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The surface antigen 1-related sequence 2 of Neospora caninum (NcSRS2) is considered as an immunodominant antigen. In this study, the gene encoding truncated NcSRS2 (NcSRS2t) lacking an N-terminal signal peptide and C-terminal hydrophobic regions was expressed in Escherichia coli, and its diagnostic potential in an enzyme-linked immunosorbent assay (ELISA) was evaluated. ELISA could discriminate clearly between known N. caninum-positive and -negative sera from cattle. Field serum samples collected from cattle in Brazil were examined for the diagnosis of N. caninum infection using ELISA. Of the 197 samples analyzed, 64 (32.5%) samples were positive for antibodies to N. caninum. Of the 64 ELISA-positive samples, 58 (90.6%) were confirmed as positive by Western blot analysis with whole-parasite antigens. These results suggest that ELISA with recombinant NcSRS2t is an effective method for diagnosis of N. caninum infection in cattle.

The potential role of Boophilus microplus as a natural tick vector of Babesia equi and Babesia caballi in Brazilian horses was assessed using nested polymerase chain reaction (PCR)-based marker assay. B. equi merozoite-specific 218bp gene fragment was detected in almost 96% of horse blood samples, and 45.3-62.5% of females, eggs, larvae, and nymphs of B. microplus collected from 47 horses at Campo Grande in the State of Matto Grosso, Brazil. Except for the partially-fed female ticks, the B. caballi-specific 430bp gene fragment was amplified from horse blood samples, and all developmental stages. Parasite DNA from both species was detected in horse blood samples and B. microplus, with the preponderance of B. equi DNA. No DNA samples were positive solely for B. caballi parasite. Only 32% of the Giemsa-stained thin blood smears were positive for Babesia parasites, as against detection of B. equi parasite DNA in 95.7% of the blood samples by nested PCR. We have obtained molecular evidence that strengthens earlier experimental and ultrastructural studies in Brazil incriminating B. microplus as a natural vector of B. equi, and possibly of B. caballi. The detection of B. equi and B. caballi DNA in eggs and larvae of B. microplus is likewise suggestive of the possibility of both transovarial and transstadial parasite transmission in this tick vector.

Serum samples from horses in the States of Sao Paulo and Mato Grosso do Sul, Brazil were examined for diagnosis of equine piroplasmosis by both the latex agglutination test (LAT) and enzyme-linked immunosorbent assay (ELISA) with recombinant antigens. Of the 47 samples analyzed, 38 (81%) and 42 (90%) samples were positive for B. equi infection and B. caballi infection, respectively. In addition, 35 (75%) samples were positive for both B. equi and B. caballi infections. These results indicate that equine piroplasmosis is widespread and therefore a cause for serious concern in the States of Sao Paulo and Mato Grosso do Sul, Brazil.