Babesiosis

Abstract Babesia spp. are protozoan parasites defining separate lineages in the Apicomplexa phylum and phylogenetically closely related to Theileria , and less closely to Plasmodium species. These parasites are transmitted primarily by ticks to a wide range of domestic and wild animals as well as humans, where they develop within the host red blood cells to cause the pathological symptoms associated with babesiosis. The widespread distribution of these parasites throughout the world, their recognition as emerging pathogens and the major economic and health impacts of babesiosis have stimulated major research efforts to understand the basic biology, pathogenesis, evolution and transmission patterns of these organisms. Key Concepts Babesia spp. parasites are the causative agents of babesiosis in wild and domestic animals, as well as humans. Babesia spp. are transmitted by ticks to mammals and birds, and reproduce asexually within host red blood cells. Babesiosis has major health and economic impacts. There are over 100 species of Babesia parasites, with several known to cause disease in humans. Babesia spp. belong to at least two distinct branches, with one capable of transovarial transmission and the other only of transstadial transmission.