Factors contributing to pertussis resurgence

Antibody avidity to pertussis toxin after acellular pertussis vaccination and infection

Pertussis toxin (PT) is a unique virulence factor of Bordetella pertussis, and therefore a key component of acellular pertussis vaccines. Although immunity after infection seems to persist longer than after vaccination, the exact mechanisms are not fully known. In this study the overall binding strength (avidity) of anti-PT IgG antibodies was compared after acellular booster vaccination and infection, as a parameter to evaluate long-lasting protection.Danish and Finnish serum samples from a total of 134 serologically confirmed patients and 112 children who received acellular booster vaccines were included in this study. The concentration of anti-PT IgG was first determined by ELISA, followed by two separate ELISAs to evaluate antibody avidity: either with a dilution series of urea as a bond-breaking agent of antibody and antigen binding and a constant anti-PT IgG concentration between the samples or with a constant dilution ratio of sera and detergent. In addition to urea, the use of diethylamine and ammonium thiocyanate as disruptive agents were first compared between each other.A strong Spearman correlation (R > 0.801) was noted between avidity and concentration of anti-PT IgG antibodies if a constant serum dilution method was used, and avidity was noted to be higher in patients in comparison to vaccinees in Denmark, but not in Finland. However, no correlation between antibody concentration and avidity was found if a constant anti-PT IgG concentration was used (R = -0.157). With this method, avidity after vaccination was significantly higher in comparison to that after infection in both Danish and Finnish subjects (p < 0.01). A shorter time since the latest booster vaccination was found to affect avidity positively on the next PT-antigen exposure with either vaccination or infection.

Characterization of Bordetella pertussis Strains Isolated from India

Despite high level vaccination and the availability of two different types of vaccines, whole cell (wP) and acellular vaccines (aP), the resurgence of pertussis has been reported in many countries. Antigenic variation within circulating and vaccine strains is the most documented reason reported for the resurgence of pertussis. Research on genetic divergence among circulating and vaccine strains has largely been reported in countries using aP vaccines. There are inadequate data available for antigenic variation in B. pertussis from wP-using countries. India has used wP for more than 40 years in their primary immunization program. The present study reports five clinical isolates of B. pertussis from samples of pediatric patients with pertussis symptoms observed in India. Genotypic and phenotypic characterization of clinical isolates were performed by serotyping, genotyping, whole genome analyses and comparative genomics. All clinical isolates showed serotype 1, 2 and 3 based on the presence of fimbriae 2 and 3. Genotyping showed genetic similarities in allele types for five aP genes within vaccine strains and clinical isolates reported from India. The presence of the ptxP3 genotype was observed in two out of five clinical isolates. Whole-genome sequencing was performed for clinical isolates using the hybrid strategy of combining Illumina (short reads) and oxford nanopore (long reads) sequencing strategies. Clinical isolates (n = 5) and vaccine strains (n = 7) genomes of B. pertussis from India were compared with 744 B. pertussis closed genomes available in the public databases. The phylogenomic comparison of B. pertussis genomes reported from India will be advantageous in better understanding pertussis resurgence reported globally with respect to pathogen adaptation.

Diphtheria-tetanus-pertussis vaccine: past, current & future

The diphtheria-tetanus-pertussis (DTP) vaccine can prevent diphtheria, tetanus and pertussis. The component antigens of the DTP vaccine had long been monovalent vaccines. The pertussis vaccine was licensed in 1914. The same year, the mixtures of diphtheria toxin and antitoxin were put into use. In 1926, alum-precipitated diphtheria toxoid was registered, and in 1937 adsorbed tetanus toxoid was put on the market. The development of numerous effective DTP vaccines quickly stimulated efforts to combine DTP with other routine vaccines for infants. This overview covers the most important information regarding the invention of DTP vaccines, their modifications and the needs that should be focused on in the future.

Effectiveness of experimental and commercial pertussis vaccines in the elimination of Bordetella pertussis isolates with different genetic profiles in murine model

The aim of this study was to compare the elimination of Bordetella pertussis clinical isolates, representing different genotypes in relation to alleles encoding virulence factors (MLST-multi-locus antigen sequence typing), MLVA type (multi-locus variable-number tandem repeat analysis) and PFGE group (pulsed-field gel electrophoresis) from the lungs of naive mice or mice were immunised with the commercial whole-cell pertussis vaccine, the acellular pertussis vaccine and the experimental whole-cell pertussis vaccine. Molecular data indicate that the resurgence of pertussis in populations with high vaccine coverage is associated with genomic adaptation of B. pertussis, to vaccine selection pressure. Pertactin-negative B. pertussis isolates were suspected to contribute to the reduced vaccine effectiveness. It was shown that one of the isolates used is PRN deficient. The mice were intranasally challenged with bacterial suspension containing approximately 5 × 10 7 CFU/ml B. pertussis. The immunogenicity of the tested vaccines against PT (pertussis toxin), PRN (pertactin), FHA (filamentous haemagglutinin) and FIM (fimbriae types 2 and 3) was examined. The commercial whole-cell and acellular pertussis vaccines induced an immunity effective at eliminating the genetically different B. pertussis isolates from the lungs. However, the elimination of the PRN-deficient isolate from the lungs of mice vaccinated with commercial vaccines was delayed as compared to the PRN ( +) isolate, suggesting phenotypic differences with the circulating isolates and vaccine strains. The most effective vaccine was the experimental vaccine with the composition identical to that of the strains used for infection.

Evaluation of Outer Membrane Vesicles Obtained from Predominant Local Isolate of Boredetella pertussis as a Vaccine Candidate

Background:

Pertussis is a current contagious bacterial disease caused by Bp. Given the prevalence of pertussis, development of new vaccines is important. This study was attempted to evaluate the expression of main virulence factors (PTX, PRN, and FHA) from Bp predominant strains and also compare the expression of these factors in the OMVs obtained from predominant circulating Bp isolate.

Methods:

The physicochemical features of the prepared OMVs were analyzed by electron microscopy and SDS-PAGE. The presence of the mentioned virulence factors was confirmed by Western blotting. BALB/c mice (n = 21) immunized with characterized OMVs were challenged intranasally with sublethal doses of Bp, to examine their protective capacity.

Results:

Electron microscopic examination of the OMVs indicated vesicles within the range of 40 to 200 nm. SDS-PAGE and Western blotting demonstrated the expression of all three main protective immunogens (PTX, PRN, and FHA), prevalent in the predominant, challenge, and vaccine strains, and OMVs of the predominant IR37 strain and BP134 vaccine strain. Significant differences were observed in lung bacterial counts between the immunized mice with OMV (30 CFU/lung) compared to the negative control group ((6 10⁴ CFU/lung; p < 0.001). In mice immunized with OMVs (3 µg), the number of lungs recovered colonies after five days dropped at least five orders of magnitude compared to the control group.

Conclusion:

OMVs obtained from circulating isolates with the predominant profile may constitute a highly promising vaccine quality. They also can be proposed as a potential basic material for the development of new pertussis vaccine candidate.

