Molecular typing of Bordetella parapertussis isolates circulating in Pakistan

Although a whole-cell pertussis vaccine was introduced in Pakistan in 1980, little is known about the pertussis prevalence and circulating strains in Pakistan. The aim of this study was to analyze Bordetella parapertussis isolates circulating between 2005 and 2009 in Pakistan and to compare them with those found in other countries during different periods. A total of 59 (7.35%) B. parapertussis isolates from 802 subjects (median age, 3 years) from Pakistan, with pertussis-like symptoms were investigated. We carried out genotyping and DNA microarray analyses on these isolates and compared them with some international isolates of B. parapertussis. We found that the allele for pertactin (prn) found in strains studied from Pakistan was identical to the predominant type found in Europe. We showed that B. parapertussis isolates circulating in Pakistan are part of the same pulsed-field gel electrophoresis group to those circulating in Finland during the period of 1982-2007. Finally, microarray analysis confirmed that the isolates collected in Pakistan, were quite similar to international strains. Overall, these results confirm that B. parapertussis is extremely monomorphic. The high isolation rate of B. parapertussis (7.35%) compared to Bordetella pertussis (0.5%) may suggest that the whole-cell vaccine used in Pakistan is effective against B. pertussis (0.5% infections detected), but much less so against B. parapertussis.