Targeting Subdominant Rhoptry-associated Proteins of Babesia Bovis in a Subunit Vaccine to Protect Cattle Against Bovine Babesiosis

The immunodominant B. bovis rhoptry associated protein-1 (RAP-1) is a leading vaccine candidate that is expressed at least in B. bovis merozoites and sporozoites. The ability of the B. bovis RAP-1 to bind to the erythrocyte surface and the presence of RAP-1 neutralization sensitive epitopes leads to the hypothesis that RAP-1 is involved in erythrocyte invasion by the parasites. However, we previously demonstrated that strong humoral and cellular responses in vaccinated cattle with RAP-1 were unable to induce protection against challenge with virulent B. bovis. Expression of a recently identified subdominant and neutralization sensitive RAP-1 Related Antigen (RRA) in B. bovis merozoites that might function as a RAP-1 substitute is a potential explanation for the lack of protection using RAP-1 as an immunogen. Additionally, subdominant antigens like RRA may be reasonable candidates for developing vaccines which could potentially elicit a neutralizing antibody response in vivo. the goal of this project is to develop a subunit vaccine containing RAP-1 NT/RRA subdominant domains fused with the molecular adjuvant Flic to protect cattle against acute bovine babesiosis.