Bordetella pertussis strains with increased toxin production associated with pertussis resurgence

A profile of the Simplexa™ Bordetella Direct assay for the detection and differentiation of Bordetella pertussis and Bordetella parapertussis in nasopharyngeal swabs

INTRODUCTION

Pertussis is a highly contagious respiratory infection caused by Bordetella pertussis and to minor extent B. parapertussis. Despite high vaccination coverage, epidemics persist worldwide. Laboratory testing with the capacity to support increasing demand and generate fast and accurate results is needed to promptly provide treatment to mitigate symptoms, prevent transmission, and thus impact infection control and disease surveillance.

AREAS COVERED

This review will describe the features of the Simplexa™ Bordetella Direct Assay and compare this technology with other existing assays. Unmet needs and future directions will be discussed.

EXPERT COMMENTARY

Resurgence of pertussis highlights the importance of reliable and accurate diagnosis. The Simplexa™ Bordetella Direct Assay provides an easy workflow, reduced hand-on time, less risk of contamination, and rapid turnaround time. The use of efficient molecular assays in routine clinical laboratory is valuable for increasing demand, improvement of infection control, and surveillance.

Effect of FHA and Prn on Bordetella pertussis colonization of mice is dependent on vaccine type and anatomical site

Bordetella pertussis vaccine escape mutants that lack expression of the pertussis antigen pertactin (Prn) have emerged in vaccinated populations in the last 10–20 years. Additionally, clinical isolates lacking another acellular pertussis (aP) vaccine component, filamentous hemagglutinin (FHA), have been found sporadically. Here, we show that both whole-cell pertussis (wP) and aP vaccines induced protection in the lungs of mice, but that the wP vaccine was more effective in nasal clearance. Importantly, bacterial populations isolated from the lungs shifted to an FHA-negative phenotype due to frameshift mutations in the fhaB gene. Loss of FHA expression was strongly selected for in Prn-deficient strains in the lungs following aP but not wP vaccination. The combined loss of Prn and FHA led to complete abrogation of bacterial surface binding by aP-induced serum antibodies. This study demonstrates vaccine- and anatomical site-dependent adaptation of B. pertussis and has major implications for the design of improved pertussis vaccines.

Acellular Pertussis Vaccine Components: Today and Tomorrow

Pertussis is a highly communicable acute respiratory infection caused by Bordetella pertussis. Immunity is not lifelong after natural infection or vaccination. Pertussis outbreaks occur cyclically worldwide and effective vaccination strategies are needed to control disease. Whole-cell pertussis (wP) vaccines became available in the 1940s but have been replaced in many countries with acellular pertussis (aP) vaccines. This review summarizes disease epidemiology before and after the introduction of wP and aP vaccines, discusses the rationale and clinical implications for antigen inclusion in aP vaccines, and provides an overview of novel vaccine strategies aimed at better combating pertussis in the future.

Allele frequencies of Bordetella pertussis virulence-associated genes identified from pediatric patients with severe respiratory infections

Bordetella pertussis (B. pertussis) infection occasionally causes severe respiratory infections in children. Potential association between virulence-associated gene alleles and severe clinical outcomes has been suggested; however, frequencies of these alleles in pediatric patients with severe pertussis have not been clarified. We retrospectively tested stored respiratory samples collected from B. pertussis-positive patients by polymerase chain reaction targeting for major virulence-associated genes; fimbrae (fim) serotype 3 (fim3), pertactin (prn), pertussis toxin A (ptxA), and pertussis toxin promotor (ptxP). Based on the identified sequences, multilocus sequence typing (MLST) was conducted. Association of gene allele frequency and clinical outcomes such as management in pediatric intensive care unit, intubation, and mortality was analyzed. Out of 25 patients with available samples, the most prevalent allele for each virulence-associated gene was fim3A (17/21, 83%), ptxA1 (20/23, 87%), prn2 (13/16, 81%), and ptxP3 (14/17, 82%). In the study, total of 3 MLST types were identified; MLST-1 from 3 patients (19%), MLST-2 from 10 patients (63%), and MLST-4 from 3 patients (19%). Detection rate of the major MLST type; MLST-2 was significantly higher for patients who required intubation compared to those who did not (6/6, 100% vs 4/10, 40%; p = 0.034). In conclusion, MLST-2 was the most common MLST type in B. pertussis isolated from Japanese children with severe pertussis. Further studies investigating its causal association with disease severity is warranted.

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.

Bordetella pertussis induces IFN-γ production by NK cells resulting in chemo-attraction by respiratory epithelial cells

BACKGROUND

Whooping cough is caused by infection of the airways with Bordetella pertussis (Bp). As IFN-γ is essential for protective immunity against Bp we investigated how IFN-γ is induced by Bp or the virulence antigens FHA, Prn or PT, and how IFN-γ contributes to local immune responses in humans.

METHODS

PBMCs from healthy donors and/or respiratory epithelial cells were stimulated with soluble antigens or inactivated intact Bp and the presence or absence of blocking antibodies or chemokines. Supernatants and cells were analyzed for IFN-γ and chemokine production and lymphocyte migration tested using epithelial supernatants.

RESULTS

The soluble antigens failed to induce IFN-γ production, whereas inactivated Bp induced IFN-γ production. NK cells were the main source of IFN-γ production, which was enhanced by IL-15. Epithelial-PBMC co-cultures showed robust IFN-γ-dependent CXCL9 and CXCL10 production by the epithelial cells following stimulation with IFN-γ and Bp. The epithelial-derived chemokines resulted in CXCR3-dependent recruitment of NK and T cells.

CONCLUSIONS

Inactivated Bp, but not antigens, induced potent IFN-γ production by NK cells, resulting in chemo-attraction of lymphocytes towards the respiratory epithelium. These data provide insight into the requirements for IFN-γ production and how IFN-γ enhances local immune responses to prevent Bp-mediated disease.

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.

Impact of maternal dTpa vaccination on the incidence of pertussis in young infants

Introduction

Pertussis is an important public health problem worldwide, especially in infants. An increase in the incidence in many countries occurred after 2010, including Brazil. In 2013, dTpa vaccine was introduced in the Brazil national immunization schedule of pregnant women. The objective of this study was to evaluate the national trends in the incidence of pertussis in Brazil in children under 1 year old, and the impact of the introduction of dTpa vaccine during pregnancy.

Methods

The incidence of hospitalizations and non-hospitalized confirmed cases of pertussis in neonates (< 1 month age) and young infants (1 month—< 1 year age) were analyzed, comparing the incidence in pre maternal vaccination (2011–2013) with the post-vaccination (2015–2017). We used non-respiratory hospitalizations as comparison, during the same period. A database of the Brazilian Ministry of Health (DATASUS) was used to analyze cases from 2007 to 2017 and the subsets of 2011–2013 and 2015–2017, after Pertussis resurgence. The vaccination data was accessed through the link of the Information System of the National Immunization Program (pni.datasus.gov.br).

Results

Between 2007 and 2017, 17,818 children under one year of age were hospitalized due to pertussis in Brazil. In the pre maternal vaccination period 2011–2013, the mean annual incidence of non-hospitalized confirmed cases of pertussis in children under 1 month was 722.2 / 100,000 and in the period of 2015–2017 the average was 377.3 / 100,000, representing a decrease of 47.7% [IRR 0.52 (0.46–0.59)]. At those periods of time, the average incidence per year for children of one month—< 1 year aged was 64.9 / 100,000 (2011–2013) and 29.3 / 100,000 (2015–2017) [IRR 0.45 (CI 0.29–0.69)].

Conclusion

Vaccination of pregnant woman coincides with the reduction in the number of cases of pertussis in children under 1 month of age from 2015. Immunization of pregnant woman seems to have an important impact on the prevention of the disease in young infants who have not yet received their own pertussis vaccine.

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.