Fha Deficient Bordetella pertussis Isolates in Iran with 50 Years Whole Cell Pertussis Vaccination

Background:

Bordetella pertussis, a highly contagious respiratory. Notably, the resurgence of pertussis has recently been associated with the lacking production of vaccine virulence factors. This study aimed to screen pertactin (Prn) and filamentous hemagglutinin (Fha) production in Iran with 50 years’ whole cell vaccine (WCV) immunization program.

Methods:

Overall, 130 B. pertussis isolates collected from Pertussis Reference Laboratory of Iran during 2005–2018. Real-time PCR was performed by targeting IS481, ptxP, IS1001 and IS1002 for species confirmation of B. pertussis. Western-blot was used to evaluate the expression of virulence factors (pertactin and filamentous hemagglutinin).

Results:

All tested B. pertussis isolates expressed Prn and all except two isolates expressed Fha. We have sequenced genomes of these strains and identified differences compared with genome reference B. pertussis Tohama I.

Conclusion:

Many countries reporting Prn and Fha-deficiency due to acellular vaccine (ACV) pressure. Our results demonstrate in a country with WCV history, Fha-deficient isolates may rise independently. However, Prn-deficient isolates are more under the ACV pressure in B. pertussis isolates. Continues surveillance will provide a better understanding of the effect of WCV on the evolution of the pathogen deficiency.

Asymptomatic Bordetella pertussis infections in a longitudinal cohort of young African infants and their mothers

Recent pertussis resurgence in numerous countries may be driven by asymptomatic infections. Most pertussis surveillance studies are cross-sectional and cannot distinguish asymptomatic from pre-symptomatic infections. Longitudinal surveillance could overcome this barrier, providing more information about the true burden of pertussis at the population level. Here we analyze 17,442 nasopharyngeal samples from a longitudinal cohort of 1320 Zambian mother/infant pairs. Our analysis has two elements. First, we demonstrate that the full range of IS481 qPCR CT values provides insight into pertussis epidemiology, showing concordance of low and high CT results over time, within mother/infant pairs, and in relation to symptomatology. Second, we exploit these full-range qPCR data to demonstrate a high incidence of asymptomatic pertussis, including among infants. Our results demonstrate a wider burden of pertussis infection than we anticipated in this population, and expose key limitations of threshold-based interpretation of qPCR results in infectious disease surveillance.

Asymptomatic Bordetella pertussis infections in young African infants and their mothers identified within a longitudinal cohort

Despite long-standing vaccination programs, pertussis incidence has increased in numerous countries; transmission by asymptomatic individuals is a suspected driver of this resurgence. However, unequivocal evidence documenting asymptomatic infections in adults and children is lacking due, in part, to the cross-sectional nature of most pertussis surveillance studies. In addition, modern pertussis surveillance relies on quantitative PCR (qPCR) using fixed diagnostic thresholds to identify cases. To address this gap, we present a longitudinal analysis of 17,442 nasopharyngeal samples collected from a cohort of 1,320 Zambian mother/infant pairs. Using full-range cycle threshold (CT) values from IS481 qPCR assays, we document widespread asymptomatic infections among mothers and also, surprisingly, among young infants. From an initial group of eight symptomatic infants who tested positive by qPCR, we identify frequent contemporaneous subclinical infections in mothers. Within the full cohort, we observe strong temporal correlation between low- and high-intensity qPCR signals. We compute a single time-averaged score for each individual summarizing the evidence for pertussis infection (EFI), and show that EFI strongly clusters within mother/infant pairs, and is strongly associated with clinical symptomatology and antibiotic use. Overall, the burden of pertussis here is substantially underestimated when restricting diagnostic criteria to IS481 CT≤35. Rather, we find that full-range CT values provide valuable insights into pertussis epidemiology in this population, and illuminate the infection arc within individuals. These findings have significant implications for quantifying asymptomatic pertussis prevalence and its contribution to overall transmission. Our results also expose limitations of threshold-based interpretations of qPCR assays in infectious disease surveillance.

Comparative genomics of whole-cell pertussis vaccine strains from India

BACKGROUND

Despite high vaccination coverage using acellular (ACV) and whole-cell pertussis (WCV) vaccines, the resurgence of pertussis is observed globally. Genetic divergence in circulating strains of Bordetella pertussis has been reported as one of the contributing factors for the resurgence of the disease. Our current knowledge of B. pertussis genetic evolution in circulating strains is mostly based on studies conducted in countries using ACVs targeting only a few antigens used in the production of ACVs. To better understand the adaptation to vaccine-induced selection pressure, it will be essential to study B. pertussis populations in developing countries which are using WCVs. India is a significant user and global supplier of WCVs. We report here comparative genome analyses of vaccine and clinical isolates reported from India. Whole-genome sequences obtained from vaccine strains: WCV (J445, J446, J447 and J448), ACV (BP165) were compared with Tohama-I reference strain and recently reported clinical isolates from India (BPD1, BPD2). Core genome-based phylogenetic analysis was also performed using 166 isolates reported from countries using ACV.

RESULTS

Whole-genome analysis of vaccine and clinical isolates reported from India revealed high genetic similarity and conserved genome among strains. Phylogenetic analysis showed that clinical and vaccine strains share genetic closeness with reference strain Tohama-I. The allelic profile of vaccine strains (J445:ptxP1/ptxA2/prn1/fim2-1/fim3-1; J446: ptxP2/ptxA4/prn7/fim2-2/fim3-1; J447 and J448: ptxP1/ptxA1/ prn1/fim2-1/fim3-1), which matched entirely with clinical isolates (BPD1:ptxP1/ptxA1/prn1/fim2-1 and BPD2: ptxP1/ptxA1/prn1/fim2-1) reported from India. Multi-locus sequence typing (MLST) demonstrated the presence of dominant sequence types ST2 and primitive ST1 in vaccine strains which will allow better coverage against circulating strains of B. pertussis.

CONCLUSIONS

The study provides a detailed characterization of vaccine and clinical strains reported from India, which will further facilitate epidemiological studies on genetic shifts in countries which are using WCVs in their immunization programs.

