Theileria equi RAP-1a and RAP-1b proteins contain immunoreactive epitopes and are suitable candidates for vaccine and diagnostics development

•Extracellular and intra-erythrocytic Theileria equi merozoites express RAP-1 proteins.•RAP-1 proteins elicit antibody responses in horses during Theileria equi infection.•RAP-1 antibodies correlate with a decline in parasite load during acute and persistent T. equi infection.•The RAP-1a protein is involved in invasion of equine erythrocytes.•N- and C- termini of the RAP-1b protein do not play a role in erythrocyte invasion.