Vaccine-driven virulence evolution: consequences of unbalanced reductions in mortality and transmission and implications for pertussis vaccines

Many vaccines have heterogeneous effects across individuals. Additionally, some vaccines do not prevent infection, but reduce disease-associated mortality and transmission. Both of these factors will alter selection pressures on pathogens and thus shape the evolution of pathogen virulence. We use a mathematical modelling framework to show that (i) the balance of how vaccines reduce transmission versus mortality and (ii) individual variability in protection conferred both shape the evolution of pathogen virulence. Epidemiological (burden of disease) and evolutionary (pathogen virulence) outcomes are both worse when vaccines confer smaller reductions in transmission than in mortality. Furthermore, outcomes are modulated by variability in vaccine effects, with increased variability limiting the extent of virulence evolution but in some cases preventing eradication. These findings are pertinent to current concerns about the global resurgence of pertussis and the efficacy of pertussis vaccines, as the two classes of these vaccines may reduce disease symptoms without preventing infection and differ in their ability to reduce transmission. Furthermore, these findings point to the importance of generating precise predictions for virulence evolution in Bordetella pertussis (and other similar pathogens) by incorporating empirical characterizations of vaccine effects into models capturing the epidemiological details of this system.

Trends in Hospital Admissions for Pertussis Infection: A Nationwide Retrospective Observational Study in Italy, 2002-2016

Background: Pertussis is a highly contagious infectious disease which continues to be an important public-health issue despite the high immunization coverage rates achieved. However, evidence of increased circulation of pertussis among adolescents and adults due to waning immunity and atypical clinical manifestations seem to be the main reasons for its resurgence. The aim of this study was the analysis of the epidemiological trend for pertussis-related hospitalizations in Italy, in relation with vaccination coverage and information from laboratory confirmed cases of pertussis. Methods: A retrospective observational study investigating hospitalizations for pertussis from 2002 to 2016 in Italy was conducted. Frequencies and rates of hospitalization were analyzed and hospitalization data were compared with a series of already published laboratory confirmed data. Results: This study highlighted a rising trend for pertussis hospitalizations in Italy since 2008. Infants aged <1 year showed the highest frequencies (63.39%) and average rates (74.60 × 100000 infants) of hospitalization despite an extremely high vaccination coverage (95.89%). An increasing trend of hospitalization frequency emerged for the age group with levels of IgG antibodies to pertussis toxin compatible with pertussis infection within the last year (20–29 years old age group). Conclusions: The rising trend for pertussis hospitalizations and the greater involvement of infants aged <1 year require an integrated approach, including the implementation of booster doses administration in adolescence and adulthood, the vaccination of pregnant women and the cocoon strategy.

Surfaceome analysis of Australian epidemic Bordetella pertussis reveals potential vaccine antigens

Since acellular vaccines (ACV) were introduced in Australia, epidemic Bordetella pertussis strains changed from single nucleotide polymorphism (SNP) cluster II to SNP cluster I. Our previous proteomic analysis identified potential proteomic adaptations in the whole cell and secretome of SNP cluster I. Additionally, current ACVs were shown to be less efficacious against cluster I in mice models and there is a pressing need to discover new antigens to improve the ACV. One important source of novel antigens is the surfaceome. Therefore, in this study we established surface shaving in B. pertussis to compare the surfaceome of SNP cluster I (L1423) and II (L1191), and identify novel surface antigens for vaccine development. Surface shaving using 1 μg of trypsin for 5 min identified 126 proteins with the most abundant being virulence-associated and known outer membrane proteins. Cell viability counts showed minimal lysis from shaving. The proportion of immunogenic proteins was higher in the surfaceome than in the whole cell and secretome. Key differences in the surfaceome were identified between SNP cluster I and II, consistent with those identified in the whole cell proteome and secretome. These differences include unique transport proteins and decreased immunogenic proteins in L1423, and provides further evidence of proteomic adaptation in SNP cluster I. Finally, a comparison of proteins in each sub-proteome identified 22 common proteins. These included 11 virulence proteins (Prn, PtxA, FhaB, CyaA, TcfA, SphB1, Vag8, BrkA, BopD, Bsp22 and BipA) and 11 housekeeping proteins (TuF, CtpA, TsF, OmpH, GltA, SucC, SucD, FusA, GroEL, BP3330 and BP3561) which were immunogenic, essential and consistently expressed thus demonstrating their potential as future targets. This study established surface shaving in B. pertussis, confirmed key expression differences and identified unknown surface proteins which may be potential vaccine antigens.

Adaptation of Bordetella pertussis to the Respiratory Tract

There is a lack of insight into the basic mechanisms by which Bordetella pertussis adapts to the local host environment during infection. We analyzed B. pertussis gene expression in the upper and lower airways of mice and compared this to SO4-induced in vitro Bvg-regulated gene transcription. Approximately 30% of all genes were differentially expressed between in vitro and in vivo conditions. This included several novel potential vaccine antigens that were exclusively expressed in vivo. Significant differences in expression profile and metabolic pathways were identified between the upper versus the lower airways, suggesting distinct antigenic profiles. We found high-level expression of several Bvg-repressed genes during infection, and mouse vaccination experiments using purified protein fractions from both Bvg- and Bvg+ cultures demonstrated protection against intranasal B. pertussis challenge. This study provides novel insights into the in vivo adaptation of B. pertussis and may facilitate the improvement of pertussis vaccines.

Activation of Human NK Cells by Bordetella pertussis Requires Inflammasome Activation in Macrophages

Pertussis is a highly contagious respiratory infection caused by the bacterium Bordetella pertussis. Humans are the only known natural reservoir of B. pertussis. In mice, macrophages and NK cells have a key role in confining B. pertussis to the respiratory tract. However, the mechanisms underlying this process, particularly during human infections, remain unclear. Here we characterized the activation of human macrophages and NK cells in response to B. pertussis and unraveled the role of inflammasomes in this process. NLRP3 inflammasome activation by B. pertussis in human macrophage-like THP-1 cells and primary monocyte-derived macrophages (mo-MΦ) was shown by the visualization of ASC-speck formation, pyroptosis, and the secretion of caspase-mediated IL-1β and IL-18. In contrast to macrophages, stimulation of human CD56⁺CD3⁻ NK cells by B. pertussis alone did not result in activation of these cells. However, co-culture of B. pertussis-stimulated mo-MΦ and autologous NK cells resulted in high amounts of IFNγ secretion and an increased frequency of IL-2Rα⁺ and HLA-DR⁺ NK cells, indicating NK cell activation. This activation was significantly reduced upon inhibition of inflammasome activity or blocking of IL-18 in the mo-MΦ/NK cell co-culture. Furthermore, we observed increased secretion of proinflammatory cytokines in the B. pertussis-stimulated mo-MΦ/NK co-culture compared to the mo-MΦ single culture. Our results demonstrate that B. pertussis induces inflammasome activation in human macrophages and that the IL-18 produced by these cells is required for the activation of human NK cells, which in turn enhances the pro-inflammatory response to this pathogen. Our data provides a better understanding of the underlying mechanisms involved in the induction of innate immune responses against B. pertussis. These findings contribute to the knowledge required for the development of improved intervention strategies to control this highly contagious disease.

Genomic epidemiology of erythromycin-resistant Bordetella pertussis in China

Macrolides such as erythromycin are the empirical treatment of Bordetella pertussis infections. China has experienced an increase in erythromycin-resistant B. pertussis isolates since they were first reported in 2013. Here, we undertook a genomic study on Chinese B. pertussis isolates from 2012 to 2015 to elucidate the origins and phylogenetic relationships of erythromycin-resistant B. pertussis isolates in China. A total of 167 Chinese B. pertussis isolates were used for antibiotic sensitivity testing and multiple locus variable-number tandem repeat (VNTR) analysis (MLVA). All except four isolates were erythromycin-resistant and of the four erythromycin-sensitive isolates, three were non-ptxP1. MLVA types (MT), MT55, MT104 and MT195 were the predominant types. Fifty of those isolates were used for whole genome sequencing and phylogenetic analysis. Genome sequencing and phylogenetic analysis revealed three independent erythromycin-resistant lineages and all resistant isolates carried a mutation in the 23S rRNA gene. A novel fhaB3 allele was found uniquely in Chinese ptxP1 isolates and these Chinese ptxP1-ptxA1-fhaB3 had a 5-fold higher mutation rate than the global ptxP1-ptxA1 B. pertussis population. Our results suggest that the evolution of Chinese B. pertussis is likely to be driven by selection pressure from both vaccination and antibiotics. The emergence of the new non-vaccine fhaB3 allele in Chinese B. pertussis population may be a result of selection from vaccination, whereas the expansion of ptxP1-fhaB3 lineages was most likely to be the result of selection pressure from antibiotics. Further monitoring of B. pertussis in China is required to better understand the evolution of the pathogen.

