Molecular approaches to elucidating innate and acquired immune responses to Babesia bovis, a protozoan parasite that causes persistent infection

For many vector-transmitted protozoal parasites, immunological control of a cute infection leads to a state of persistent infection during which parasi temias may cycle unnoticed in infected but otherwise clinically healthy ani mals. Achieving persistent infection is a strategy that favors parasitism, since both host and, therefore, parasite survive, and endemically infected animal populations provide a reservoir of parasites continually available f or subsequent transmission. Examples of the major economically important pr otozoan pathogens that cause persistent infection in mammals include the re lated Theileria and Babesia parasites as well as Trypanosoma species. Contr ol of acute infection and maintenance of clinical immunity against subseque nt infection are determined by the interplay of innate and acquired immune responses. This review will focus on approaches taken to gain an understand ing of the molecular basis for innate and acquired immunity against the hem oprotozoan parasite of cattle, Babesia bovis. Knowledge of mechanisms used by the parasite to survive within infected cattle from acute to persistent infection combined with definition of the correlates of protective immunity in cattle should be applicable to designing effective vaccines. (C) 2001 E lsevier Science B.V. All rights reserved.