Cattle immunized with a recombinant merozoite surface antigen-1 molecu
le (MSA-1) produced high-titered antibody that reacted with the surfac
e of the parasite and neutralized merozoite infectivity in vitro. Howe
ver, recombinant MSA-1 immunization did not confer protection against
challenge with virulent Babesia bovis. These results indicate that ant
ibody-mediated neutralization of merozoite infectivity in vitro, at le
ast for MSA-1-specific antibody, does not reflect in vivo protective i
mmunity to babesiosis.