Use of a Neonatal-Mouse Model to Characterize Vaccines and Strategies for Overcoming the High Susceptibility and Severity of Pertussis in Early Life

Newborns and unvaccinated infants, compared to other age groups, are more susceptible to pertussis infection, manifesting severe symptoms leading to a higher mortality. The recent increase in pertussis cases demands more effective strategies to overcome this major health problem. In parallel with maternal-immunization, neonatal-immunization (NI) is a strategy needing revision. Here, using the intranasal-challenge-mouse-model we evaluated the protective capacity of NI in both naïve-mice and those with maternally acquired immunity. We tested our acellular-vaccine-candidate based on outer-membrane-vesicles derived from Bordetella pertussis (OMVP) that induces Th2-profile but also the recommended Th-profile for protection: Th1/Th17-profile and CD4 T-memory-cells that reside in the lungs. Commercial acellular-vaccine (aP) and whole cell-vaccine (wP) inducing mainly Th2-profile and Th1-profile, respectively, were also tested. Analyzing the induced immunity and protection capability of NI included in 1- or 2-dose schedules with the same or different types of vaccine, we detected that the aP-vaccine administered in either single- or 2-dose schedules protected against sublethal B. pertussis infection. Schedules consisting of doses of aP neonatally and of OMVP or wP vaccine during infancy greatly reduced bacterial lung colonization while inducing the highest levels of high-avidity anti-pertussis toxin (PTx) IgG. That OMVP or wP neonatal dose did not interfere with the protection of transferred maternal immunity was especially encouraging. Moreover, OMVP- or wP used as a neonatal dose enhanced the quality of the humoral immune response in immunized pups. Antibodies generated by OMVP-or wP-vaccinated mice born to aP-immunized mothers were of higher avidity than those from mice that harbored only maternal immunity; but when mothers and neonates were immunized with the same aP-vaccine, the humoral response in the neonates was partially suppressed through the blunting of the level of anti-PTx IgG induced by the neonatal aP dose. These results demonstrated that neonatal immunization is a possible strategy to be considered to improve the current pertussis epidemiology. For neonates without maternal-immunity, mixed-vaccination schedules that include the aP- and OMVP-vaccines appear to be the most appropriate to induce protection in the pups. For offspring from immune mothers, to avoid blunting-effect, NI should be carried out with vaccines other than those applied during pregnancy.

Estimating seasonal variation in Australian pertussis notifications from 1991 to 2016: evidence of spring to summer peaks

Unlike for many other respiratory infections, the seasonality of pertussis is not well understood. While evidence of seasonal fluctuations in pertussis incidence has been noted in some countries, there have been conflicting findings including in the context of Australia. We investigated this issue by analysing the seasonality of pertussis notifications in Australia using monthly data from January 1991 to December 2016. Data were made available for all states and territories in Australia except for the Australian Capital Territory and were stratified into age groups. Using a time-series decomposition approach, we formulated a generalised additive model where seasonality is expressed using cosinor terms to estimate the amplitude and peak timing of pertussis notifications in Australia. We also compared these characteristics across different jurisdictions and age groups. We found evidence that pertussis notifications exhibit seasonality, with peaks observed during the spring and summer months (November–January) in Australia and across different states and territories. During peak months, notifications are expected to increase by about 15% compared with the yearly average. Peak notifications for children <5 years occurred 1–2 months later than the general population, which provides support to the theory that older household members remain an important source of pertussis infection for younger children. In addition, our results provide a more comprehensive spatial picture of seasonality in Australia, a feature lacking in previous studies. Finally, our findings suggest that seasonal forcing may be useful to consider in future population transmission models of pertussis.

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.

A Pertussis Outer Membrane Vesicle-Based Vaccine Induces Lung-Resident Memory CD4 T Cells and Protection Against Bordetella pertussis, Including Pertactin Deficient Strains

Pertussis is a respiratory infectious disease that has been resurged during the last decades. The change from the traditional multi-antigen whole-cell pertussis (wP) vaccines to acellular pertussis (aP) vaccines that consist of a few antigens formulated with alum, appears to be a key factor in the resurgence of pertussis in many countries. Though current aP vaccines have helped to reduce the morbidity and mortality associated with pertussis, they do not provide durable immunity or adequate protection against the disease caused by the current circulating strains of Bordetella pertussis, which have evolved in the face of the selection pressure induced by the vaccines. Based on the hypothesis that a new vaccine containing multiple antigens could overcome deficiencies in the current aP vaccines, we have designed and characterized a vaccine candidate based on outer membrane vesicle (OMVs). Here we show that the OMVs vaccine, but not an aP vaccine, protected mice against lung infection with a circulating pertactin (PRN)-deficient isolate. Using isogenic bacteria that in principle only differ in PRN expression, we found that deficiency in PRN appears to be largely responsible for the failure of the aP vaccine to protect against this circulating clinical isolates. Regarding the durability of induced immunity, we have already reported that the OMV vaccine is able to induce long-lasting immune responses that effectively prevent infection with B. pertussis. Consistent with this, here we found that CD4 T cells with a tissue-resident memory (T_RM) cell phenotype (CD44⁺CD62L^lowCD69⁺ and/or CD103⁺) accumulated in the lungs of mice 14 days after immunization with 2 doses of the OMVs vaccine. CD4 T_RM cells, which have previously been shown to play a critical role sustained protective immunity against B. pertussis, were also detected in mice immunized with wP vaccine, but not in the animals immunized with a commercial aP vaccine. The CD4 T_RM cells secreted IFN-γ and IL-17 and were significantly expanded through local proliferation following respiratory challenge of mice with B. pertussis. Our findings that the OMVs vaccine induce respiratory CD4 T_RM cells may explain the ability of this vaccine to induce long-term protection and is therefore an ideal candidate for a third generation vaccine against B. pertussis.

Increased susceptibility to pertussis in adults at childbearing age as determined by comparative seroprevalence study, China 2010-2016

OBJECTIVES

This study was aimed to determine pertussis specific serum PT-IgG antibodies in healthy individuals during 2010 and 2015/2016 in Beijing, China.

METHODS

A total of 3884 healthy individuals were included: 3058 aged 3-69 years randomly selected from an epidemiological survey conducted in 2010, and 826 aged 20-39 years selected from those who attended an annual medical examination in 2015/2016. Serum PT-IgG antibodies were determined using the Serion/Virion ELISA kits.

RESULTS

Of 3058 subjects in 2010, 167 (5.5%) and 39 (1.3%) subjects had PT-IgG antibodies ≥40 IU/ml and ≥100 IU/ml, respectively. No differences were observed among different age groups. Altogether, 26.2% had undetectable PT-IgG antibodies (<5 IU/ml), and the highest undetectable rate of 56.8% was found in children aged 3-5 years. When the age group of 20-39 years was compared between the two periods, no difference was found in seroprevalence of PT-IgG antibodies ≥ 40 IU/ml (5.1% vs. 4.0%). However, an undetectable rate of PT-IgG antibodies was significantly higher in 2015/2016 than that in 2010 (57.4% vs. 29.1%, p < 0.001).

CONCLUSIONS

Our results showed that about 5% of individuals had PT-IgG antibodies indicative of a recent infection, and adults at childbearing age have an increased risk to pertussis in China.

Genome Sequence of Bordetella pertussis Vaccine Strain BP 165

Whole-cell and acellular pertussis vaccines are used globally against Bordetella pertussis. Various vaccine reference strains are used globally for the production of such vaccines.

Whole-cell and acellular pertussis vaccines are used globally against Bordetella pertussis. Various vaccine reference strains are used globally for the production of such vaccines. We report here a draft genome sequence for Bordetella pertussis strain BP 165, which is used by the Serum Institute of India in the production of acellular pertussis vaccine.

