Genetic diversity of ospC in a local population of Borrelia burgdorferi sensu stricto

The outer surface protein, OspC, is highly variable in Borrelia burgdorferi sensu stricto, the agent of Lyme disease. We have shown that even within a single population OspC is highly variable. The variation of ospA and ospC in the 40 infected deer ticks collected from a single site on Shelter Islan d, New York, was determined using PCR-SSCP. There is very strong apparent l inkage disequilibrium between ospA and ospC alleles, even though they are l ocated on separate plasmids. Thirteen discernible SSCP mobility classes for ospC were identified and the DNA sequence for each was determined. These s equences, combined with 40 GenBank sequences, allow us to define 19 major o spC groups. Sequences within a major ospC group are, on average, <1% differ ent from each other, while sequences between major ospC groups are, on aver age, similar to 20% different. The tick sample contains 11 major ospC group s, GenBank contains 16 groups, with 8 groups found in both samples. Thus, t he ospC variation within a local population is almost as great as die varia tion of a similar-sized sample of the entire species, The Ewens-Watterson-S latkin test of allele frequency showed significant deviation from the neutr al expectation, indicating balancing selection for these major ospC groups. The variation represented by major ospC groups needs to be considered if t he OspC protein is to be used as a serodiagnostic antigen or a vaccine.