Surveillance of Circulating Bordetella pertussis Strains in Europe during 1998 to 2015

Pertussis vaccines, epidemiology and evolution

Pertussis, which is caused by Bordetella pertussis, has plagued humans for at least 800 years, is highly infectious and can be fatal in the unvaccinated, especially very young infants. Although the rollout of whole-cell pertussis (wP) vaccines in the 1940s and 1950s was associated with a drastic drop in incidence, concerns regarding the reactogenicity of wP vaccines led to the development of a new generation of safer, acellular (aP) vaccines that have been adopted mainly in high-income countries. Over the past 20 years, some countries that boast high aP coverage have experienced a resurgence in pertussis, which has led to substantial debate over the basic immunology, epidemiology and evolutionary biology of the bacterium. Controversy surrounds the duration of natural immunity and vaccine-derived immunity, the ability of vaccines to prevent transmission and severe disease, and the impact of evolution on evading vaccine immunity. Resolving these issues is made challenging by incomplete detection of pertussis cases, the absence of a serological marker of immunity, modest sequencing of the bacterial genome and heterogeneity in diagnostic methods of surveillance. In this Review, we lay out the complexities of contemporary pertussis and, where possible, propose a parsimonious explanation for apparently incongruous observations.

Bordetella pertussis isolates in Finland after acellular vaccination: serotype change and biofilm formation

OBJECTIVES

In Finland, whole cell pertussis vaccine (wP) was introduced in 1952 and was replaced by acellular pertussis vaccine (aP) without fimbrial (FIM) antigen in 2005. We aimed to analyse the changes in serotypes of circulating Bordetella pertussis before and after acellular vaccination and to explore the relationship between biofilm formation and serotype diversity after the introduction of aP vaccine.

METHODS

Serotyping of 1399 B. pertussis isolates collected at the Finnish National Reference Laboratory for Pertussis and Diphtheria in Turku, Finland, from 1974 to 2023 was performed by slide agglutination or indirect ELISA. Of 278 isolates collected after 2005, 53 were selected, genotyped for fim3 and fim2 alleles, and tested for biofilm formation. The selection criteria included maintaining a relatively equal distribution of isolates per time interval, ensuring approximately a 50:50 ratio of FIM2 (N = 26) and FIM3 (N = 27) serotypes. The reference strain Tohama I was used as a control.

RESULTS

During the wP era, the majority of circulating B. pertussis exhibited the FIM2 serotype. However, FIM3 strains have appeared since 1999 and become prevalent. After the implementation of aP vaccines, the distribution of serotypes has exhibited substantial variability. FIM3 isolates displayed an enhanced biofilm formation compared to FIM2 isolates (Geometric mean value (95% CI): 0.90 (0.79-1.03) vs. 0.75 (0.65-0.85); p < 0.05). Of the 27 FIM3 isolates, 8 harboured fim3-1 and 19 fim3-2 alleles. FIM3 isolates with fim3-2 allele were significantly associated with increased biofilm formation when compared to those with fim3-1 (1.07 (0.96-1.19) vs. 0.61 (0.52-0.72); p < 0.0001).

CONCLUSION

Following the implementation of aP vaccines, the distribution of serotypes in Finland has exhibited substantial variability. FIM3 isolates with the fim3-2 allele displayed an enhanced biofilm formation capability compared to FIM2 isolates.

Whole-Genome Analysis of Bordetella pertussis MT27 Isolates from School-Associated Outbreaks: Single-Nucleotide Polymorphism Diversity and Threshold of the Outbreak Strains

