Utility of Borrelia burgdorferi sensu stricto C6 Peptide for Serologic Confirmation of Erythema-Free Ixodid Tick-Borne Borrelioses in Russia.

We evaluated the utility of Borrelia burgdorferi sensu stricto (Bb) peptide C6 for serologic confirmation of Ixodid Tick-Borne Borrelioses (ITBB) in Russia. Serum samples (N = 1089) were from erythema migrans (EM) (N = 327) and the EM-free (EMF) patients (N = 115); in some patients, the disease was accompanied by human granulocytic anaplasmosis or tick-borne encephalitis. The sera were investigated by multiplex phosphorescence analysis (PHOSPHAN) for IgM to Bb C6, recombinant OspC and VlsE proteins, and IgG to C6 from Bb, B. garinii (Bg), and B. afzelii (Ba). Detection of Bb C6 IgM/IgG provided effective serologic confirmation of ITBB in both EM and EMF patients early after disease onset. In the EM-free patients, however, this test needed to be supplemented with detection of VlsE IgM in convalescent-phase sera due to delay in development of the antibody responses for C6 IgG. In general, positive PHOSPHAN reactions were observed in 81.9% and 86.7% of the EM and EMF patients, respectively, as well as in 59 of 65 (90.8%) patients, whose blood contained B. burgdorferi sensu lato DNA. Additional detection of IgG to Bg C6 or Ba C6 had no significant contribution to serologic diagnosis of ITBB in both patient groups.