Comparisons of some bluetongue virus isolates by plaque neutralization and relatedness tests

Seven North American bluetongue virus isolates, cloned by plaquing, and sera to five of them were reacted in a plaque neutralization test. Using a paired controls system, each virus-serum reaction was studied in terms of the regression of percent neutralization on log serum dilution. Antigen-antibody interaction terms in the analysis of effective dose estimates were used to assess the relatedness of the virus isolates. The degree of cross reactivity formed a spectrum from virtually no evidence of unrelatedness to clear antigenic differences.