Bordetella pertussis, the causative agent of whooping cough, can cause pertussis outbreaks in humans, especially in school-aged children. Here, we performed whole-genome sequencing of 51 B. pertussis isolates (epidemic strain MT27) collected from patients infected during 6 school-associated outbreaks lasting less than 4 months. We compared their genetic diversity with that of 28 sporadic isolates (non-outbreak MT27 isolates) based on single-nucleotide polymorphisms (SNPs). Our temporal SNP diversity analysis revealed a mean SNP accumulation rate (time-weighted average) of 0.21 SNPs/genome/year during the outbreaks. The outbreak isolates showed a mean of 0.74 SNP differences (median, 0; range, 0 to 5) between 238 isolate pairs, whereas the sporadic isolates had a mean of 16.12 SNP differences (median, 17; range 0 to 36) between 378 isolate pairs. A low SNP diversity was observed in the outbreak isolates. Receiver operating characteristic analysis demonstrated that the optimal cutoff value to distinguish between the outbreak and sporadic isolates was 3 SNPs (Youden's index of 0.90 with a true-positive rate of 0.97 and a false-positive rate of 0.07). Based on these results, we propose an epidemiological threshold of ≤3 SNPs per genome as a reliable marker of B. pertussis strain identity during pertussis outbreaks that span less than 4 months. IMPORTANCE Bordetella pertussis is a highly infectious bacterium that easily causes pertussis outbreaks in humans, especially in school-aged children. In detection and investigation of outbreaks, excluding non-outbreak isolates is important for understanding the bacterial transmission routes. Currently, whole-genome sequencing is widely used for outbreak investigations, and the genetic relatedness of outbreak isolates is assessed based on differences in the number of single-nucleotide polymorphisms (SNPs) in the genomes of different isolates. The optimal SNP threshold defining strain identity has been proposed for many bacterial pathogens, but not for B. pertussis. In this study, we performed whole-genome sequencing of 51 B. pertussis outbreak isolates and identified a genetic threshold of ≤3 SNPs per genome as a marker defining the strain identity during pertussis outbreaks. This study provides a useful marker for identifying and analyzing pertussis outbreaks and can serve as a basis for future epidemiological studies on pertussis.

Macrolide Resistance in Bordetella pertussis: Current Situation and Future Challenges

Pertussis is a highly contagious respiratory infection caused by Bordetella pertussis bacterium. The mainstay of treatment is macrolide antibiotics that reduce transmissibility, shorten the duration of symptoms and decrease mortality in infants. Recently, the macrolide resistance of B. pertussis has been reported globally but is especially widespread in mainland China. In this review, we aim to summarise the current understanding of the epidemiology, resistance mechanisms and clinical implications of B. pertussis macrolide resistance. Since the first appearance of macrolide-resistant B. pertussis in Arizona, USA, in 1994, only sporadic cases have been reported outside China. In certain parts of China, on the other hand, up to 70-100% of the recent clinical isolates have been found to be macrolide resistant. Reasons for macrolide resistance being centred upon China during the last decade can only be speculated on, but the dominant B. pertussis lineage is different between China and most of the high-income countries. It seems evident that efforts to increase awareness, guide molecular epidemiological surveillance and carry out systematic screening of B. pertussis positive samples for macrolide resistance should be implemented globally. In addition, practices to improve the clinical care of infants with pertussis caused by resistant strains should be studied vigorously.

A Cross-Sectional Study Revealing the Emergence of Erythromycin-Resistant Bordetella pertussis Carrying ptxP3 Alleles in China

Background

Previous limited studies have identified that Bordetella pertussis (B. pertussis) isolates circulating in China possess distinct molecular features and high rates of erythromycin-resistance (ER). Their evolution and potential impact on the prevention and control of global pertussis are worthy of attention.

Methods

The present cross-sectional study involved 311 non-duplicate and unrelated B. pertussis strains isolated from Chinese children from 2017 to 2019. Their antimicrobial susceptibilities were assessed using both E-test strips and Kirby-Bauer (KB) disk diffusion methods. Seven virulence-related genes (ptxA, ptxC, ptxP, prn, fim2, fim3, and tcfA2) and the A2047G mutation in the 23S rRNA gene were detected by PCR. Based on the susceptibilities and genotypes, 50 isolates were selected for multi-locus variable-number tandem-repeat analysis (MLVA) typing and whole-genome sequencing.