Pertussis Prevention: Reasons for Resurgence, and Differences in the Current Acellular Pertussis Vaccines

Pertussis is an acute respiratory disease caused by Bordetella pertussis. Due to its frequency and severity, prevention of pertussis has been considered an important public health issue for many years. The development of the whole-cell pertussis vaccine (wPV) and its introduction into the pediatric immunization schedule was associated with a marked reduction in pertussis cases in the vaccinated cohort. However, due to the frequency of local and systemic adverse events after immunization with wPV, work on a less reactive vaccine was undertaken based on isolated B. pertussis components that induced protective immune responses with fewer local and systemic reactions. These component vaccines were termed acellular vaccines and contained one or more pertussis antigens, including pertussis toxin (PT), filamentous haemagglutinin (FHA), pertactin (PRN), and fimbrial proteins 2 (FIM2) and 3 (FIM3). Preparations containing up to five components were developed, and several efficacy trials clearly demonstrated that the aPVs were able to confer comparable short-term protection than the most effective wPVs with fewer local and systemic reactions. There has been a resurgence of pertussis observed in recent years. This paper reports the results of a Consensus Conference organized by the World Association for Infectious Disease and Immunological Disorders (WAidid) on June 22, 2018, in Perugia, Italy, with the goal of evaluating the most important reasons for the pertussis resurgence and the role of different aPVs in this resurgence.

Role of Evolutionary Selection Acting on Vaccine Antigens in the Re-Emergence of Bordetella Pertussis

Pertussis (“whooping cough”) is a re-emerging disease with increasing incidence among fully vaccinated individuals. We explored the genetic diversity of five Bordetella pertussis proteins used to generate the subunit vaccine across ancestral and newly emergent strains using immunoinformatics and evolutionary selection measurements. The five subunits of pertussis toxin (Ptx1–Ptx5) were highly conserved with regard to sequence, predicted structure, predicted antigenicity, and were under purifying selection. In contrast, the adhesin proteins pertactin (Prn) and filamentous hemagglutinin (FHA) were under statistically significant (p < 0.01) diversifying selection. Most heavily diversified sites of each protein fell within antigenic epitopes, and the functional adhesin motifs were conserved. Protein secondary structure was conserved despite sequence diversity for FHA but was changeable in Prn. These findings suggest that subunit vaccine-derived immunity does not impact Ptx1–Ptx5 but may apply evolutionary pressure to Prn and FHA to undergo diversifying selection. These findings offer further insight into the emergence of vaccine-resistant strains of B. pertussis.

Bordetella pertussis Infection in Infants and Young Children in Shanghai, China, 2016-2017: Clinical Features, Genotype Variations of Antigenic Genes and Macrolides Resistance

BACKGROUND

The global resurgence of pertussis in countries with high vaccination coverage has been a concern of public health.

METHODS

Nasopharyngeal swabs were collected for Bordetella pertussis culture from children with suspected pertussis. Clinical and vaccination information were reviewed through electronic medical chart and immunization record. Antibiotics susceptibility was evaluated using E-test for erythromycin, azithromycin, clarithromycin and sulfamethoxazole/trimethoprim. The MLST genotypes and 7 antigenic genes (ptxP, ptxA, ptxC, Prn, fim3, fim2 and tcfA) of Bordetella pertussis were identified by polymerase chain reaction amplification and sequencing.

RESULTS

During January 2016 to September 2017, a total of 141 children 1-48 months of age were culture-confirmed with pertussis, of whom 98 (69.5%) were younger than 6 months, 25 (17.7%) had completed at least 3 doses of DTaP and 75 (53.2%) had a clear exposure to household members with persistent cough. Fully vaccinated cases manifested milder disease than unvaccinated and not-fully vaccinated cases. All strains were MLST2. High-virulent strains characteristic of ptxP3/prn2/ptxC2 constituted 41.1% (58/141) and were all susceptible to macrolides while low-virulent strains characteristic of ptxP1/prn1/ptxC1 constituted 58.9% (83/141) and 97.6% (81/83), respectively, were highly resistant to macrolides.

CONCLUSIONS

Pertussis is resurging among infants and young children in Shanghai, and household transmission is the main exposure pathway. The high-virulent strains harboring ptxP3/prn2/ptxC2 and the macrolide-resistant Bordetella pertussis strains are quite prevalent. These issues impose a public health concern in Shanghai. Our findings are important to modify the DTaP vaccination strategy and the management guideline of pertussis in China.

Recombinant outer membrane protein Q and putative lipoprotein from Bordetella pertussis inducing strong humoral response were not protective alone in the murine lung colonization model

Despite high vaccination coverage after introduction of whole cell (wP) and acellular pertussis (aP) vaccines, pertussis resurgence has been reported in many countries. aP vaccines are commonly preferred due to side effects of wP vaccines and formulated with aluminum hydroxide (Alum), which is not an effective adjuvant to eliminate Bordetella pertussis. Low efficiency of current aP vaccines is thought to be the main reason for the resurgence for which newer generation aP vaccines are needed. In the present study, immunogenicity and protective efficacy of outer membrane protein Q (OmpQ) and a putative lipoprotein (Lpp) from B. pertussis were investigated in mice by using two diefrent adjuvants, monophosphoryl lipid A (MPLA) or Alum. OmpQ and putative Lpp were cloned, expressed, and purified from Escherichia coli. The proteins were formulated to immunize mice. Both recombinant OmpQ and putative Lpp induced a significant increase in immunoglobulin G1 (IgG1) and immunoglobulin G2a (IgG2a) responses compared to the control group. Moreover, MPLA-adjuvanted formulations resulted in higher IgG2a levels than Alum-adjuvanted ones. However, there were no significant differences between test and control groups regarding interferon-gamma (IFN-γ) levels, and the mice lung colonization experiments indicated that neither rOmpQ nor rLpp could confer protection alone against B. pertussis challenge.

Immunogenicity and protective potential of Bordetella pertussis biofilm and its associated antigens in a murine model

The resurgence of whooping cough reflects novel genetic variants of Bordetella pertussis and inadequate protection conferred by current acellular vaccines (aP). Biofilm is a source of novel vaccine candidates, including membrane protein assembly factor (BamB) and lipopolysaccharide assembly protein (LptD). Responses of BALB/c mice to candidate vaccines included IFN-γ and IL-17a production by spleen and lymph node cells, and serum IgG1 and IgG2a reactive with whole bacteria or aP. Protection was determined using bacterial cultured from lungs of vaccinated mice challenged with virulent B. pertussis. Mice vaccinated with biofilm produced efficient IFN-γ responses and more IL-17a and IgG2a than mice vaccinated with planktonic cells, aP or adjuvant alone. Vaccination with aP produced abundant IgG1 with little IgG2a. Mice vaccinated with aP plus BamB and LptD retained lower bacterial loads than mice vaccinated with aP alone. Whooping cough vaccines formulated with biofilm antigens, including BamB and LptD, may have clinical value.