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.

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.

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.

Bordetella pertussis isolates vary in their interactions with human complement components

Whooping cough is a re-emerging respiratory tract infection. It has become clear that there is a need for better understanding of protective immune responses and variation between Bordetella pertussis strains to aid the development of improved vaccines. In order to survive in the host, B. pertussis has evolved mechanisms to evade complement-mediated killing, including the ability to bind complement-regulatory proteins. Here we evaluate the variation in interactions with the complement system among recently isolated strains. Isolates whose genomes appear highly similar and cluster together on a SNP-based dendrogram were found to vary significantly in resistance to complement-mediated killing and in the deposition of C3b/iC3b, C5b-9 and C1 esterase inhibitor (C1-INH). The key role of Vag8 as a receptor for C1-INH was confirmed and its expression was shown to vary in a panel of isolates. A Vag8 knockout mutant showed increased sensitivity to complement-mediated killing. Antibodies in convalescent sera blocked C1-INH binding to B. pertussis and may play an important role in natural immunity.

Pertussis epidemiology in Argentina: TRENDS after the introduction of maternal immunisation

Data on the impact of the recently recommended maternal pertussis vaccination are promising, but still insufficient to universalise this approach. We thus compared the epidemiological data prior to the implementation of this vaccination strategy in Argentina (2012) with the figures reported after 2012. During that 2010–2016 period, two outbreaks occurred, one in 2011 and another in 2016. In the former, the incidence was 6.9/100 000 inhabitants and the case-fatality rate 2.6%. Thereafter, a decline in incidence was detected until 2014. During 2015 and 2016 an increase in the incidence transpired, but this rise was fortunately not accompanied by one in the case fatality ratio. Indeed, in 2016 the case fatality ratio was the lowest (0.6%). Moreover, during the 2016 outbreak, the incidence (3.9/100 000 inhabitants) and the case severity detected in the most vulnerable population (infants 0–2 months) were both lower than those in 2011. Consistent with this pattern, in 2016, in the most populated province of Argentina (Buenos Aires), the case percentage with laboratory-positive results indicating a high number of symptoms (59.1% of the total cases) diminished compared with that detected in the 2011 outbreak without maternal immunisation (71.9%). Using the mathematical model of pertussis transmission we previously designed, we assessed the effect of vaccination during pregnancy on infant incidence. From comparisons between the epidemiological data made through calculations, emerged the possibility that vaccinating women during pregnancy would benefit the infants beyond age 2 months, specifically in the 2–12-month cohort.

Species interactions may help explain the erratic periodicity of whooping cough dynamics

Incidence of whooping cough exhibits variable dynamics across time and space. The periodicity of this disease varies from annual to five years in different geographic regions in both developing and developed countries. Many hypotheses have been put forward to explain this variability such as nonlinearity and seasonality, stochasticity, variable recruitment of susceptible individuals via birth, immunization, and immune boosting. We propose an alternative hypothesis to describe the variability in periodicity - the intricate dynamical variability of whooping cough may arise from interactions between its dominant etiological agents of Bordetella pertussis and Bordetella parapertussis. We develop a two-species age-structured model, where two pathogens are allowed to interact by age-dependent convalescence of individuals with severe illness from infections. With moderate strength of interactions, the model exhibits multi-annual coexisting attractors that depend on the R₀ of the two pathogens. We also examine how perturbation from case importation and noise in transmission may push the system from one dynamical regime to another. The coexistence of multi-annual cycles and the behavior of switching between attractors suggest that variable dynamics of whopping cough could be an emergent property of its multi-agent etiology.

Pertussis Maternal Immunization: Narrowing the Knowledge Gaps on the Duration of Transferred Protective Immunity and on Vaccination Frequency

Maternal safety through pertussis vaccination and subsequent maternal–fetal-antibody transfer are well documented, but information on infant protection from pertussis by such antibodies and by subsequent vaccinations is scarce. Since mice are used extensively for maternal-vaccination studies, we adopted that model to narrow those gaps in our understanding of maternal pertussis immunization. Accordingly, we vaccinated female mice with commercial acellular pertussis (aP) vaccine and measured offspring protection against Bordetella pertussis challenge and specific-antibody levels with or without revaccination. Maternal immunization protected the offspring against pertussis, with that immune protection transferred to the offspring lasting for several weeks, as evidenced by a reduction (4–5 logs, p < 0.001) in the colony-forming-units recovered from the lungs of 16-week-old offspring. Moreover, maternal-vaccination-acquired immunity from the first pregnancy still conferred protection to offspring up to the fourth pregnancy. Under the conditions of our experimental protocol, protection to offspring from the aP-induced immunity is transferred both transplacentally and through breastfeeding. Adoptive-transfer experiments demonstrated that transferred antibodies were more responsible for the protection detected in offspring than transferred whole spleen cells. In contrast to reported findings, the protection transferred was not lost after the vaccination of infant mice with the same or other vaccine preparations, and conversely, the immunity transferred from mothers did not interfere with the protection conferred by infant vaccination with the same or different vaccines. These results indicated that aP-vaccine immunization of pregnant female mice conferred protective immunity that is transferred both transplacentally and via offspring breastfeeding without compromising the protection boostered by subsequent infant vaccination. These results—though admittedly not necessarily immediately extrapolatable to humans—nevertheless enabled us to test hypotheses under controlled conditions through detailed sampling and data collection. These findings will hopefully refine hypotheses that can then be validated in subsequent human studies.

Multi-locus variable-number tandem repeat analysis of Bordetella pertussis isolates circulating in Poland in the period 1959-2013

PURPOSE

Despite the long history of pertussis vaccination and high vaccination coverage in Poland and many other developed countries, pertussis incidence rates have increased substantially, making whooping cough one of the most prevalent vaccine-preventable diseases. Among the factors potentially involved in pertussis resurgence, the adaptation of the Bordetella pertussis population to country-specific vaccine-induced immunity through selection of non-vaccine-type strains still needs detailed studies.

METHODOLOGY

Multi-locus variable-number tandem repeat analysis (MLVA), also linked to MLST and PFGE profiling, was applied to trace the genetic changes in the B. pertussis population circulating in Poland in the period 1959-2013 versus country-specific vaccine strains.

RESULTS

Generally, among 174 B. pertussis isolates, 31 MLVA types were detected, of which 11 were not described previously. The predominant MLVA types of recent isolates in Poland were different from those of the typical isolates circulating in other European countries. The MT27 type, currently predominant in Europe, was rarely seen and detected in only five isolates among all studied. The features of the vaccine strains used for production of the pertussis component of a national whole-cell diphtheria-tetanus-pertussis (DTP) vaccine, as studied by MLVA and MLST tools, were found to not match those observed in the currently circulating B. pertussis isolates in Poland.

CONCLUSIONS

Differences traced by MLVA in relation to the MLST and PFGE profiling confirmed that the B. pertussis strain types currently observed elsewhere in Europe, even if appearing in Poland, were not able to successfully disseminate within a human population in Poland that has been vaccinated with a whole-cell pertussis vaccine not used in other countries.

