Virulence Factors Variation Among Bordetella Pertussis Isolates in Iran

∗ Corresponding author: Pertussis Reference Laboratory, Department of Bacteriology and Microbiology Research Center, Pasteur Institute of Iran. Email: [email protected] ertussis or whooping cough, caused by Bordetella pertussis, is one of the important vaccine preventable diseases. Pertussis vaccination is recommended as a part of routine childhood immunization. The whole cell pertussis vaccine (WCV) combined with tetanus and diphtheria toxoids (DTP) was introduced in the 1950s in many countries (1-3). A new form of vaccine called "Acellular vaccine (ACV)" that contained a limited number of defined proteins, was introduced in many developed countries using this vaccine vaccinating their populations for nearly 14 years. This vaccine replaced WCV to avoid the side effects of the latter vaccine in some countries (4). Although the incidence of pertussis was successfully reduced after the introduction of both types of vaccines, the disease is still endemic and the resurgence of pertussis has been revealed in many countries even with high vaccination coverage (5-8). It has been suggested that among the several reasons of this reemergence (9), genetic diversity in virulence factors is one of the major causes that has affected vaccine efficacy (10-13). Pertussis toxin (Ptx) and pertactin (Prn) are two virulence factors used in ACV vaccine which confer protective immunity in animals and humans (14). The gene encoding fimbriae is the other virulence gene which is also subject to variation due to mutation. B. pertussis strains contain Fim2 and/or Fim3 fimbriae serotypes. Two and four alleles of fim2 and fim3 genes have been identified up to now (15). Packard et al. in 2004 showed that as a variation within cyaA was extremely rare, it may be suitable for inclusion in ACVs (16). Based on studies of B. pertussis strains variation, first from the Netherlands (12), it was postulated that the antigenic divergence between vaccine strains and clinical isolates may have contributed to the resurgence of pertussis (17). Previous publications demonstrated that nonvaccine types of Ptx, Prn and Fim3 (immune factors) replaced the vaccine types in later years and the isolates collected in the vaccination period appeared to be genotypically different from the vaccine strains in use (18-19). Despite the 99% coverage of pertussis vaccination in Iran, like other countries we also observed an increase in pertussis rate in our country since 2004. The incidence of pertussis was 98, 125 and 650 cases in 2004, 2005 and 2011 (20-22). The P Submmited 15 December 2014; Accepted 23 February 2015; Published 24 March 2015