How Genomics Is Changing What We Know About the Evolution and Genome of Bordetella pertussis

The evolution of Bordetella pertussis from a common ancestor similar to Bordetella bronchiseptica has occurred through large-scale gene loss, inactivation and rearrangements, largely driven by the spread of insertion sequence element repeats throughout the genome. B. pertussis is widely considered to be monomorphic, and recent evolution of the B. pertussis genome appears to, at least in part, be driven by vaccine-based selection. Given the recent global resurgence of whooping cough despite the wide-spread use of vaccination, a more thorough understanding of B. pertussis genomics could be highly informative. In this chapter we discuss the evolution of B. pertussis, including how vaccination is changing the circulating B. pertussis population at the gene-level, and how new sequencing technologies are revealing previously unknown levels of inter- and intra-strain variation at the genome-level.

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.

Why the evolution of vaccine resistance is less of a concern than the evolution of drug resistance

Vaccines and antimicrobial drugs both impose strong selection for resistance. Yet only drug resistance is a major challenge for 21st century medicine. Why is drug resistance ubiquitous and not vaccine resistance? Part of the answer is that vaccine resistance is far less likely to evolve than drug resistance. But what happens when vaccine resistance does evolve? We review six putative cases. We find that in contrast to drug resistance, vaccine resistance is harder to detect and harder to confirm and that the mechanistic basis is less well understood. Nevertheless, in the cases we examined, the pronounced health benefits associated with vaccination have largely been sustained. Thus, we contend that vaccine resistance is less of a concern than drug resistance because it is less likely to evolve and when it does, it is less harmful to human and animal health and well-being. Studies of pathogen strains that evolve the capacity to replicate and transmit from vaccinated hosts will enhance our ability to develop next-generation vaccines that minimize the risk of harmful pathogen evolution.

Peptidoglycan Recognition Protein 4 Suppresses Early Inflammatory Responses to Bordetella pertussis and Contributes to Sphingosine-1-Phosphate Receptor Agonist-Mediated Disease Attenuation

Incidence of whooping cough (pertussis), a bacterial infection of the respiratory tract caused by the bacterium Bordetella pertussis, has reached levels not seen since the 1950s. Antibiotics fail to improve the course of disease unless administered early in infection. Therefore, there is an urgent need for the development of antipertussis therapeutics. Sphingosine-1-phosphate receptor (S1PR) agonists have been shown to reduce pulmonary inflammation during Bordetella pertussis infection in mouse models. However, the mechanisms by which S1PR agonists attenuate pertussis disease are unknown. We report the results of a transcriptome sequencing study examining pulmonary transcriptional responses in B. pertussis-infected mice treated with S1PR agonist AAL-R or vehicle control. This study identified peptidoglycan recognition protein 4 (PGLYRP4) as one of the most highly upregulated genes in the lungs of infected mice following S1PR agonism. PGLYRP4, a secreted, innate mediator of host defenses, was found to limit early inflammatory pathology in knockout mouse studies. Further, S1PR agonist AAL-R failed to attenuate pertussis disease in PGLYRP4 knockout (KO) mice. B. pertussis virulence factor tracheal cytotoxin (TCT), a secreted peptidoglycan breakdown product, induces host tissue damage. TCT-oversecreting strains were found to drive an early inflammatory response similar to that observed in PGLYRP4 KO mice. Further, TCT-oversecreting strains induced significantly greater pathology in PGLYRP4-deficient animals than their wild-type counterparts. Together, these data indicate that S1PR agonist-mediated protection against pertussis disease is PGLYRP4 dependent. Our data suggest PGLYRP4 functions, in part, by preventing TCT-induced airway damage.

Comparison of the Whole Cell Proteome and Secretome of Epidemic Bordetella pertussis Strains From the 2008-2012 Australian Epidemic Under Sulfate-Modulating Conditions

Sulfate is an important modulator for virulence factor expression in Bordetella pertussis, the causative organism for whooping cough. During infection, sulfate is released when respiratory epithelial cells are damaged which can affect gene expression. The current predominant strains in Australia are found in single nucleotide polymorphism (SNP) cluster I (ptxP3/prn2). It has been reported that ptxP3 strains have higher mRNA expression of virulence genes than ptxP1 strains under intermediate sulfate-modulating conditions (5 mM MgSO₄). Our previous proteomic study compared L1423 (cluster I, ptxP3) and L1191 (cluster II, ptxP1) in Thalen-IJssel (THIJS) media without sulfate modulation and identified an upregulation of transport proteins and a downregulation of immunogenic proteins. To determine whether proteomic differences exist between cluster I and cluster II strains in intermediate modulating conditions, this study compared the whole cell proteome and secretome between L1423 and L1191 grown in THIJS media with 5 mM MgSO₄ using iTRAQ and high-resolution multiple reaction monitoring (MRM-hr). Two proteins (BP0200 and BP1175) in the whole cell were upregulated in L1423 [fold change (FC) >1.2, false discovery rate (FDR) <0.05]. In the secretome, four proteins from the type III secretion system (T3SS) effectors were downregulated (FC < 0.8, FDR < 0.05) while six proteins, including two adhesins, pertactin (Prn) and tracheal colonization factor A (TcfA), were upregulated which were consistent with our previous proteomic study. The upregulation of Prn and TcfA in SNP cluster I may result in improved adhesion while the downregulation of the T3SS and other immunogenic proteins may reduce immune recognition, which may contribute to the increased fitness of cluster I B. pertussis strains.

Emerging of ptxP3 lineage in Bordetella pertussis strains circulating in a population in northeastern Mexico

We determined the molecular epidemiology of Bordetella pertussis isolates to evaluate its potential impact on pertussis reemergence in a population of Mexico. Symptomatic and asymptomatic cases were included. Pertussis infection was confirmed by culture and real-time polymerase chain reaction (PCR). Selected B. pertussis isolates were further analysed; i.e. clonality was analysed by pulsed-field gel electrophoresis (PFGE) and ptxP-ptxA, prn, fim2 and fim3 typing was performed by PCR and sequencing. Out of 11 864 analysed samples, 687 (5.8%) were positive for pertussis, with 244 (36%) confirmed by both culture and PCR whereas 115 (17%) were positive only by culture and 328 (48%) were positive only by PCR. One predominant clone (clone A, n = 62/113; 55%) and three major subtypes (A1, A2 and A3) were identified by PFGE. All 113 selected isolates had the allelic combination ptxP3-ptxA1. The predominant clone A and the three major subtypes (A1, A2 and A3) corresponded to the emerging genotypes ptxP3-ptxA1-prn2-fim2-1-fim3-2 and ptxP3-ptxA1-prn2-fim2-1-fim3-1. In conclusion, the presence of an endemic clone and three predominant subtypes belonging to the genotypes ptxP3-ptxA1-prn2-fim2-1-fim3-2 and ptxP3-ptxA1-prn2-fim2-1-fim3-1 were detected. This finding supports the global spread/expansion reported for these outbreaks associated genotypes.

Prevention of pertussis: An unresolved problem

Pertussis is a highly contagious respiratory disease caused by Bordetella pertussis. However, after the introduction of the whole-cell pertussis vaccine (wP), the annual incidence rates of the disease progressively declined. Despite this result, the inclusion of wP in the national immunization schedule of infants and young children was debated regarding its safety. Several efforts to produce vaccines based on B. pertussis components capable of evoking protective immunity with no or limited adverse events were made. Of these others, five pertussis antigens were considered possible components of acellular vaccines (aPs): pertussis toxin (PT), filamentous haemagglutinin (FHA), pertactin (PRN) and fimbria proteins 2 and 3. However, the introduction of aPs was followed by a slight but progressive increase in the incidence of pertussis. This paper discusses the potential reasons for reduced aPs efficacy. Moreover, it attempts to evaluate the real effectiveness of aPs and the potential differences between available preparations. Data analysis showed that several boosters are needed to maintain protection against pertussis and additional studies are needed to confirm the antigens that should be included in aPs to improve the prevention of pertussis.

