Dengue type-2 viruses isolated in metropolitan Bangkok during 1980 (Bangkok/80) were characterized by oligonucleotide fingerprinting, restriction enzyme (RE) mapping and antigenic analysis using monoclonal antibody probes. Of 10 isolates analysed by oligonucleotide fingerprinting, nine were very closely related, showing 72.5% to 91.4% oligonucleotide homology. One isolate (D80-141) produced a distinctly different fingerprint (55.7% to 58.0% homology) and was less related to other Bangkok/80 dengue-2 virus isolates than to a 1964 Bangkok isolate (16681). RE mapping conducted on complementary dsDNA prepared from three Bangkok/80 isolates, strain 16681 and the prototype New Guinea C strain confirmed that D80-141 was genetically distinct. On antigenic analysis, only one of 22 monoclonal antibody probes produced against representative 1980 Bangkok dengue-2 isolates, D80-100 and D80-141, was able to distinguish between these virus strains. Monoclonal antibody 47-10/10, prepared using D80-100 virus and directed at the NS1 non-structural glycoprotein, had a significantly lower (100-fold) solid phase radioimmune assay endpoint titre for D80-141 antigen than for D80-100 antigen. By the indirect immunofluorescence assay, 47-10/10 had lower antibody endpoint titres against D80-141, the NGC strain and 13 (12%) of 110 Bangkok/80 isolates than to a control antibody preparation. These results suggest that strain D80-141 represents a second minor topotype of dengue-2 which was circulating concurrently with the major endemic topotype in Bangkok in early 1980.
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