Abstract
ABSTRACT Pertussis caused by Bordetella pertussis, remains a public health problem worldwide, despite high vaccine coverage in infants and children in many countries. Iran has been using whole cell vaccine for the last 50 years with more than 95% vaccination rate since 1988 and has experienced pertussis resurgence in recent years. Here, we sequenced 55 B. pertussis isolates mostly collected from three provinces with the highest number of pertussis cases in Iran, including Tehran, Mazandaran, and Eastern-Azarbayjan from the period of 2008-2016. Most isolates carried ptxP3/prn2 alleles (42/55, 76%), the same genotype as isolates circulating in acellular vaccine-administrating countries. The second most frequent genotype was ptxP3/prn9 (8/55, 14%). Only three isolates (5%) were ptxP1. Phylogenetic analysis showed that Iranian ptxP3 isolates can be divided into eight clades (Clades 1-8) with no temporal association. Most of the isolates from Tehran grouped together as one distinctive clade (Clade 8) with six unique single nucleotide polymorphisms (SNPs). In addition, the prn9 isolates were grouped together as Clade 5 with 12 clade-supporting SNPs. No pertactin deficient isolates were found among the 55 Iranian isolates. Our findings suggest that there is an ongoing adaptation and evolution of B. pertussis regardless of the types of vaccine used.
Highlights
Despite high vaccine coverage in many countries, pertussis, known as whooping cough is still reported in all age groups with the highest severity in infants and young children [1,2,3]
There were only four non-ptxP3 isolates, one, IR142, harboured a ptxP4 allele, and three were ptxP1 which were further differentiated by ptxA allele into ptxP1/ ptxA1/fim2-1/fim3-1/ prn1 and ptxP1/ptxA2/fim2-1/ fim3-1/ prn1
Iran has been using whole cell vaccine (WCV) for immunization against pertussis for more than 50 years and continues to use WCV with a high WCV coverage [10]. It encountered an increase in pertussis cases since 2007 with highest number in 2013 with 1415 suspected cases per 100,000 [15]
Summary
Despite high vaccine coverage in many countries, pertussis, known as whooping cough is still reported in all age groups with the highest severity in infants and young children [1,2,3]. PtxP3, the pertussis toxin (Ptx) promoter allele has been shown to be associated with higher virulence [5] and ptxP3 isolates have a better fitness in animal studies [8]. The introduction of PCR based diagnosis, incomplete vaccination and the new guidelines and policies implemented in 2009 by Iran Centre for Communicable Disease Control that all suspected and confirmed cases must be notified and samples must be sent to the reference laboratory may have contributed to the increased number of reported pertussis cases in Iran [16]
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