Protective effects of in vivo-expressed autotransporters against Bordetella pertussis infection

Bordetella pertussis causes whooping cough, a severe and prolonged respiratory disease that results inhas high morbidity and mortality rates, particularly in developing countries. The number incidence of whooping cough cases is increasing in many countries despite high vaccine coverage. Causes for the re-emergence of the disease include the limited duration of protection conferred by the acellular pertussis vaccines (aP)s and pathogenic adaptations that involve antigenic divergence from vaccine strains. Therefore, current vaccines therefore need to be improved. In the present study, we focused on five autotransporters: namely SphB1, BatB, SphB2, Phg, and Vag8, which were previously found to be expressed by B. bronchiseptica during the course of infection in rats and examined their protective efficiencies as vaccine antigens. The passenger domains of these proteins were produced in recombinant forms and used as antigens. An intranasal murine challenge assay showed that immunization with a mixture of SphB1 and Vag8 (SV) significantly reduced bacterial load in the lower respiratory tract and a combination of aP and SV acts synergistically in effects of conferring protection against B. pertussis infection, implying that these antigens have potential as components to for improvinge th the currently available acellular pertussis vaccine.

The Adjuvant Bordetella Colonization Factor A Attenuates Alum-Induced Th2 Responses and Enhances Bordetella pertussis Clearance from Mouse Lungs

The reemergence of pertussis or whooping cough in several countries highlights the need for better vaccines. Acellular pertussis vaccines (aPV) contain alum as the adjuvant and elicit Th2-biased immune responses that are less effective in protecting against infection than the reactogenic whole-cell pertussis vaccines (wPV), which elicit primarily a Th1/Th17 response. An important goal for the field is to devise aPV that will induce immune responses similar to those of wPV. We show that Bordetella colonization factor A (BcfA), an outer membrane protein from Bordetella bronchiseptica, has strong adjuvant function and elicits cellular and humoral immune responses to heterologous and Bordetella pertussis antigens. Addition of BcfA to a commercial aPV resulted in greater reduction of B. pertussis numbers from the lungs than that elicited by aPV alone. The more-efficient pathogen clearance was accompanied by increased interleukin-17 (IL-17) and reduced IL-5 and an increased ratio of IgG2/IgG1 antibodies. Thus, our results suggest that BcfA improves aPV-induced responses by modifying the alum-induced Th2-biased aPV response toward Th1/Th17. A redesigned aPV containing BcfA may allow better control of pertussis reemergence by reshaping immune responses to resemble those elicited by wPV immunization.

Bordetella pertussis population dynamics and phylogeny in Japan after adoption of acellular pertussis vaccines

Bordetella pertussis, the causative agent of whooping cough, has experienced a resurgence in the past 15 years, despite the existence of both whole-cell and acellular vaccines. Here, we performed whole genome sequencing analysis of 149 clinical strains, provided by the National Institute of Infectious Diseases (NIID), Japan, isolated in 1982–2014, after Japan became the first country to adopt acellular vaccines against B. pertussis. Additionally, we sequenced 39 strains provided by the Konan Kosei Hospital in Aichi prefecture, Japan, isolated in 2008–2013. The genome sequences afforded insight into B. pertussis genome variability and population dynamics in Japan, and revealed that the B. pertussis population in Japan was characterized by two major clades that divided more than 40 years ago. The pertactin gene was disrupted in about 20 % of the 149 NIID isolates, by either a deletion within the signal sequence (ΔSS) or the insertion of IS element IS481 (prn :: IS481). Phylogeny suggests that the parent clones for these isolates originated in Japan. Divergence dating traced the first generation of the pertactin-deficient mutants in Japan to around 1990, and indicated that strains containing the alternative pertactin allele prn2 may have appeared in Japan around 1974. Molecular clock data suggested that observed fluctuations in B. pertussis population size may have coincided with changes in vaccine usage in the country. The continuing failure to eradicate the disease warrants an exploration of novel vaccine compositions.

Resurgence of Pertussis and Emergence of the Ptxp3 Toxin Promoter Allele in South Italy

BACKGROUND

Despite universal immunization programs, pertussis remains a major public health concern. This study aimed to describe the pertussis epidemiology in the Puglia region in 2006-2015 and to identify recent polymorphisms in Bordetella pertussis virulence-associated genes.

METHODS

The pertussis cases in 2006-2015 were identified from the National Hospital Discharge Database and the Information System of Infectious Diseases. Samples of pertussis cases in 2014-2016 that were confirmed by the Regional Reference Laboratory were subjected to ptxA, ptxP and prn gene sequencing and, in 10 cases, multiple-locus variable-number tandem repeat analysis.

RESULTS

In Puglia in 2006-2015, the pertussis incidence rose from an average of 1.39/100,000 inhabitants in 2006-2013 to 2.56-2.54/100,000 in 2014-2015. In infants <1 year of age, the incidence rose from an average of 60.4/100,000 infants in 2006-2013 to 149.9/100,000 in 2015. Of the 661 cases recorded in 2006-2015, 80.3% required hospitalization; of these, 45.4% were <1 year of age. Of the 80 sequenced samples, the allelic profile ptxA1-ptxP3-prn2 was detected in 74. This variant was detected in both vaccinated and unvaccinated people. Six Bordetella pertussis samples were prn deficient. The multiple-locus variable-number tandem repeat analysis cases exhibited multiple-locus variable-number tandem repeat analysis-type 27.

CONCLUSIONS

The pertussis incidence in Puglia has risen. The hypervirulent strain was also found in vaccinated people. This suggests bacterial adaptation to the vaccine and raises questions about acellular vaccine effectiveness. Prevention of infant pertussis cases is best achieved by immunizing the pregnant mother. Enhanced surveillance and systematic laboratory confirmation of pertussis should be improved in Italy.

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

One reason for increased pertussis incidence is the adaptation of Bordetella pertussis to vaccine-induced immunity by modulating its genomic structure. This study, EUpert IV, includes 265 isolates collected from nine European countries during 2012 to 2015 (n = 265) and compares the results to previous EUpert I to III studies (1998 to 2009). The analyses included genotyping, serotyping, pulsed-field gel electrophoresis (PFGE), and multilocus variable-number tandem-repeat analysis (MLVA). Genotyping results showed only small variations among the common virulence genes of B. pertussis The frequencies of serotypes Fim2 and Fim3 varied among the four collections. Genomic analyses showed that MLVA type 27 increased to 80% between the periods of 1998 to 2001 and 2012 to 2015. Two PFGE profiles, BpSR3 (29.4%) and BpSR10 (27.2%), constituted more than 50% of the circulating isolates in the present collection. Our study indicates that the European B. pertussis population is changing and became more homogenous after the introduction of acellular pertussis vaccines.

Proteomic Adaptation of Australian Epidemic Bordetella pertussis

Bordetella pertussis causes whooping cough. The predominant strains in Australia changed to single nucleotide polymorphism (SNP) cluster I (pertussis toxin promoter allele ptxP3/pertactin gene allele prn2) from cluster II (non-ptxP3/non-prn2). Cluster I was mostly responsible for the 2008-2012 Australian epidemic and was found to have higher fitness compared to cluster II using an in vivo mouse competition assay, regardless of host's immunization status. This study aimed to identify proteomic differences that explain higher fitness in cluster I using isobaric tags for relative and absolute quantification (iTRAQ), and high-resolution multiple reaction monitoring (MRM-hr). A few key differences in the whole cell and secretome were identified between the cluster I and II strains tested. In the whole cell, nine proteins were upregulated (>1.2 fold change, q < 0.05) and three were downregulated (<0.8 fold change, q < 0.05) in cluster I. One downregulated protein was BP1569, a TLR2 agonist for Th1 immunity. In the secretome, 12 proteins were upregulated and 1 was downregulated which was Bsp22, a type III secretion system (T3SS) protein. Furthermore, there was a trend of downregulation in three T3SS effectors and other virulence factors. Three proteins were upregulated in both whole cell and supernatant: BP0200, molybdate ABC transporter (ModB), and tracheal colonization factor A (TcfA). Important expression differences in lipoprotein, T3SS, and transport proteins between the cluster I and II strains were identified. These differences may affect immune evasion, virulence and metabolism, and play a role in increased fitness of cluster I.

