Characterization of a<i>Borrelia burgdorferi</i>VlsE Invariable Region Useful in Canine Lyme Disease Serodiagnosis by Enzyme-Linked Immunosorbent Assay

Sera collected from dogs experimentally infected with Borrelia burgdorferi by tick inoculation were analyzed for an antibody response to each of the six invariable regions (IRs; i.e., IR(1) to IR(6)) of VlsE, the variable surface antigen of B. burgdorferi. Six synthetic peptides (C(1) to C(6)), which reproduced the six IR sequences were used as peptide-based, enzyme-linked immunosorbent assay (ELISA) antigens. Two IRs, IR(2) and IR(6), were found to be immunodominant. Studies with serially collected serum samples from experimentally infected dogs revealed that the antibody response to IR(6) appears earlier and is stronger than that to IR(2). Thus, the IR(6) sequence alone appeared to be sufficient for serodiagnosis. When C(6) alone was used as antigen, the peptide-based ELISA was positive in 7 of 23 dogs (30%) as early as 3 weeks postinfection. All dogs (n = 33) became strongly positive 1 or 2 weeks later, and this response persisted for the entire study, which lasted for 69 weeks. Of 55 sera submitted by veterinarians from dogs suspected of having Lyme disease, 19 were also positive by the C(6) ELISA, compared to 20 positives detected by immunoblot analysis using cultured B. burgdorferi lysates as antigen. The sensitivity of using C(2) and C(6) together for detecting specific antibody in both experimentally infected and clinically diagnosed dogs was not better than sensitivity with C(6) alone, confirming that C(6) suffices as a diagnostic probe. Moreover, the C(6) ELISA yielded 100% specificity with serum samples collected from 70 healthy dogs, 14 dogs with infections other than B. burgdorferi, and 15 animals vaccinated with either outer surface protein A, whole-spirochete vaccines, or the common puppy-vaccines. Therefore, this C(6) ELISA was both sensitive and specific for the serodiagnosis of canine Lyme disease and could be used with vaccinated dogs.