Prime-boost immunization with DNA followed by a recombinant vaccinia virus expressing P50 induced protective immunity against Babesia gibsoni infection in dogs.

A heterologous prime-boost immunization regime with priming DNA followed by recombinant vaccinia virus expressing relevant antigens has been shown to induce effective immune responses against several infectious pathogens. In this study, we constructed a recombinant plasmid and vaccinia virus, both of which expressed P50 of Babesia gibsoni, to investigate the immunogenicity and protective efficacy of a heterologous prime-boost immunization against canine babesiosis. The dogs immunized with the prime-boost regime developed a significantly high level of specific antibody against P50 when compared with the control groups, and the antibody level was strongly increased after a booster immunization with a recombinant vaccinia virus. The prime-boost immunization regime induced a specific IgG2 antibody response and IFN-gamma production in dogs. Two weeks after the booster immunization with a recombinant vaccinia virus expressing P50, the dogs were challenged with B. gibsoni patasites. The dogs immunized with the prime-boost regime showed partial protection, manifested as a significantly low level of parasitemia and a 2-day delay of the peak parasitemia. These results indicated that such a heterologous prime-boost immunization approach might be useful against B. gibsoni infection in dogs.