Results

A total of 311 B. pertussis strains were isolated from children with a median age of 4 months (interquartile range: 2–9 months). Strains carrying the ptxP1 allele were more frequent (84.9%, 264/311), were always ER (except for one strain), and were mainly related to ptxA1/ptxC1/prn1 alleles (99.6%, 263/264). The remaining 47 (15.1%) strains carried the ptxP3 allele, mainly harboring the ptxA1/ptxC2/prn2 alleles (93.6%, 44/47), and were sensitive to erythromycin (except for two strains). The two ER-ptxP3 isolates were first identified in China, belonged to MT27 and MT28 according to MLVA, and were classified into sub-lineage IVd by phylogenetic analysis of their genome sequences. This sub-lineage also includes many strains carrying the ptxP3 allele spreading in developed countries. For each tested antimicrobial, the susceptibilities judged by KB disks were consistent with those determined by E-test strips.

Conclusion

The present results reveal that B. pertussis strains with the ptxP1-ER profile still dominate in China, and a few strains carrying the ptxP3 allele have acquired the A2047G mutation in the 23S rRNA gene and the ER phenotype. The surveillance of the drug susceptibility of B. pertussis is necessary for all countries, and the KB disk method can be adopted as a screening test.

Evolution of Bordetella pertussis in the acellular vaccine era in Norway, 1996 to 2019

We described the population structure of Bordetella pertussis (B. pertussis) in Norway from 1996 to 2019 and determined if there were evolutionary shifts and whether these correlated with changes in the childhood immunization program. We selected 180 B. pertussis isolates, 22 from the whole cell vaccine (WCV) era (1996-1997) and 158 from the acellular vaccine (ACV) era (1998-2019). We conducted whole genome sequencing and determined the distribution and frequency of allelic variants and temporal changes of ACV genes. Norwegian B. pertussis isolates were evenly distributed across a phylogenetic tree that included global strains. We identified seven different allelic profiles of ACV genes (A-F), in which profiles A1, A2, and B dominated (89%), all having pertussis toxin (ptxA) allele 1, pertussis toxin promoter (ptxP) allele 3, and pertactin (prn) allele 2 present. Isolates with ptxP1 and prn1 were not detected after 2007, whereas the prn2 allele likely emerged prior to 1972, and ptxP3 before the early 1980s. Allele conversions of ACV genes all occurred prior to the introduction of ACV. Sixteen percent of our isolates showed mutations within the prn gene. ACV and its booster doses (implemented for children in 2007 and adolescents in 2013) might have contributed to evolvement of a more uniform B. pertussis population, with recent circulating strains having ptxA1, ptxP3, and prn2 present, and an increasing number of prn mutations. These strains clearly deviate from ACV strains (ptxA1, ptxP1, prn1), and this could have implications for vaccine efficiency and, therefore, prevention and control of pertussis.

Pertactin-Deficient Bordetella pertussis with Unusual Mechanism of Pertactin Disruption, Spain, 1986-2018

Bordetella pertussis not expressing pertactin has increased in countries using acellular pertussis vaccines (ACV). The deficiency is mostly caused by pertactin gene disruption by IS481. To assess the effect of the transition from whole-cell vaccine to ACV on the emergence of B. pertussis not expressing pertactin in Spain, we studied 342 isolates collected during 1986–2018. We identified 93 pertactin-deficient isolates. All were detected after introduction of ACV and represented 38% of isolates collected during the ACV period; 58.1% belonged to a genetic cluster of isolates carrying the unusual prn::del(–292, 1340) mutation. Pertactin inactivation by IS481 insertion was identified in 23.7% of pertactin-deficient isolates, arising independently multiple times and in different phylogenetic branches. Our findings support the emergence and dissemination of a cluster of B. pertussis with an infrequent mechanism of pertactin disruption in Spain, probably resulting from introduction of ACV.

Macrolide susceptibility and molecular characteristics of Bordetella pertussis

Objective

To analyse macrolide resistance and molecular characteristics of Bordetella pertussis clinical isolates from western China, and to explore the relationship between macrolide-resistance and genotypes.