Immunogenicity and protective efficacy of recombinant iron superoxide dismutase protein from Bordetella pertussis in mice models

Whooping cough (pertussis) is a highly contagious respiratory infection caused by Bordetella pertussis. Although availability of effective pertussis vaccines reportedly decreases the incidence of the disease, B. pertussis circulation in populations has not been eliminated. Thus, it is necessary to find new protein candidates with greater immune protective capacities than the currently available acellular pertussis vaccines. In this study, iron superoxide dismutase (FeSOD) gene (sodB) was cloned, expressed in Escherichia coli and recombinant FeSOD protein thence purified. The recombinant protein (rFeSOD) was formulated with aluminum hydroxide (Alum) or monophosphoryl lipid A (MPLA) and injected intraperitoneally to immunize mice, after which IgG1, IgG2a and IFN-γ titers were measured to assess humoral and cellular responses, respectively, to these immunizations. The extent of bacterial colonization in lungs of intranasally challenged mice was determined 5, 8 and 14 days post-challenge. IgG1 and IgG2a responses were significantly stronger in mice that had been immunized with rFeSOD-MPLA than in those that had received rFeSOD-Alum (P < 0.05). Additionally, IgG2a titers were higher in mice vaccinated with recombinant protein FeSOD (rFeSOD) formulated with MPLA, especially after the second immunization. Immunization with rFeSOD-MPLA also provided a modest, but significant decrease in bacterial counts in lungs of mice (P < 0.05). Antigen specific-IFN-γ responses were significantly stronger in the group vaccinated with rFeSOD-MPLA, which could account for the lower bacterial counts. These findings suggest that rFeSOD protein formulated with MPLA has potential as an acellular pertussis vaccine candidate component.

Is the current pertussis incidence only the results of testing? A spatial and space-time analysis of pertussis surveillance data using cluster detection methods and geographically weighted regression modelling

BACKGROUND

Despite high vaccination coverage, pertussis incidence in the Netherlands is amongst the highest in Europe with a shifting tendency towards adults and elderly. Early detection of outbreaks and preventive actions are necessary to prevent severe complications in infants. Efficient pertussis control requires additional background knowledge about the determinants of testing and possible determinants of the current pertussis incidence. Therefore, the aim of our study is to examine the possibility of locating possible pertussis outbreaks using space-time cluster detection and to examine the determinants of pertussis testing and incidence using geographically weighted regression models.

METHODS

We analysed laboratory registry data including all geocoded pertussis tests in the southern area of the Netherlands between 2007 and 2013. Socio-demographic and infrastructure-related population data were matched to the geo-coded laboratory data. The spatial scan statistic was applied to detect spatial and space-time clusters of testing, incidence and test-positivity. Geographically weighted Poisson regression (GWPR) models were then constructed to model the associations between the age-specific rates of testing and incidence and possible population-based determinants.

RESULTS

Space-time clusters for pertussis incidence overlapped with space-time clusters for testing, reflecting a strong relationship between testing and incidence, irrespective of the examined age group. Testing for pertussis itself was overall associated with lower socio-economic status, multi-person-households, proximity to primary school and availability of healthcare. The current incidence in contradiction is mainly determined by testing and is not associated with a lower socioeconomic status.

DISCUSSION

Testing for pertussis follows to an extent the general healthcare seeking behaviour for common respiratory infections, whereas the current pertussis incidence is largely the result of testing. More testing would thus not necessarily improve pertussis control. Detecting outbreaks using space-time cluster detection is feasible but needs to adjust for the strong impact of testing on the detection of pertussis cases.

Influence of maternal vaccination against diphtheria, tetanus, and pertussis on the avidity of infant antibody responses to a pertussis containing vaccine in Belgium

Maternal antibodies induced by vaccination during pregnancy cross the placental barrier and can close the susceptibility gap to pertussis in young infants up to the start of primary immunization. As not only the quantity but also the quality of circulating antibodies is important for protection, we assessed whether maternal immunization affects the avidity of infant vaccine-induced IgG antibodies, in the frame of a prospective clinical trial on pregnancy vaccination in Belgium. Infants born from Tdap (Boostrix®) vaccinated (N = 55) and unvaccinated (N = 26) mothers were immunized with a hexavalent pertussis containing vaccine (Infanrix Hexa®) at 8, 12 and 16 weeks, followed by a fourth dose at 15 months of age. Right before and one month after this fourth vaccine dose, the avidity of IgG antibodies against diphtheria toxin (DT), tetanus toxin (TT), pertussis toxin (PT), filamentous hemagglutinin (FHA) and pertactin (Prn) was determined using 1.5 M ammonium thiocyanate as dissociating agent. In both groups, antibody avidity was moderate for TT, PT, FHA and Prn and low for DT after priming. After a fourth dose, antibody avidity increased significantly to high avidity for TT and PT, whereas it remained moderate for FHA and Prn and low for DT. The avidity correlated positively with antibody level in both study groups, yet not significantly for PT. When comparing both study groups, only PT-specific antibodies showed significantly lower avidity in infants born from vaccinated than from unvaccinated mothers after the fourth vaccine dose. The clinical significance of lower avidity of vaccine induced infant antibodies after maternal vaccination, if any, needs further investigation.

The Burden of Pertussis Hospitalization in HIV-Exposed and HIV-Unexposed South African Infants

BACKGROUND

 There are limited data on pertussis in African children, including among human immunodeficiency virus (HIV)-exposed infants. We conducted population-based hospital surveillance to determine the incidence and clinical presentation of Bordetella pertussis-associated hospitalization in perinatal HIV-exposed and -unexposed infants.

METHODS

 Children <12 months of age hospitalized with any sign or symptom of respiratory illness (including suspected sepsis or apnea in neonates) were enrolled from 1 January 2015 to 31 December 2015. Detailed clinical and demographic information was recorded and respiratory samples were tested by polymerase chain reaction (PCR).

RESULTS

 The overall B. pertussis PCR positivity was 2.3% (42/1839), of which 86% (n = 36) occurred in infants <3 months of age. Bordetella pertussis was detected in 2.1% (n = 26/1257) of HIV-unexposed and 2.7% (n = 16/599) of HIV-exposed infants. The incidence (per 1000) of B. pertussis-associated hospitalization was 2.9 (95% confidence interval [CI], 1.8-4.5) and 1.9 (95% CI, 1.3-2.6) in HIV-exposed and HIV-unexposed infants, respectively (P = .09). The overall in-hospital case fatality ratio among the cases was 4.8% (2/42), both deaths of which occurred in HIV-exposed infants <3 months of age. Among cases, presence of cough ≥14 days (20.5%) and paroxysmal coughing spells (33.3%) at diagnosis were uncommon. Only 16 (38%) B. pertussis-associated hospitalizations fulfilled the Centers for Diseases Control and Prevention case definition of "definite" pertussis.

