Cultivation of Babesia and Babesia-like blood parasites: agents of an emerging zoonotic disease.

Babesia and its close relatives are members of a group of organisms called piroplasms, a name which comes from their pear-shaped outlines. Long associated with blood diseases of cattle and other mammals, members of the genus Babesia have been recognized since the 1950s as infectious agents in humans. Species of this protozoan blood parasite that have routinely been isolated from mice (B. microti) or cattle (B. divergens) have also been isolated from humans. In addition to these familiar species, new isolates that resist being placed in existing taxonomic categories are the basis for rethinking their phylogenetic relationships based on sequencing data. The parasite represents a threat to the safety of the blood supply in that blood from asymptomatic humans can transmit Babesia to blood recipients. Such transmissions have occurred. The development of methods for cultivation of these organisms represents a significant opportunity to study their biology and disease potential. In addition, in vitro cultivation has provided a basis for studying immune responses of mammals to these infectious agents, with the hope of ultimately producing attenuated strains that could be used for immunizing of cattle and, perhaps, humans who live in areas of endemicity. The microaerophilous stationary phase culture technique, which uses a tissue culture medium base supplemented with appropriate serum and erythrocytes, has made it possible to obtain large numbers of parasitized erythrocytes for studying the biology of this parasite.