Methods

Susceptibilities of B. pertussis clinical isolates to erythromycin, azithromycin and clarithromycin were determined by epsilometer test (E-test). Isolated strains were sequenced to ascertain the presence of the 23S rRNA gene A2047G mutation. Strains were typed using multilocus antigen sequence typing, multilocus variable-number tandem-repeat analysis (MLVA) and pulsed-field gel electrophoresis (PFGE).

Results

Of 58 B. pertussis strains isolated in this study, 46 were macrolide-resistant and 12 were macrolide sensitive. All macrolide-resistant strains carried the A2047G mutation and were the prn1/ptxP1/ptxA1/fim3-1/fim2-1 genotype; the MLVA types were MT195 (19/58), MT55 (13/58) and MT104 (14/58), and the PFGE profiles were classified into BpSR23 (17/58) and BpFINR9 (29/58) types. None of the macrolide-sensitive strains carried the A2047G mutation; genotypes were (prn9 or prn2)/ptxP3/ptxA1/fim3-1/fim2-1, and all were MT27. PFGE profiles differed from the macrolide-resistant strains.

Conclusions

B. pertussis clinical isolates from western China were severely resistant to macrolides. Genotypes differed between macrolide-resistant and macrolide-sensitive strains, and there may be a correlation between acquisition of macrolide resistance and changes in specific molecular types.

Genotypes of Bordetella pertussis isolated from infants in Xi'an and Shanghai

OBJECTIVE

To compare the genotypes of Bordetella pertussis isolated from infants in Xi'an and Shanghai.

METHODS

Samples were collected by nasopharyngeal swab from infants aged <1 year hospitalized with suspected pertussis in Xi'an and Shanghai during 2018 and 2019. Bordetella pertussis was isolated, and multilocus antigen sequence typing (MAST) and multilocus variable-number tandem repeat analysis (MLVA) were used to analyse the genotypes.

RESULTS

A total of 1200 samples were collected from infants suspected of pertussis and 60 strains of Bordetella pertussis were isolated, including 34 strains in Xi'an and 26 strains in Shanghai. There were significant differences in the MAST types between Xi'an and Shanghai ( χ 2=18.642, P<0.01); the prn1/ ptxP1/ ptxA1/ fim3-1/ fim2-1 strains dominated in Xi'an (32/34, 94.12%), while the dominated MAST types in Shanghai were prn1/ ptxP1/ ptxA1/ fim3-1/ fim2-1 (13/26, 50.00%) and prn2/ ptxP3/ ptxA1/ fim3-1/ fim2-1 (11/26, 42.31%). The composition of MLVA type of pertussis strains was also significantly different between Xi'an and Shanghai ( χ 2=15.866, P<0.01); the MT195 (13/34, 38.24%), MT55 (10/34, 29.41%) and MT104 (9/34, 26.47%) strains dominated in Xi'an, while the MT27 (12/26, 46.15%) strain was most common in Shanghai.

CONCLUSION

There are differences in molecular types of Bordetella pertussis isolated from infants with suspected persussis in Xi'an and Shanghai, indicating that further monitoring of Bordetella pertussis is necessary for better understanding the pathogen evolution in China.

Evolutionary genomics of recent clinical Bordetella pertussis isolates from Iran: wide circulation of multiple ptxP3 lineages and report of the first ptxP3 filamentous hemagglutinin-negative B. pertussis

Here we investigated nationwide clinical Bordetella pertussis isolated during 2005-2017 from different provinces of Iran, a country with more than 50 years whole cell vaccine immunisation history. Our results revealed the ongoing increase in the population of ptxP3/fim3-2 B. pertussis isolates in different provinces which were differentiated into nine clades. The largest clade (clade 8) which was previously found to be prevalent in Tehran was also prevalent across the country and clade 5 with ptxP3/prn9 genotype has also increased in frequency (14% of all ptxP3 isolates) in recent years. Furthermore, we detected the first ptxP3 B. pertussis isolates that does not express filamentous hemagglutinin (FhaB) as one of the major antigens of the pathogen and a key component of the acellular pertussis vaccine.

