Babesia bigemina sexual stages are induced in vitro and are specifically recognized by antibodies in the midgut of infected Boophilus microplus ticks

Babesia bigemina, a causative agent of bovine babesiosis, is transmitted from one bovine to another only by infected ticks. The life cycle of B. bigemina includes a sexual phase in the tick host; however, molecules from sexual stages of any Babesia species have not been characterized. This is the first report of the induction of sexual stages of any Babesia species in vitro, free of tick antigens. Intraerythrocytic parasites were cultured in vitro for 20 It using an induction medium. Extraerythrocytic parasites were first seen 3 h post induction; elongated stages with long projections appeared at 6 h post induction and by 9 h they paired and fused to form larger stages. Round zygotes appeared 20 h post induction. Moreover, by using Percoll gradients, sexual stages were purified free of contaminating intraerythrocytic stages. Purified parasites were used to generate polyclonal antibodies, which specifically bound to antigens expressed in sexual stages induced in vitro, but not to antigens expressed in intraerythrocytic stages. Importantly, these antibodies specifically identified sexual stages from midguts of female Boophilus microplus ticks fed on infected cattle. (C) 2004 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.