CONCLUSIONS

 Bordetella pertussis contributed to a modest proportion of all-cause respiratory illness hospitalization among black-African children, with a trend for higher incidence among HIV-exposed than HIV-unexposed infants. Maternal vaccination of pregnant women should be considered to reduce the burden of pertussis hospitalization in this population.

Better colonisation of newly emerged Bordetella pertussis in the co-infection mouse model study

Molecular epidemiological data indicates that the resurgence of pertussis (whooping cough) in populations with high vaccine coverage is associated with genomic adaptation of Bordetella pertussis, the causative agent of the disease, to vaccine selection pressure. We have previously shown that in the period after the introduction of acellular pertussis vaccine (ACV), the majority of circulating strains in Australia switched to single nucleotide polymorphism (SNP) cluster I (carrying ptxP3/prn2), replacing SNP cluster II (carrying ptxP1/prn3). In this study, we carried out an in vivo competition assay using a mouse model infected with SNP cluster I and II B. pertussis strains from Australia. We found that the SNP cluster I strain colonised better than the SNP cluster II strain, in both naïve and immunised mice, suggesting that SNP cluster I strains had better fitness regardless of immunisation status of the host, consistent with SNP cluster I strains replacing SNP cluster II. Nevertheless, we found that ACV enhanced clearance of both SNP cluster I and II strains from the mouse respiratory tract.

A Functional Tricarboxylic Acid Cycle Operates during Growth of Bordetella pertussis on Amino Acid Mixtures as Sole Carbon Substrates

It has been claimed that citrate synthase, aconitase and isocitrate dehydrogenase activities are non-functional in Bordetella pertussis and that this might explain why this bacterium’s growth is sometimes associated with accumulation of polyhydroxybutyrate (PHB) and/or free fatty acids. However, the sequenced genome includes the entire citric acid pathway genes. Furthermore, these genes were expressed and the corresponding enzyme activities detected at high levels for the pathway when grown on a defined medium imitating the amino acid content of complex media often used for growth of this pathogenic microorganism. In addition, no significant PHB or fatty acids could be detected. Analysis of the carbon balance and stoichiometric flux analysis based on specific rates of amino acid consumption, and estimated biomass requirements coherent with the observed growth rate, clearly indicate that a fully functional tricarboxylic acid cycle operates in contrast to previous reports.

Restricted antibody response to Bordetella pertussis filamentous hemagglutinin induced by whole-cell and acellular pertussis vaccines

BACKGROUND

Filamentous hemagglutinin (FHA) is a principal virulence factor, an important immunogenic antigen of Bordetella pertussis, and a major component of many acellular pertussis vaccines. In the present study, the human antibody response to different regions of FHA was determined in healthy children and adults vaccinated with either whole-cell or acellular pertussis vaccines.

METHODS

To define the immunodominant regions of FHA, four overlapping recombinant fragments were expressed and produced in Escherichia coli and then purified by His-tagged based affinity chromatography. Two groups comprising healthy preschool children (n = 50) and adults (n = 26) were vaccinated with a single dose of commercial whole-cell and acellular DTaP vaccines, respectively. An antigen-based ELISA was applied to measure serum levels of anti-FHA antibody to both native and recombinant proteins in vaccinated volunteers.

RESULTS

In both groups of vaccinated individuals, the anti-FHA antibody response was mainly directed against epitopes located within a fragment of FHA spanning amino acid residues 1877-2250 of the mature FHA molecule (p < 0.001). No or little antibody was detected against the other recombinant segments of FHA.

CONCLUSION

Our results suggest that the human antibody response to FHA is directed to an immunodominant region located within residues 1877-2250 of the FHA molecule. Characterization and epitope mapping of the major components of acellular pertussis vaccine and future modifications in vaccine formulation may improve its efficacy and protectivity.

Investigating pertussis toxin and its impact on vaccination

Whooping cough, caused by Bordetella pertussis, remains a major global health problem. Each year around 40 million of pertussis cases resulting in 200,000-400,000 annual deaths occur worldwide. Pertussis toxin is a major virulence factor of B. pertussis. Murine studies have shown its importance in bacterial colonization and in immunomodulation to evade innate or adaptive immunity. The toxin is composed of an A protomer expressing ADP-ribosyltransferase activity and a B oligomer, responsible for toxin binding to target cells. The toxin is also a major protective antigen in all currently available vaccines. However, vaccine escape mutants with altered toxin expression have recently been isolated in countries with high vaccination coverage illustrating the need for improved pertussis vaccines.

Genetic Variation of Bordetella pertussis in Austria

In Austria, vaccination coverage against Bordetella pertussis infections during infancy is estimated at around 90%. Within the last years, however, the number of pertussis cases has increased steadily, not only in children but also in adolescents and adults, indicating both insufficient herd immunity and vaccine coverage. Waning immunity in the host and/or adaptation of the bacterium to the immunised hosts could contribute to the observed re-emergence of pertussis. In this study we therefore addressed the genetic variability in B. pertussis strains from several Austrian cities. Between the years 2002 and 2008, 110 samples were collected from Vienna (n = 32), Linz (n = 63) and Graz (n = 15) by nasopharyngeal swabs. DNA was extracted from the swabs, and bacterial sequence polymorphisms were examined by MLVA (multiple-locus variable number of tandem repeat analysis) (n = 77), by PCR amplification and conventional Sanger sequencing of the polymorphic regions of the prn (pertactin) gene (n = 110), and by amplification refractory mutation system quantitative PCR (ARMS-qPCR) (n = 110) to directly address polymorphisms in the genes encoding two pertussis toxin subunits (ptxA and ptxB), a fimbrial adhesin (fimD), tracheal colonisation factor (tcfA), and the virulence sensor protein (bvgS). Finally, the ptxP promoter region was screened by ARMS-qPCR for the presence of the ptxP3 allele, which has been associated with elevated production of pertussis toxin. The MLVA analysis revealed the highest level of polymorphisms with an absence of MLVA Type 29, which is found outside Austria. Only Prn subtypes Prn1/7, Prn2 and Prn3 were found with a predominance of the non-vaccine type Prn2. The analysis of the ptxA, ptxB, fimD, tcfA and bvgS polymorphisms showed a genotype mixed between the vaccine strain Tohama I and a clinical isolate from 2006 (L517). The major part of the samples (93%) displayed the ptxP3 allele. The consequences for the vaccination strategy are discussed.