Construction and evaluation of Bordetella pertussis live attenuated vaccine strain BPZE1 producing Fim3

Pertussis or whooping cough is currently the most prevalent vaccine-preventable childhood disease despite >85% global vaccination coverage. In recent years incidence has greatly increased in several high-income countries that have switched from the first-generation, whole-cell vaccine to the newer acellular vaccines, calling for improved vaccination strategies with better vaccines. We have developed a live attenuated pertussis vaccine candidate, called BPZE1, which is currently in clinical development. Unlike other pertussis vaccines, BPZE1 has been shown to provide strong protection against infection by the causative agent of pertussis, Bordetella pertussis, in non-human primates. BPZE1 is a derivative of the B. pertussis strain Tohama I, which produces serotype 2 (Fim2) but not serotype 3 fimbriae (Fim3). As immune responses to fimbriae are likely to contribute to protection, we constructed a BPZE1 derivative, called BPZE1f3, that produces both serotypes of fimbriae. Whereas nasal vaccination of mice with BPZE1 induced antibodies to Fim2 but not to Fim3, vaccination with BPZE1f3 elicited antibodies to both Fim2 and Fim3 at approximately the same level. In mice, both BPZE1 and BPZE1f3 provided equal levels of protection against clinical isolates that either produce Fim2 alone, both Fim2 and Fim3, or no fimbriae. However, vaccination with BPZE1f3 provided significantly stronger protection against Fim3-only producing B. pertussis than vaccination with BPZE1, indicating that immune responses to fimbriae contribute to serotype-specific protection against B. pertussis infection.

Significant Decrease in Pertactin-Deficient Bordetella pertussis Isolates, Japan

Prevalence of pertactin-lacking Bordetella pertussis isolates has been observed worldwide. In Japan, however, we found that the frequency of pertactin-deficient isolates in 2014–2016 (8%) was significantly lower than the frequency in 2005–2007 (41%), 2008–2010 (35%), and 2011–2013 (25%). This reduction was closely associated with changes in genotypes.

Bordetella Pertussis virulence factors in the continuing evolution of whooping cough vaccines for improved performance

Despite high vaccine coverage, whooping cough caused by Bordetella pertussis remains one of the most common vaccine-preventable diseases worldwide. Introduction of whole-cell pertussis (wP) vaccines in the 1940s and acellular pertussis (aP) vaccines in 1990s reduced the mortality due to pertussis. Despite induction of both antibody and cell-mediated immune (CMI) responses by aP and wP vaccines, there has been resurgence of pertussis in many countries in recent years. Possible reasons hypothesised for resurgence have ranged from incompliance with the recommended vaccination programmes with the currently used aP vaccine to infection with a resurged clinical isolates characterised by mutations in the virulence factors, resulting in antigenic divergence with vaccine strain, and increased production of pertussis toxin, resulting in dampening of immune responses. While use of these vaccines provide varying degrees of protection against whooping cough, protection against infection and transmission appears to be less effective, warranting continuation of efforts in the development of an improved pertussis vaccine formulations capable of achieving this objective. Major approaches currently under evaluation for the development of an improved pertussis vaccine include identification of novel biofilm-associated antigens for incorporation in current aP vaccine formulations, development of live attenuated vaccines and discovery of novel non-toxic adjuvants capable of inducing both antibody and CMI. In this review, the potential roles of different accredited virulence factors, including novel biofilm-associated antigens, of B. pertussis in the evolution, formulation and delivery of improved pertussis vaccines, with potential to block the transmission of whooping cough in the community, are discussed.

A National Seroepidemiologic Survey of Pertussis Among School Children in Taiwan

BACKGROUND

In 2009, a booster dose of acellular pertussis vaccine for children at or before entry to elementary school was added to the national immunization program in Taiwan, which includes pertussis vaccination at 2, 4, 6 and 18 months of age. In 2013, a study to assess the level of humoral immunity against pertussis in elementary and junior high school children and adolescents was conducted.

METHODS

A multistage stratified systematic sampling method was applied to randomly selected grade 1 to 9 school children for testing. Serum samples were tested for IgG antibodies to Bordetella pertussis using commercial enzyme-linked immunosorbent assay kits. The study collected information on sociodemographic characteristics, vaccination history, sibling number and disease history of pertussis.

RESULTS

The study recruited 2782 school children from 58 schools around the country. By questionnaire, only 1% (28/2782) students had history of pertussis. The overall positivity rate of anti-B. pertussis IgG was 42.5%, and the rates were not different between the 5 geographical areas (range from 39.6% to 44.6%, P = 0.375). Age-stratified data showed that the positivity rates were 43.6-48.8% among grade 1-3 students, 26.6-28.7% in grade 4-5 students and increased progressively from 39.4% to 51.3% in grade 6-9 students. The overall positivity rate was significantly higher in the nonbooster group (46.4% versus 38.6%, P < 0.01).

CONCLUSION

The prevalence of anti-B. pertussis antibody was 42.5% in grade 1-9 students under the current vaccination program in Taiwan. Antibody induced by the booster vaccination before entry of primary school waned rapidly in 3-4 years. Rapid waning of anti-B. pertussis antibody may explain the resurgence of whooping cough in recent decades. Additional booster doses should be considered in adolescents and adults.

Hyperbiofilm Formation by Bordetella pertussis Strains Correlates with Enhanced Virulence Traits

Pertussis, or whooping cough, caused by the obligate human pathogen Bordetella pertussis is undergoing a worldwide resurgence. The majority of studies of this pathogen are conducted with laboratory-adapted strains which may not be representative of the species as a whole. Biofilm formation by B. pertussis plays an important role in pathogenesis. We conducted a side-by-side comparison of the biofilm-forming abilities of the prototype laboratory strains and the currently circulating isolates from two countries with different vaccination programs. Compared to the reference strain, all strains examined herein formed biofilms at high levels. Biofilm structural analyses revealed country-specific differences, with strains from the United States forming more structured biofilms. Bacterial hyperaggregation and reciprocal expression of biofilm-promoting and -inhibitory factors were observed in clinical isolates. An association of increased biofilm formation with augmented epithelial cell adhesion and higher levels of bacterial colonization in the mouse nose and trachea was detected. To our knowledge, this work links for the first time increased biofilm formation in bacteria with a colonization advantage in an animal model. We propose that the enhanced biofilm-forming capacity of currently circulating strains contributes to their persistence, transmission, and continued circulation.

Bordetella pertussis: new concepts in pathogenesis and treatment

PURPOSE OF REVIEW

The purpose of this review is to summarize and discuss recent findings and selected topics of interest in Bordetella pertussis virulence and pathogenesis and treatment of pertussis. It is not intended to cover issues on immune responses to B. pertussis infection or problems with currently used pertussis vaccines.

RECENT FINDINGS

Studies on the activities of various B. pertussis virulence factors include the immunomodulatory activities of filamentous hemagglutinin, fimbriae, and adenylate cyclase toxin. Recently emerging B. pertussis strains show evidence of genetic selection for vaccine escape mutants, with changes in vaccine antigen-expressing genes, some of which may have increased the virulence of this pathogen. Severe and fatal pertussis in young infants continues to be a problem, with several studies highlighting predictors of fatality, including the extreme leukocytosis associated with this infection. Treatments for pertussis are extremely limited, though early antibiotic intervention may be beneficial. Neutralizing pertussis toxin activity may be an effective strategy, as well as targeting two host proteins, pendrin and sphingosine-1-phosphate receptors, as novel potential therapeutic interventions.

SUMMARY

Pertussis is reemerging as a major public health problem and continued basic research is revealing information on bacterial virulence and disease pathogenesis, as well as potential novel strategies for vaccination and targets for therapeutic intervention.