Genomic Surveillance and Improved Molecular Typing of Bordetella pertussis Using wgMLST

Multilocus sequence typing (MLST) provides allele-based characterization of bacterial pathogens in a standardized framework. However, classical MLST schemes for Bordetella pertussis, the causative agent of whooping cough, seldom reveal diversity among the small number of gene targets and thereby fail to delineate population structure. To improve the discriminatory power of allele-based molecular typing of B. pertussis, we have developed a whole-genome MLST (wgMLST) scheme from 225 reference-quality genome assemblies. Iterative refinement and allele curation resulted in a scheme of 3,506 coding sequences and covering 81.4% of the B. pertussis genome. This wgMLST scheme was further evaluated with data from a convenience sample of 2,389 B. pertussis isolates sequenced on Illumina instruments, including isolates from known outbreaks and epidemics previously characterized by existing molecular assays, as well as replicates collected from individual patients. wgMLST demonstrated concordance with whole-genome single nucleotide polymorphism (SNP) profiles, accurately resolved outbreak and sporadic cases in a retrospective comparison, and clustered replicate isolates collected from individual patients during diagnostic confirmation. Additionally, a reanalysis of isolates from two statewide epidemics using wgMLST reconstructed the population structures of circulating strains with increased resolution, revealing new clusters of related cases. Comparison with an existing core genome (cgMLST) scheme highlights the stable gene content of this bacterium and forms the initial foundation for necessary standardization. These results demonstrate the utility of wgMLST for improving B. pertussis characterization and genomic surveillance during the current pertussis disease resurgence.

Rapid and simple SNP genotyping for Bordetella pertussis epidemic strain MT27 based on a multiplexed single-base extension assay

Multilocus variable-number tandem repeat analysis (MLVA) is widely used for genotyping of Bordetella pertussis, the causative bacteria for pertussis. However, MLVA genotyping is losing its discriminate power because prevalence of the epidemic MT27 strain (MLVA-27) is increasing worldwide. To address this, we developed a single nucleotide polymorphism (SNP) genotyping method for MT27 based on multiplexed single-base extension (SBE) assay. A total of 237 MT27 isolates collected in Japan during 1999–2018 were genotyped and classified into ten SNP genotypes (SG1 to SG10) with a Simpson’s diversity index (DI) of 0.79 (95% CI 0.76–0.82). Temporal trends showed a marked increase in the genotypic diversity in the 2010s: Simpson’s DI was zero in 1999–2004, 0.16 in 2005–2009, 0.83 in 2010–2014, and 0.76 in 2015–2018. This indicates that the SNP genotyping is applicable to the recently circulating MT27 strain. Additionally, almost all outbreak-associated MT27 isolates were classified into the same SNP genotypes for each outbreak. Multiplexed SBE assay allows for rapid and simple genotyping, indicating that the SNP genotyping can potentially be a useful tool for subtyping the B. pertussis MT27 strain in routine surveillance and outbreak investigations.

High Prevalence of Macrolide-Resistant Bordetella pertussis and ptxP1 Genotype, Mainland China, 2014-2016

According to the government of China, reported cases of pertussis have increased remarkably and are still increasing. To determine the genetic relatedness of Bordetella pertussis strains, we compared multilocus variable-number tandem-repeat analysis (MLVA) results for isolates from China with those from Western countries. Among 335 isolates from China, the most common virulence-associated genotype was ptxA1/ptxC1/ptxP1/prn1/fim2–1/fim3A/tcfA2, which was more frequent among isolates from northern than southern China. Isolates of this genotype were highly resistant to erythromycin. We identified 36 ptxP3 strains mainly harboring ptxA1 and prn2 (35/36); ptxP3 strains were sensitive to erythromycin and were less frequently from northern China. For all isolates, the sulfamethoxazole/trimethoprim MIC was low, indicating that this drug should be recommended for patients infected with erythromycin-resistant B. pertussis. MLVA of 150 clinical isolates identified 13 MLVA types, including 3 predominant types. Our results show that isolates circulating in China differ from those in Western countries.

