Immunodiagnosis of Ehrlichia canis infection with recombinant proteins

Ehrlichia canis causes a potentially fatal rickettsial disease of dogs that requires rapid and accurate diagnosis in order to initiate appropriate the rapy leading to a favorable prognosis. We recently reported the cloning of two immunoreactive E. canis proteins, P28 and P140, that were applicable fo r serodiagnosis of the disease. In the present study we cloned a new immuno reactive E. canis surface protein gene of 1,170 bp, which encodes a protein with a predicted molecular mass of 42.6 kDa (P43). The P43 gene was not de tected in E. chaffeensis DNA by Southern blot, and antisera against recombi nant P43 (rP43) did not react with E. chaffeensis as detected by indirect f luorescent antibody (IFA) assay. Forty-two dogs exhibiting signs and/or hem atologic abnormalities associated with canine ehrlichiosis were tested by I FA assay and by recombinant Western immunoblot. hmong the 22 samples that w ere IFA positive for E. canis, 100% reacted with rP43, 96% reacted with rP2 8, and 96% reacted with rP140. The specificity of the recombinant proteins compared to the IFAs was 96% for rP28, 88% for P43 and 63% for P140. The re sults of this study demonstrate that the rP43 and rP28 are sensitive and re liable serodiagnostic antigens for E. canis infections.