Acquisition of C1 inhibitor by Bordetella pertussis virulence associated gene 8 results in C2 and C4 consumption away from the bacterial surface

Whooping cough, or pertussis, is a contagious disease of the respiratory tract that is re-emerging worldwide despite high vaccination coverage. The causative agent of this disease is the Gram-negative Bordetella pertussis. Knowledge on complement evasion strategies of this pathogen is limited. However, this is of great importance for future vaccine development as it has become apparent that a novel pertussis vaccine is needed. Here, we unravel the effect of Virulence associated gene 8 (Vag8) of B. pertussis on the human complement system at the molecular level. We show that both recombinant and endogenously secreted Vag8 inhibit complement deposition on the bacterial surface at the level of C4b. We reveal that Vag8 binding to human C1-inhibitor (C1-inh) interferes with the binding of C1-inh to C1s, C1r and MASP-2, resulting in the release of active proteases that subsequently cleave C2 and C4 away from the bacterial surface. We demonstrate that the depletion of these complement components in the bacterial surrounding and subsequent decreased deposition on B. pertussis leads to less complement-mediated bacterial killing. Vag8 is the first protein described that specifically prevents C1s, C1r and MASP-2 binding to C1-inh and thereby mediates complement consumption away from the bacterial surface. Unravelling the mechanism of this unique complement evasion strategy of B. pertussis is one of the first steps towards understanding the interactions between the first line of defense complement and B. pertussis.

Despite wide-spread vaccination, whooping cough caused by the Gram-negative bacterium Bordetella pertussis remains a public health problem and has been re-emerging in the past decades. To this end, new vaccination strategies are being explored including the use of complement evasion molecules as vaccine candidates. Autotransporter Virulence associated gene 8 (Vag8) was previously shown to be involved in complement evasion. However, the molecular mechanism of this immune evasion was not understood. Considering knowledge on molecular mechanisms is crucial for further studies regarding vaccine development, we investigated the underlying mechanism of Vag8 induced complement evasion of B. pertussis. We show that both recombinant Vag8 as well as endogenously secreted Vag8 inhibits complement activation via the classical and lectin complement pathway at the level of C4 and C2. We identified a novel bacterial complement evasion strategy initiated by the binding of Vag8 to C1-inhibitor. This binding interferes with the interactions between C1-inhibitor and the proteases C1s, C1r and MASP-2 resulting in the release of active proteases that cleave C4 and C2 away from the bacterial surface. This environmental consumption of C4 and C2 leads to decreased complement deposition on the bacterial surface and hence inhibits complement-mediated killing of B. pertussis.

Bordetella pertussis

Pertussis is a highly infectious vaccine-preventable cough illness that continues to be a significant source of morbidity and mortality around the world. The majority of human illness is caused by Bordetella pertussis, and some is caused by Bordetella parapertussis. Bordetella is a Gram-negative, pleomorphic, aerobic coccobacillus. In the past several years, even countries with high immunization rates in early childhood have experienced rises in pertussis cases. Reasons for the resurgence of reported pertussis may include molecular changes in the organism and increased awareness and diagnostic capabilities, as well as lessened vaccine efficacy and waning immunity. The most morbidity and mortality with pertussis infection is seen in infants too young to benefit from immunization. Severe infection requiring hospitalization, including in an intensive care setting, is mostly seen in those under 3 months of age. As a result, research and public health actions have been aimed at better understanding and reducing the spread of Bordetella pertussis. Studies comparing the cost benefit of cocooning strategies versus immunization of pregnant women have been favorable towards immunizing pregnant women. This strategy is expected to prevent a larger number of pertussis cases, hospitalizations, and deaths in infants <1 year old while also being cost-effective. Studies have demonstrated that the source of infection in infants usually is a family member. Efforts to immunize children and adults, in particular pregnant women, need to remain strong.

Lung CD4 Tissue-Resident Memory T Cells Mediate Adaptive Immunity Induced by Previous Infection of Mice with Bordetella pertussis

Th1 and Th17 cells have an established role in protective immunity to Bordetella pertussis, but this evidence is based largely on peripheral T cells. There is emerging evidence that local tissue-resident memory T (T_RM) cells that accumulate in tissue following mucosal infection may be crucial for long-term immunity. In this study, we examined the role of respiratory CD4 T_RM cells in immunity to B. pertussis Natural immunity to B. pertussis induced by infection is considered long lasting and effective at preventing reinfection. Consistent with this, we found that convalescent mice rapidly cleared the bacteria after reinfection. Furthermore, CD4 T cells with a T_RM cell phenotype (CD44⁺CD62L^-CD69⁺ or CD44⁺CD62L^-CD69⁺CD103⁺) accumulated in the lungs of mice during infection with B. pertussis and significantly expanded through local proliferation following reinfection. These CD4 T_RM cells were B. pertussis specific and secreted IL-17 or IL-17 and IFN-γ. Treatment of mice with FTY720, which prevented migration of T and B cells from lymph nodes to the circulation, significantly exacerbated B. pertussis infection. This was associated with significantly reduced infiltration of central memory T cells and B cells into the lungs. However, the local expansion of T_RM cells and the associated rapid clearance of the secondary infection were not affected by treatment with FTY720 before rechallenge. Moreover, adoptive transfer of lung CD4 T_RM cells conferred protection in naive mice. Our findings reveal that Ag-specific CD4 T_RM cells play a critical role in adaptive immunity against reinfection and memory induced by natural infection with B. pertussis.

Development of a qualitative assay for screening of Bordetella pertussis isolates for pertussis toxin production

Bordetella pertussis infection has been increasing in the US, with reported cases reaching over 50,000 in 2012, a number last observed in the 1950s. Concurrently, B. pertussis lacking the pertactin protein, one of the immunogens included in the acellular vaccine formulations, has rapidly emerged since 2010, and has become the predominant circulating phenotype. Monitoring the production of the remaining acellular vaccine immunogens, such as pertussis toxin (Pt), is a critical next step. To date, methods for screening Pt have been either through genomic sequencing means or by conventional ELISAs. However, sequencing limits detection to the DNA level, missing potential disruptions in transcription or translation. Conventional ELISAs are beneficial for detecting the protein; however, they can often suffer from poor sensitivity and specificity. Here we describe a rapid, highly sensitive and specific electrochemiluminescent capture ELISA that can detect Pt production in prepared inactivated bacterial suspensions. Over 340 isolates were analyzed and analytical validation parameters, such as precision, reproducibility, and stability, were rigorously tested. Intra-plate and inter-plate variability measured at 9.8% and 11.5%, respectively. Refrigerated samples remained stable for two months and variability was unaffected (coefficient of variation was 12%). Interestingly, despite the intention of being a qualitative method, the assay was sensitive enough to detect a small, but statistically significant, difference in protein production between different pertussis promoter allelic groups of strains, ptxP1 and ptxP3. This technology has the ability to perform screening of multiple antigens at one time, thus, improving testing characteristics while minimizing costs, specimen volume, and testing time.

Assessing the social and environmental determinants of pertussis epidemics in Queensland, Australia: a Bayesian spatio-temporal analysis

Pertussis epidemics have displayed substantial spatial heterogeneity in countries with high socioeconomic conditions and high vaccine coverage. This study aims to investigate the relationship between pertussis risk and socio-environmental factors on the spatio-temporal variation underlying pertussis infection. We obtained daily case numbers of pertussis notifications from Queensland Health, Australia by postal area, for the period January 2006 to December 2012. A Bayesian spatio-temporal model was used to quantify the relationship between monthly pertussis incidence and socio-environmental factors. The socio-environmental factors included monthly mean minimum temperature (MIT), monthly mean vapour pressure (VAP), Queensland school calendar pattern (SCP), and socioeconomic index for area (SEIFA). An increase in pertussis incidence was observed from 2006 to 2010 and a slight decrease from 2011 to 2012. Spatial analyses showed pertussis incidence across Queensland postal area to be low and more spatially homogeneous during 2006-2008; incidence was higher and more spatially heterogeneous after 2009. The results also showed that the average decrease in monthly pertussis incidence was 3·1% [95% credible interval (CrI) 1·3-4·8] for each 1 °C increase in monthly MIT, while average increase in monthly pertussis incidences were 6·2% (95% CrI 0·4-12·4) and 2% (95% CrI 1-3) for SCP periods and for each 10-unit increase in SEIFA, respectively. This study demonstrated that pertussis transmission is significantly associated with MIT, SEIFA, and SCP. Mapping derived from this work highlights the potential for future investigation and areas for focusing future control strategies.