A Proteomic Characterization of Bordetella pertussis Clinical Isolates Associated with a California State Pertussis Outbreak

Bordetella pertussis (Bp) is the etiologic agent of pertussis (whooping cough), a highly communicable infection. Although pertussis is vaccine preventable, in recent years there has been increased incidence, despite high vaccine coverage. Possible reasons for the rise in cases include the following: Bp strain adaptation, waning vaccine immunity, increased surveillance, and improved clinical diagnostics. A pertussis outbreak impacted California (USA) in 2010; children and preadolescents were the most affected but the burden of disease fell mainly on infants. To identify protein biomarkers associated with this pertussis outbreak, we report a whole cellular protein characterization of six Bp isolates plus the pertussis acellular vaccine strain Bp Tohama I (T), utilizing gel-free proteomics-based mass spectrometry (MS). MS/MS tryptic peptide detection and protein database searching combined with western blot analysis revealed three Bp isolates in this study had markedly reduced detection of pertactin (Prn), a subunit of pertussis acellular vaccines. Additionally, antibody affinity capture technologies were implemented using anti-Bp T rabbit polyclonal antisera and whole cellular proteins to identify putative immunogens. Proteome profiling could shed light on pathogenesis and potentially lay the foundation for reduced infection transmission strategies and improved clinical diagnostics.

Assessment of antibody level and avidity against Bordetella pertussis in a cohort of Egyptian individuals aged 1-18 years

Pertussis specific antibodies were studied with respect to quality and quantity in a cohort of apparently healthy Egyptian children and adolescents, with their age range between 1 and 18 years, in an attempt to get a close and clear insight into the current humoral immunization status in this specified group and to try find a relation between the antibody levels and their avidities in eradication of this devastating infectious disease. Our results showed that avidity increase was most marked in young school children (6–8 years) where it seemed to reach a plateau in older children and adolescents. Antibody titer was highest in toddlers (1–2 years) and young school children (6–8 years) groups, most probably following vaccination and/or booster doses. Among children aged 1–5 years, 28% had highly avid and 50% had high titer antibodies, whereas in adolescents aged 13–18 years, 70% had highly avid antibodies and only 30% had high titer antibodies. The results clearly demonstrated that while levels of anti-Bordetella pertussis (B. pertussis) antibodies wane with growing age, the avidity seems to increase, to a plateau, irrespective of further antigen exposure in a pattern showing complete independence of avidity on concentration. The present study draws attention to the importance of avidity measurements, together with conventional ELISAs, for evaluating immunity against pertussis. Being based on a limited sample size, it could open doors for larger-scale surveys to be possible indicators for the need and timing of booster vaccination doses among Egyptians.

Complement evasion by Bordetella pertussis: implications for improving current vaccines

Bordetella pertussis causes whooping cough or pertussis, a highly contagious disease of the respiratory tract. Despite high vaccination coverage, reported cases of pertussis are rising worldwide and it has become clear that the current vaccines must be improved. In addition to the well-known protective role of antibodies and T cells during B. pertussis infection, innate immune responses such as the complement system play an essential role in B. pertussis killing. In order to evade this complement activation and colonize the human host, B. pertussis expresses several molecules that inhibit complement activation. Interestingly, one of the known complement evasion proteins, autotransporter Vag8, is highly expressed in the recently emerged B. pertussis isolates. Here, we describe the current knowledge on how B. pertussis evades complement-mediated killing. In addition, we compare this to complement evasion strategies used by other bacterial species. Finally, we discuss the consequences of complement evasion by B. pertussis on adaptive immunity and how identification of the bacterial molecules and the mechanisms involved in complement evasion might help improve pertussis vaccines.

Whole-cell pertussis vaccine potency assays: the Kendrick test and alternative assays

Whole-cell pertussis vaccines are still widely used across the globe and have been shown to produce longer lasting immunity against pertussis infection than acellular pertussis vaccines. Therefore, whole-cell vaccines are likely to continue to be used for the foreseeable future. The intracerebral mouse protection test (Kendrick test) is effective for determining the potency of whole-cell pertussis vaccines and is the only test that has shown a correlation with protection in children. Here we review the Kendrick test in terms of international requirements for vaccine potency and critical technical points to be considered for a successful test including test validity, in-house references and statistical analysis. There are objections to the Kendrick test on animal welfare and technical grounds. Respiratory challenge assays, nitric oxide induction assay and serological assays have been developed and have been proposed as possible methods which might provide alternatives to the Kendrick test. These methods and their limitations are also briefly discussed. Establishment of validated in vitro correlates of protection has yet to be achieved. New technical developments, such as genome sequence and the use of gene microarrays to screen responses triggered by vaccine components may also provide leads to alternative assays to the Kendrick test by identifying biomarkers of protection.

Predictors of Mortality in Mechanically Ventilated Critical Pertussis in a low Income Country

Background

Critical pertussis is characterized by severe respiratory failure, important leukocytosis, pulmonary hypertension, septic shock and encephalopathy.

Aim

To describe the clinical course of critical pertussis, and identify predictors of death at the time of presentation for medical care.

Methodology

Retrospective study conducted in children’s hospital Tunisian PICU between 01 January and 31 October 2013. Patients with critical pertussis confirmed by RT-PCR and requiring mechanical ventilation were included. Predictors of death were studied.

Results

A total of 17 patients was studied. Median age was 50 days. Mortality was 23%. Predictors risk of mortality were : high PRISM score (Pediatric Risk of Mortality Score) (p=0,007), shock (p=0,002), tachycardia (p=0,005), seizures (p=0,006), altered mental status (p=0,006), elevated WBC count (p=0,003) and hemodynamic support (p=0022). However, the difference did not reach statistical significance in comorbidity, pneumoniae, high pulmonary hypertension or exchange transfusion. Concomitant viral or bacterial co-infection was not related to poor outcome.

Conclusion

Young infants are at high risk to have critical pertussis. Despite advances in life support and the treatment of organ failure in childhood critical illness, critical pertussis remains difficult to treat.

Investigations into the emergence of pertactin-deficient Bordetella pertussis isolates in six European countries, 1996 to 2012

Pathogen adaptation has been proposed to contribute to the resurgence of pertussis. A striking recent example is the emergence of isolates deficient in the vaccine component pertactin (Prn). This study explores the emergence of such Prn-deficient isolates in six European countries. During 2007 to 2009, 0/83 isolates from the Netherlands, 0/18 from the United Kingdom, 0/17 Finland, 0/23 Denmark, 4/99 Sweden and 5/20 from Norway of the isolates collected were Prn-deficient. In the Netherlands and Sweden, respectively 4/146 and 1/8 were observed in a later period (2010–12). The Prn-deficient isolates were genetically diverse and different mutations were found to inactivate the prn gene. These are indications that Prn-deficiency is subject to positive selective pressure. We hypothesise that the switch from whole cell to acellular pertussis vaccines has affected the balance between ‘costs and benefits’ of Prn production by Bordetella pertussis to the extent that isolates that do not produce Prn are able to expand. The absence of Prn-deficient isolates in some countries may point to ways to prevent or delay the spread of Prn-deficient strains. In order to substantiate this hypothesis, trends in the European B. pertussis population should be monitored continuously.

