DYNAMICS OF THE POPULATION-STRUCTURE OF BORDETELLA-PERTUSSIS AS MEASURED BY IS1002-ASSOCIATED RFLP - COMPARISON OF PREVACCINATION AND POSTVACCINATION STRAINS AND GLOBAL DISTRIBUTION

The effect of temporal and geographic factors on the population struct ure of Bordetella pertussis was studied using IS1002-based RFLP analys is. Among the 106 strains analysed, 36 different RFLP types were obser ved. For the Dutch strains, there was evidence for a shift in the popu lation structure in time since the majority of strains were found in d ifferent families of related strains in successive periods. Most prono unced were the differences observed between 1950-1954 and later period s. This difference may have been caused by the introduction of the who le-cell vaccine in 1953, resulting in the expansion of strains which a re less affected by vaccine-induced immunity. Strains with RFLP types identical to the vaccine strains were observed in the period 1950-1954 , but not later, suggesting a decreased frequency of such strains due to vaccination, Analysis of strains from the 1994 Dutch pertussis epid emic revealed that 71% of the strains belonged to two RFLP types, indi cating that pertussis epidemics are caused by clonal expansion. IS1002 -based RFLP analysis of strains from different countries suggested a p artial geographic isolation of a. pertussis populations. One RFLP type was found to have a wide distribution in time and in space.