The History of Bordetella pertussis Genome Evolution Includes Structural Rearrangement

Despite high pertussis vaccine coverage, reported cases of whooping cough (pertussis) have increased over the last decade in the United States and other developed countries. Although Bordetella pertussis is well known for its limited gene sequence variation, recent advances in long-read sequencing technology have begun to reveal genomic structural heterogeneity among otherwise indistinguishable isolates, even within geographically or temporally defined epidemics. We have compared rearrangements among complete genome assemblies from 257 B. pertussis isolates to examine the potential evolution of the chromosomal structure in a pathogen with minimal gene nucleotide sequence diversity. Discrete changes in gene order were identified that differentiated genomes from vaccine reference strains and clinical isolates of various genotypes, frequently along phylogenetic boundaries defined by single nucleotide polymorphisms. The observed rearrangements were primarily large inversions centered on the replication origin or terminus and flanked by IS481, a mobile genetic element with >240 copies per genome and previously suspected to mediate rearrangements and deletions by homologous recombination. These data illustrate that structural genome evolution in B. pertussis is not limited to reduction but also includes rearrangement. Therefore, although genomes of clinical isolates are structurally diverse, specific changes in gene order are conserved, perhaps due to positive selection, providing novel information for investigating disease resurgence and molecular epidemiology.IMPORTANCE Whooping cough, primarily caused by Bordetella pertussis, has resurged in the United States even though the coverage with pertussis-containing vaccines remains high. The rise in reported cases has included increased disease rates among all vaccinated age groups, provoking questions about the pathogen's evolution. The chromosome of B. pertussis includes a large number of repetitive mobile genetic elements that obstruct genome analysis. However, these mobile elements facilitate large rearrangements that alter the order and orientation of essential protein-encoding genes, which otherwise exhibit little nucleotide sequence diversity. By comparing the complete genome assemblies from 257 isolates, we show that specific rearrangements have been conserved throughout recent evolutionary history, perhaps by eliciting changes in gene expression, which may also provide useful information for molecular epidemiology.

Modelling the evolution of HIV-1 virulence in response to imperfect therapy and prophylaxis

Average HIV-1 virulence appears to have evolved in different directions in different host populations since antiretroviral therapy first became available, and models predict that HIV drugs can select for either higher or lower virulence, depending on how treatment is administered. However, HIV virulence evolution in response to "leaky" therapy (treatment that imperfectly suppresses viral replication) and the use of preventive drugs (pre-exposure prophylaxis) has not been explored. Using adaptive dynamics, we show that higher virulence can evolve when antiretroviral therapy is imperfectly effective and that this evolution erodes some of the long-term clinical and epidemiological benefits of HIV treatment. The introduction of pre-exposure prophylaxis greatly reduces infection prevalence, but can further amplify virulence evolution when it, too, is leaky. Increasing the uptake rate of these imperfect interventions increases selection for higher virulence and can lead to counterintuitive increases in infection prevalence in some scenarios. Although populations almost always fare better with access to interventions than without, untreated individuals could experience particularly poor clinical outcomes when virulence evolves. These findings predict that antiretroviral drugs may have underappreciated evolutionary consequences, but that maximizing drug efficacy can prevent this evolutionary response. We suggest that HIV virulence evolution should be closely monitored as access to interventions continues to improve.

Emerging Bordetella pertussis Strains Induce Enhanced Signaling of Human Pattern Recognition Receptors TLR2, NOD2 and Secretion of IL-10 by Dendritic Cells

Vaccines against pertussis have been available for more than 60 years. Nonetheless, this highly contagious disease is reemerging even in countries with high vaccination coverage. Genetic changes of Bordetella pertussis over time have been suggested to contribute to the resurgence of pertussis, as these changes may favor escape from vaccine-induced immunity. Nonetheless, studies on the effects of these bacterial changes on the immune response are limited. Here, we characterize innate immune recognition and activation by a collection of genetically diverse B. pertussis strains isolated from Dutch pertussis patients before and after the introduction of the pertussis vaccines. For this purpose, we used HEK-Blue cells transfected with human pattern recognition receptors TLR2, TLR4, NOD2 and NOD1 as a high throughput system for screening innate immune recognition of more than 90 bacterial strains. Physiologically relevant human monocyte derived dendritic cells (moDC), purified from peripheral blood of healthy donors were also used. Findings indicate that, in addition to inducing TLR2 and TLR4 signaling, all B. pertussis strains activate the NOD-like receptor NOD2 but not NOD1. Furthermore, we observed a significant increase in TLR2 and NOD2, but not TLR4, activation by strains circulating after the introduction of pertussis vaccines. When using moDC, we observed that the recently circulating strains induced increased activation of these cells with a dominant IL-10 production. In addition, we observed an increased expression of surface markers including the regulatory molecule PD-L1. Expression of PD-L1 was decreased upon blocking TLR2. These in vitro findings suggest that emerging B. pertussis strains have evolved to dampen the vaccine-induced inflammatory response, which would benefit survival and transmission of this pathogen. Understanding how this disease has resurged in a highly vaccinated population is crucial for the design of improved vaccines against pertussis.

The Pertussis resurgence: putting together the pieces of the puzzle

Pertussis incidence is rising in almost every country where acellular pertussis (aP) vaccines have been introduced, and is occurring across all age groups from infancy to adulthood. The key question is why? While several known factors such as waning of immunity, detection bias due to more sensitive tests and higher awareness of the disease among practitioners, and evolutionary shifts among B. pertussis all likely contribute, collectively, these do not adequately explain the existing epidemiologic data, suggesting that additional factors also contribute. Key amongst these is recent data indicating that the immune responses induced by aP vaccines differ fundamentally from those induced by the whole cell pertussis (wP) vaccines, and do not lead to mucosal immunity. If so, it appears likely that differences in how the two categories of vaccines work, may be pivotal to our overall understanding of the pertussis resurgence.

Evaluation of a commercial loop-mediated isothermal amplification assay for diagnosis of Bordetella pertussis infection

We evaluated a commercial loop-mediated isothermal amplification (LAMP) assay kit for Bordetella pertussis detection. The LAMP primers were designed to target the ptxP1 allele of the pertussis toxin promoter, but the assay could detect B. pertussis ptxP3 and ptxP8 strains in addition to ptxP1 strains, with high analytical sensitivity.

The pertussis enigma: reconciling epidemiology, immunology and evolution

Pertussis, a highly contagious respiratory infection, remains a public health priority despite the availability of vaccines for 70 years. Still a leading cause of mortality in developing countries, pertussis has re-emerged in several developed countries with high vaccination coverage. Resurgence of pertussis in these countries has routinely been attributed to increased awareness of the disease, imperfect vaccinal protection or high infection rates in adults. In this review, we first present 1980-2012 incidence data from 63 countries and show that pertussis resurgence is not universal. We further argue that the large geographical variation in trends probably precludes a simple explanation, such as the transition from whole-cell to acellular pertussis vaccines. Reviewing available evidence, we then propose that prevailing views on pertussis epidemiology are inconsistent with both historical and contemporary data. Indeed, we summarize epidemiological evidence showing that natural infection and vaccination both appear to provide long-term protection against transmission and disease, so that previously infected or vaccinated adults contribute little to overall transmission at a population level. Finally, we identify several promising avenues that may lead to a consistent explanation of global pertussis epidemiology and to more effective control strategies.