Bordetella holmesii: an under-recognised Bordetella species

Bordetella holmesii, first described in 1995, is believed to cause both invasive infections (bacteraemia, meningitis, endocarditis, pericarditis, pneumonia, and arthritis) and pertussis-like symptoms. Infection with B holmesii is frequently misidentified as being with B pertussis, the cause of whooping cough, because routine diagnostic tests for pertussis are not species-specific. In this Review, we summarise knowledge about B holmesii diagnosis and treatment, and assess research needs. Although no fatal cases of B holmesii have been reported, associated invasive infections can cause substantial morbidities, even in previously healthy individuals. Antimicrobial treatment can be problematic because B holmesii's susceptibility to macrolides (used empirically to treat B pertussis) and third-generation cephalosporins (often used to treat invasive infections) is lower than would be expected. B holmesii's adaptation to human beings is continuing, and virulence might increase, causing the need for better diagnostic assays and epidemiological surveillance.

Bordetella pertussis proteins dominating the major histocompatibility complex class II-presented epitope repertoire in human monocyte-derived dendritic cells

Knowledge of naturally processed Bordetella pertussis-specific T cell epitopes may help to increase our understanding of the basis of cell-mediated immune mechanisms to control this reemerging pathogen. Here, we elucidate for the first time the dominant major histocompatibility complex (MHC) class II-presented B. pertussis CD4(+) T cell epitopes, expressed on human monocyte-derived dendritic cells (MDDC) after the processing of whole bacterial cells by use of a platform of immunoproteomics technology. Pertussis epitopes identified in the context of HLA-DR molecules were derived from two envelope proteins, i.e., putative periplasmic protein (PPP) and putative peptidoglycan-associated lipoprotein (PAL), and from two cytosolic proteins, i.e., 10-kDa chaperonin groES protein (groES) and adenylosuccinate synthetase (ASS). No epitopes were detectable from known virulence factors. CD4(+) T cell responsiveness in healthy adults against peptide pools representing epitope regions or full proteins confirmed the immunogenicity of PAL, PPP, groES, and ASS. Elevated lymphoproliferative activity to PPP, groES, and ASS in subjects within a year after the diagnosis of symptomatic pertussis suggested immunogenic exposure to these proteins during clinical infection. The PAL-, PPP-, groES-, and ASS-specific responses were associated with secretion of functional Th1 (tumor necrosis factor alpha [TNF-α] and gamma interferon [IFN-γ]) and Th2 (interleukin 5 [IL-5] and IL-13) cytokines. Relative paucity in the natural B. pertussis epitope display of MDDC, not dominated by epitopes from known protective antigens, can interfere with the effectiveness of immune recognition of B. pertussis. A more complete understanding of hallmarks in B. pertussis-specific immunity may advance the design of novel immunological assays and prevention strategies.

Antibody-mediated inhibition of Bordetella pertussis adenylate cyclase-haemolysin-induced macrophage cytotoxicity is influenced by variations in the bacterial population

Whooping cough is a vaccine-preventable disease presenting with epidemic cycles linked to natural and/or vaccine-driven evolution of the aetiological agent of the disease, Bordetella pertussis. Adenylate cyclase-haemolysin (AC-Hly) is a major toxin produced by this pathogen, which mediates macrophage apoptosis in vitro and in vivo. While current acellular pertussis vaccine (APV) formulations do not include AC-Hly, they all contain pertussis toxin and can comprise filamentous haemagglutinin (FHA), which interacts with AC-Hly, and pertactin (PRN), which has been hypothesized also to interact with AC-Hly. We aimed to study the capacity of specific antibodies to inhibit the in vitro B. pertussis AC-Hly-mediated cytotoxicity of J774A.1 murine macrophages in a background of a changing bacterial population. We demonstrate that: (i) clinical isolates of different types or PRN phenotype are all cytotoxic and lethal in the mouse model of respiratory infection; (ii) lack of PRN production does not impact AC-Hly-related phenotypes; (iii) anti-AC-Hly antibodies inhibit cell lysis whatever the phenotype of the isolate, while anti-PRN antibodies significantly inhibit cell lysis provided the isolate produces this antigen, which might be relevant in vivo for APV-induced immunity; and (iv) anti-FHA antibodies only inhibit lysis induced by isolates collected in 2012, maybe indicating specific characteristics of epidemic lineages of B. pertussis.

Lack of association between mannose binding lectin and antibody responses after acellular pertussis vaccinations

BACKGROUND

Mannose-binding lectin (MBL) is one of the key molecules in innate immunity and its role in human vaccine responses is poorly known. This study aimed to investigate the possible association of MBL polymorphisms with antibody production after primary and booster vaccinations with acellular pertussis vaccines in infants and adolescents.

METHODOLOGY/PRINCIPAL FINDINGS

Five hundred and sixty eight subjects were included in this study. In the adolescent cohort 355 subjects received a dose of diphtheria and tetanus toxoids and acellular pertussis (dTpa) vaccine ten years previously. Follow-up was performed at 3, 5 and 10 years. Infant cohort consisted of 213 subjects, who had received three primary doses of DTaP vaccine at 3, 5, and 12 months of age according to Finnish immunization program. Blood samples were collected before the vaccinations at 2,5 months of age and after the vaccinations at 13 months and 2 years of age. Concentrations of IgG antibodies to pertussis toxin, filamentous hemagglutinin, and pertactin and antibodies to diphtheria and tetanus toxoids were measured by standardized enzyme-linked immunosorbant assay. Single nucleotide polymorphisms of MBL2 gene exon1 (codons 52, 54, 57) were examined. MBL serum concentration was also measured from the adolescent cohort. No association was found with MBL2 exon 1 polymorphisms and antibody responses against vaccine antigens, after primary and booster dTpa vaccination.

CONCLUSIONS

This study indicates that MBL polymorphisms do not affect the production and persistence of antibodies after acellular pertussis vaccination. Our finding also suggests that MBL might not be involved in modulating antibody responses to the vaccines made of purified bacterial proteins.

Substantial gaps in knowledge of Bordetella pertussis antibody and T cell epitopes relevant for natural immunity and vaccine efficacy

The recent increase in whooping cough in vaccinated populations has been attributed to waning immunity associated with the acellular vaccine. The Immune Epitope Database (IEDB) is a repository of immune epitope data from the published literature and includes T cell and antibody epitopes for human pathogens. The IEDB conducted a review of the epitope literature, which revealed 300 Bordetella pertussis-related epitopes from 39 references. Epitope data are currently available for six virulence factors of B. pertussis: pertussis toxin, pertactin, fimbrial 2, fimbrial 3, adenylate cyclase and filamentous hemagglutinin. The majority of epitopes were defined for antibody reactivity; fewer T cell determinants were reported. Analysis of available protective correlates data revealed a number of candidate epitopes; however few are defined in humans and few have been shown to be protective. Moreover, there are a limited number of studies defining epitopes from natural infection versus whole cell or acellular/subunit vaccines. The relationship between epitope location and structural features, as well as antigenic drift (SNP analysis) was also investigated. We conclude that the cumulative data is yet insufficient to address many fundamental questions related to vaccine failure and this underscores the need for further investigation of B. pertussis immunity at the molecular level.