Rare Detection of Bordetella pertussis Pertactin-Deficient Strains in Argentina

Pertussis resurgence had been attributed to waning vaccine immunity and Bordetella pertussis adaptation to escape vaccine-induced immunity. Circulating bacteria differ genotypically from strains used in production of pertussis vaccine. Pertactin-deficient strains are highly prevalent in countries that use acellular vaccine (aP), suggesting strong aP-imposed selection of circulating bacteria. To corroborate this hypothesis, systematic studies on pertactin prevalence of infection in countries using whole-cell vaccine are needed. We provide pertussis epidemiologic data and molecular characterization of B. pertussis isolates from Buenos Aires, Argentina, during 2000–2017. This area used primary vaccination with whole-cell vaccine. Since 2002, pertussis case incidences increased at regular 4-year outbreaks; most cases were in infants <1 year of age. Of the B. pertussis isolates analyzed, 90.6% (317/350) contained the ptxP3-ptxA1-prn2-fim3-2 allelic profile. Immunoblotting and sequencing techniques detected only the 2 pertactin-deficient isolates. The low prevalence of pertactin-deficient strains in Argentina suggests that loss of pertactin gene expression might be driven by aP vaccine.

Genomic epidemiology of Iranian Bordetella pertussis: 50 years after the implementation of whole cell vaccine

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.

Genome diversity and evolutionary characteristics of clinical isolates of Bordetella pertussis circulating in Iran

BACKGROUND AND OBJECTIVES

The re-emergence of pertussis still is being reported all over the world. Pathogen adaptation and antigenic divergence of circulating isolates from vaccine strains are the main reasons of infection resurgence. Waning immunity is also an important factor contributing to resurgence of pertussis.

MATERIALS AND METHODS

The genetic diversity and evolutionary characteristics of circulating Iranian isolates of Bordetella pertussis during February 2015 to October 2018 was investigated by pulsed-field gel electrophoresis (PFGE) and subsequently ptxA, ptxP and fim3 alleles were characterized. The next generation genome sequencing was then used to compare the genomics of ptxP1 and ptxP3 of selected isolates from PFGE dendrogram.

RESULTS

PFGE differentiated 62 clinical isolates and vaccine and reference strains into 19 PFGE profiles, indicating the higher level of heterogeneity in the population during 2015-2018. The predominant B. pertussis genotype harbored pertussis toxin promoter allele, ptxP3 and the expansion of ptxA1 isolates, were also observed in our population.

CONCLUSION

No changes in allelic profile of predominant clone in recent years was observed but antigenic divergence between recently circulating isolates and the vaccine strain has been progressed and significantly was higher than previous studies. The comparative genomic analysis of the ptxP3 and ptxP1 isolates indicate that changes in ptxP3 genome structure including 32 unique SNPs and three unique indels may have contributed to the expansion of the ptxP3 clone. We compared ptxP3 and ptxP1 isolates in pathogenicity-associated genes and found five of them were specific for the ptxP3 isolates. The polymorphisms in pathogenicity-associated genes suggest structural adaptations for these virulence factors.

Determining Factors for Pertussis Vaccination Policy: A Study in Five EU Countries

Pertussis vaccination policy varies across Europe, not only in the type of vaccine-whole cell (wP) vs. acellular (aP1/2/3/5)-but also in the schedule and recommendation for parents. This study aims to investigate the determining factors for the type of vaccine, immunization schedule and maternal immunization recommendation. From March to May 2019, experts in national health agencies and major academic or research institutions from Denmark, France, Poland, Sweden and the UK were invited to a semi-structured interview. Thematic analysis was performed on the transcripts using a codebook formulated by three coders. Inter-coder agreement was assessed. Fifteen expert interviews were conducted. The identified driving factors for pertussis vaccine policy were classified into three domains: scientific factors, sociological factors, and pragmatic factors. The determining factors for the type of vaccine were prescriber's preference, concern of adverse events following immunization (AEFI), effectiveness, and consideration of other vaccine components in combined vaccines. The determining factors for infant schedule were immunity response and the potential to improve coverage and timeliness. The determining factors for maternal immunization were infant mortality and public acceptability. To conclude, socio-political and pragmatic factors were, besides scientific factors, important in determining the pertussis vaccine type, schedule of childhood immunization and recommendations for parents.

