Here, we identified a novel secreted
antigen designated as Babesia microti secreted
antigen 1 (BmSA1) by immunoscreening a B. microti
cDNA expression library using the sera from hamsters immunized with plasma, putatively containing secreted
antigens, from B. microti-infected hamsters.
Antibodies raised in mice immunized with recombinant BmSA1 (rBmSA1) recognized a native 33-kDa parasite
protein. An
enzyme-linked
immunosorbent assay (ELISA) of rBmSA1 detected specific
antibodies as early
as 6 and 4 days post-
infection in sera from a hamster experimentally infected with B. microti Gray strain (US type) and a mouse experimentally infected with B. microti Munich strain (rodent isolate), respectively. Moreover, a rapid immunochromatographic test (ICT) using rBmSA1 detected specific
antibodies in a hamster experimentally infected with B. microti from day 6 to at least day 270 post-
infection, which was quite consistent with the results of the ELISA. In addition, analysis of the sera involved in the first case of
human babesiosis in Japan (Kobe type) showed that specific
antibodies were detectable in the patient and the positive donor by ELISA using rBmSA1, and the ICT result was identical to the ELISA data. Taken together, these results indicated that BmSA1 could be a promising and universal target for developing both ELISA and ICT for the serodiagnosis of
human babesiosis and for an epidemiological survey of its rodent reservoir.