Characterization of a Borrelia burgdorferi 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 s ix invariable regions (IRs; i.e., IR1 to IR6) of VlsE, the variable surface antigen of B. burgdorferi. Six synthetic peptides (C-1 to C-6), which repr oduced the six IR sequences were used as peptide-based, enzyme-linked immun osorbent assay (ELISA) antigens. Two IRs, IR2 and IR6, were found to be imm unodominant. Studies with serially collected serum samples from experimenta lly infected dogs revealed that the antibody response to IR6 appears earlie r and is stronger than that to IR2. Thus, the IR6 sequence alone appeared t o 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 late r, and this response persisted for the entire study, which lasted for 69 we eks. Of 55 sera submitted by veterinarians from dogs suspected of having Ly me disease, 19 were also positive by the C-6 ELISA, compared to 20 positive s detected by immunoblot analysis using cultured B. burgdorferi lysates as antigen. The sensitivity of using C-2 and C-6 together for detecting specif ic antibody in both experimentally infected and clinically diagnosed dogs w as 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 wi th serum samples collected from 70 healthy dogs, 14 dogs with infections ot her than B. burgdorferi, and 15 animals vaccinated with either outer surfac e protein A, whole-spirochete vaccines, or the common puppy-vaccines. There fore, this C-6 ELISA was both sensitive and specific for the serodiagnosis of canine Lyme disease and could be used with vaccinated dogs.