Population dynamics and antigenic drift of Bordetella pertussis following whole cell vaccine replacement, Barcelona, Spain, 1986-2015

Among the factors associated with the resurgence of whooping cough, special emphasis has been given to pathogen adaptation after the introduction of the acellular vaccine (ACV). To assess the impact of the vaccine transition strategy from whole-cell vaccine (WCV) to ACV on population dynamics of Bordetella pertussis in Barcelona (Spain), we studied 339 isolates collected from 1986 to 2015 by PFGE and multi-locus variable-number tandem repeat analysis (MLVA). Additionally, allelic variants for the pertussis toxin and its promoter, pertactin, type 3 fimbriae and fimbrial serotyping were assessed to determine its antigenic drift. A shift was observed in the B. pertussis population as well as in its antigenic profile concurrently with the introduction of ACV in Barcelona. Four out of the five most prevalent PFGE profiles were replaced by new profiles following the ACV introduction. MLVA type 27 was the dominant genotype, and its frequency increased from 25% to 79.3% after WCV replacement. Antigen typing demonstrated the emergence of prn2, ptxP3, fim3-2 and a shift from the fimbriae 3 to the fimbriae 2 serotypes after the ACV introduction. Our findings support the presence of population and antigenic dynamic changes in B. pertussis likely driven by the introduction of ACV.

Pertussis: Identification, Prevention and Control

Pertussis is a vaccine-preventable disease. Despite the high vaccination coverage among children, pertussis is considered a re-emerging disease for which identification, prevention and control strategies need to be improved. To control pertussis it is important to maintain a high vaccination coverage to protect the age groups considered at high risk for the disease. Laboratory confirmation of Bordetella pertussis infection together with a differential diagnostic test for other Bordetellae are prerequisite for a correct and timely diagnosis of pertussis. Moreover, investigations of antimicrobial susceptibility and whole genome sequencing may permit to monitor the circulation of antimicrobials resistant and/or vaccine-escape strains. Finally, the preventive framework should no longer consider pertussis exclusively as a childhood infectious disease, since adults may play a role in transmission events.

Molecular Epidemiology of Bordetella pertussis

Although vaccination has been effective, Bordetella pertussis is increasingly causing epidemics, especially in industrialized countries using acellular vaccines (aPs). One factor behind the increased circulation is the molecular changes on the pathogen level. After pertussis vaccinations were introduced, changes in the fimbrial (Fim) serotype of the circulating strains was observed. When bacterial typing methods improved, further changes between the vaccine and circulating strains, especially among the common virulence genes including pertussis toxin (PT) and pertactin (PRN) were noticed. Moreover, development of genome based techniques including pulsed-field gel electrophoresis (PFGE), multiple-locus variable number tandem repeat analysis (MLVA) and whole-genome sequencing (WGS) have offered a better resolution to monitor B. pertussis strains. After the introduction of aP vaccines, B. pertussis strains that are deficient to vaccine antigens, especially PRN, have appeared widely. On the other hand, antimicrobial resistance to first line drugs (macrolides) against B. pertussis is still low in many countries and therefore no globally evaluated antimicrobial susceptibility test values have been recommended. In this review, we focus on the molecular changes in the bacteria, which have or may have affected the past and current epidemiology of pertussis.

Pertactin-deficient Bordetella pertussis isolates in Poland-a country with whole-cell pertussis primary vaccination

