle. Sporozoite-carrying ticks infect a mammalian host while taking a blood meal. Sporozoites enter erythrocytes (RBCs) and reproduce through asynchronous binary fission, resulting in two, or sometimes four, merozoites. Once present in a reservoir host (for B. microti, the reservoir is the white-footed mouse), parasites will develop into male and female gametes. When an ixodid tick feeds upon a competent reservoir, blood-stage gametes are introduced into the gut, where these gametes are fertilized to become zygotes. Zygotes enter the tick salivary gland and undergo a sporogonic cycle, forming infectious sporozoites. Humans are generally an intermediate host of Babesia species, although blood transfusion transmission does occur. Dogs are intermediate hosts, much like humans, although they may have a domestic reservoir role in the human transmission of the newly emerging species Babesia conradae. Kevin J. Esch, and Christine A. Petersen Clin. Microbiol. Rev. 2013; doi:10.1128/CMR.00067-12