Emerging perspectives in the research of bovine babesiosis and anaplasmosis.

The Babesia bovis and B. bigemina apicomplexan protozoa in conjunction with the rickettsia Anaplasma marginale are intraerythrocytic pathogens that are responsible for the most prevalent and costly tick borne diseases (TBD's) of cattle worldwide. These organisms are historically associated as they can cause clinically related hemolytic diseases in cattle, are all transmitted by Rhiphicephallus (Boophilus) ticks, and share an uncanny ability to evade the immune systems of the vertebrate hosts, causing persistent disease. In addition, acute babesiosis and anaplasmosis can be prevented quite effectively by combining tick control and vaccination with living attenuated organisms. However these methods of control have numerous limitations and improved approaches are needed. Importantly, immunizations of cattle with inactivated experimental Babesia and Anaplasma vaccines can elicit variable degrees of protection, indicating the feasibility for the development of inactivated or subunit vaccines. A new research toolbox that includes full genome sequencing combined with the improved ability to genetically modify the organisms is enhancing our understanding of their biology. An emerging paradigm is the use of recently developed Babesia and Anaplasma transfection methods for functional gene characterizations and for vaccine development. Promising recently identified subunit vaccine candidates are also emerging, including babesial proteases, putative rhoptry, microneme, and sexual stage antigens, as well as subdominant, conserved, A. marginale outer membrane major surface proteins. However, significant knowledge gaps on the role of key parasite molecules involved in cell invasion, adhesion, asexual and sexual reproduction, tick transmission, and evasion of the immune system, remain. A better understanding of the biology of these organisms and the protective immune responses will positively contribute toward the goal of developing improved immunological and pharmacological interventions against these elusive pathogens that are responsible for the most devastating TBD's of cattle. Importantly, the currently available research toolbox provides basic research instruments for helping close current knowledge gaps which will aid the design and production of effective vaccines and alternative pharmacological interventions.