The introduction of pertussis vaccination in the 1950s resulted in a significant decrease in the incidence of disease. However, since the 1990s many highly vaccinated countries have observed the re-emergence of the disease. One of the causes of this phenomenon might be related to the adaptation of Bordetella pertussis to vaccination. The purpose of the presented study was an investigation of the emergence and spread of vaccine antigen-deficient B. pertussis isolates in Poland and genomic characterization of the currently circulating pathogen population using PFGE, MLVA and MAST. The results revealed that all tested isolates expressed Ptx, FHA and ACT antigens but 15.4% (4/26) of isolates from 2010 to 2016 were Prn-deficient. Moreover, one TcfA-deficient isolate was collected in 2015. The genotyping showed a genetic distinction between the isolates circulating in 2010-2016 and isolates from previous periods. The majority of currently circulating isolates belonged to PFGE group IV (96.2%), type MT27 (73.1%), and carried ptxA1-ptxC2-ptxP3-prn2-tcfA2-fim2-1-fim3-1 alleles (61.5%). The unique genetic structure of the B. pertussis population in Poland has changed since 2010 and became similar to that observed in countries with aP vaccination. This could be a result of increasing use of aP vaccines (60% of primary vaccination in 2013) over wP vaccines, which have been broadly used for primary vaccination in Poland for decades.

Pertussis epidemiology in Tunisian infants and children and characterization of Bordetella pertussis isolates: results of a 9-year surveillance study, 2007 to 2016

PURPOSE

Pertussis remains a public health concern in most countries. Our study aimed to prospectively explore the epidemiology of pertussis in the Tunis area of Tunisia between 2007 and 2016, and to characterize the virulence-associated genes of the collected Bordetella pertussis isolates.

METHODOLOGY

Infants and children hospitalized at the Children's Hospital of Tunis, Tunisia, between 2007 and 2016 for suspicion of pertussis were enrolled in the study. Culture and real-time PCR (qPCR) assays targeting IS481, IS1001, recA, H-IS1001 and ptxP were used to confirm the pertussis diagnosis. Phenotypic and genotypic characterization of recovered isolates was performed.Results/Key findings. A total of 1844 children were included in the study. Overall, 306 children (16.6 %) with Bordetella infection were confirmed by qPCR. Among them, 265 (86.6 %) were confirmed as having B. pertussis (IS481+, ptxP+, H-IS1001-), 18 (5.9 %) as having Bordetella parapertussis (IS481-, IS1001+) and 11 (3.6 %) as having Bordetella spp. (IS481+, ptxP-, H-IS1001-). No Bordetella holmesii (IS481+, IS1001-, H-IS1001+) was identified. The estimated pertussis incidence in the Tunis area was 134/100 000 in children aged less than 5 years. Two epidemic peaks were observed in 2009 and 2014. Ten B. pertussis isolates were cultured and characterized. Deficiency in pertactin expression was not observed, and genotyping of the isolates revealed a predominant allelic profile: ptxP3-ptxA1-prn2-fim2-1-fim3-2.

CONCLUSION

This study demonstrated that pertussis is still present as a cyclical disease in Tunisia, despite high primo-vaccination coverage with a pertussis whole-cell vaccine. The predominant genotype of Tunisian B. pertussis isolates is similar to isolates circulating in countries using the acellular vaccine.

Strain variation and antigenic divergence among Bordetella pertussis circulating strains isolated from patients in Iran

Despite global efforts and widespread vaccination to control whooping cough (pertussis) caused by B. pertussis, the re-emergence of pertussis still is being reported all over the world. Antigenic divergence in B. pertussis virulence factors is one of the reasons of pertussis resurgence, resulting in dissimilarity of local and vaccine strains. In this study, clonal spread and variation of B. pertussis virulence factor in isolated strains from Iranian patients have been analyzed. A total of 100 B. pertussis isolates were obtained from Pertussis Reference Laboratory of Pasteur Institute of Iran. Real-time PCR were performed to confirm the B. pertussis strains. The genomic patterns of B. pertussis strains were analyzed by pulsed-field gel electrophoresis (PFGE). Predominant alleles of local strains were ptxP3, ptxA1, prn2, fim 2-1, fim3-2, and cya2. PFGE results showed 25 patterns clustered into 18 PFGE groups. A few similarities between the circulating isolates, vaccine, and standard strains were obtained. Significantly, 48% of the isolates showed dominant pattern with different allelic profiles from vaccine strains. According to the genomic profiles, the clonal spread was observed among the circulating strains. Predominant virulence factor profile was also comparable with other countries. It may be suggested that strain variation between vaccine and local strains may have an effect on pertussis resurgence in Iran like other parts of the world.