Canonical correlative analyses among an enzyme-linked immunosorbent assay using synthetic peptides, an indirect fluorescent antibody test, and hematologic measurements in dogs infected with Ehrlichia canis

Background Immunoreactive tandem repeat proteins (TRPs) in amino acid sequences were identified and employed in the serologic diagnosis of canine monocytic ehrlichiosis (CME). Objectives This study evaluated using TRP19 and TRP36 synthetic protein antigens with enzyme-linked immunosorbent assays (ELISAs) and compared the results with an indirect fluorescent antibody test (IFAT) to diagnose CME in the serum of dogs with suspected CME. Methods The sera of 243 dogs that exhibited clinical and hematologic signs suggestive of CME had IFATs performed. An ELISA with synthetic TRP19 and TRP36 antigens from two E canis genotypes (USTRP36 and BrTRP36) that circulate in Brazil were also performed. Canonical correlations and chi-square tests were evaluated on the results of these tests. Results Among the 243 dogs, 179 (73.6%) were reactive at an IFAT >= 40, 167 (68.72%) reacted at the cut-off >= 160, and 149 (61.31%) reacted at >= 640. The ELISA revealed that 172 (70.8%) dogs reacted to TRP19 peptide, 163 (67.1%) reacted to USTRP36, and 114 (46.9%) reacted to BrTRP36. The canonical correlation analyses showed that the TRP19 ELISA was the most effective diagnostic method. Serum total protein levels showed strong positive correlations with the USTRP36 peptide. Qualitative analyses revealed an association between the TRP19 peptide and the presence of anemia, thrombocytopenia, and hyperproteinemia. The IFAT results at titers of >= 160 and >= 640 were associated with thrombocytopenia. Conclusions The results of this study indicated that the TRP19 peptide was an excellent antigen and that the IFAT was diagnostically important in confirming the diagnosis of CME in serum samples.