Immunochromatographic assay of Babesia caballi and Babesia equi laveran 1901 (Theileria equi Mehlhorn and Schein, 1998) (Phylum aplcomplexa) infection in Philippine horses correlated with parasite detection in blood smears

Sera collected from 71 slaughtered and 33 racing horses were assayed for Babesia spp. infection using immunochromatographic (ICT) assay. The 1CT strips which were developed at the National Research Center for Protozoan Diseases (NRCPD), Obihiro University, Hokkaido, Japan contained a recombinant B. caballi 48-kDa rhoptry protein (rBc48) and a recombinant truncated B. equi merozoite antigen 2 (rEMA-2t) for the detection of anti-horse Babesia spp. antibodies. The 63 seropositive blood samples consisted of 41(57.7%) and 22 (66.7%) cases in slaughtered and racing horses, respectively. Twelve sera (19.0%) reacted with both B. caballi and B. equi antigens, 45 sera (71.0%) reacted with rBc48 antigen only, and six sera (10.0%) were positive for B. equi antibodies only. Babesia caballi infection accounted for 90.5% cases. Infection with B. caballi and/or B. equi confirmed in Giemsa-stained blood smears prepared from racing horse samples only revealed 22 (66.7%) seropositive cases. Paired pear or crescent-shaped merozoites (0.5-1.25 μm), characteristic of B. caballi were observed in 20 blood smears, while only two seropositive cases revealed the presence of both B. caballi and the Maltese cross or tetrad-shaped merozoites (0.62-0.95 μm) generally associated with Theileria sp. (B. equi) parasite. To our knowledge, this is the first immunochromatographic assay of equine babesiosis in the Philippines validated by the detection of specific etiologic agent(s) in blood smears