Rapid increase in pertactin-deficient Bordetella pertussis isolates, Australia

Roads to the development of improved pertussis vaccines paved by immunology

Current acellular pertussis vaccines have various shortcomings, which may contribute to their suboptimal efficacy and waning immunity in vaccinated populations. This calls for the development of new pertussis vaccines capable of inducing long-lived protective immunity. Immunization with whole cell pertussis vaccines and natural infection with Bordetella pertussis induce distinct and more protective immune responses when compared with immunization with acellular pertussis vaccines. Therefore, the immune responses induced with whole cell vaccine or after infection can be used as a benchmark for the development of third-generation vaccines against pertussis. Here, we review the literature on the immunology of B. pertussis infection and vaccination and discuss the lessons learned that will help in the design of improved pertussis vaccines.

To develop improved pertussis vaccines capable of inducing long-lived protective immunity, lessons have to be learned from immunology of Bordetella pertussis infection and current vaccination.

Pertussis in the Era of New Strains of Bordetella pertussis

Despite implementation of a successful vaccination program, pertussis remains a significant health problem. Although the incidence of pertussis in the United States is reduced by approximately 80% compared with incidence before the introduction of vaccination in the 1940s, deaths still occur and the unrecognized disease burden remains high, with 1 million Bordetella pertussis infections annually in the United States estimated by serologic surveys. Reasons for the resurgence and current prevalence of pertussis may be multifactorial and include waning vaccine-induced protection as well as lower vaccine effectiveness, failure to vaccinate, and changes in the organism itself.

Pertussis Across the Globe: Recent Epidemiologic Trends From 2000 to 2013

Pertussis has reemerged as a problem across the world. To better understand the nature of the resurgence, we reviewed recent epidemiologic data and we report disease trends from across the world. Published epidemiologic data from January 2000 to July 2013 were obtained via PubMed searches and open-access websites. Data on vaccine coverage and reported pertussis cases from 2000 through 2012 from the 6 World Health Organization regions were also reviewed. Findings are confounded not only by the lack of systematic and comparable observations in many areas of the world but also by the cyclic nature of pertussis with peaks occurring every 3-5 years. It appears that pertussis incidence has increased in school-age children in North America and western Europe, where acellular pertussis vaccines are used, but an increase has also occurred in some countries that use whole-cell vaccines. Worldwide, pertussis remains a serious health concern, especially for infants, who bear the greatest disease burden. Factors that may contribute to the resurgence include lack of booster immunizations, low vaccine coverage, improved diagnostic methods, and genetic changes in the organism. To better understand the epidemiology of pertussis and optimize disease control, it is important to improve surveillance worldwide, irrespective of pertussis vaccine types and schedules used in each country.

Risk factors for pertussis hospitalizations in Australians aged 45 years and over: A population based nested case-control study

Although studies have described factors associated with pertussis hospitalization in children, data on adult hospitalization are sparse. We examined the association between patient characteristics and hospitalization among older adults with pertussis. We conducted a nested case-control study of participants in the 45 and Up prospective cohort in New South Wales, Australia, with an incident pertussis diagnosis during 2006-2012. Cases were defined as those with a hospitalization coded as 'whooping cough' or 'non-specific respiratory disease/cough' between a week prior and 6 weeks after the diagnosis of pertussis based on laboratory tests. Controls were participants diagnosed with pertussis but not hospitalized. Among 265,287 participants, the incidence of pertussis and pertussis hospitalization was 83.9 (95% [confidence interval] CI, 78.7-89.6) and 2.9 (95% CI, 2.1-4.1)/100,000 person-years, respectively. Among 33 cases and 882 controls, factors associated with hospitalization were increasing age (compared to those 45-54 years, adjusted odds ratio [aOR] 5.4 (95% CI, 1.6-18.2) and 8.9 (95% CI, 2.3-34.7) in those aged 65-74 years and 75+ years, respectively) and smoking (ever versus never, aOR 2.37 (95% CI, 1.11-5.06)). The risk of pertussis hospitalization is substantially higher in ≥65 years old. A booster dose of diphtheria-tetanus-pertussis vaccine could be readily integrated into routine vaccination for this age group.

Bordetella pertussis evolution in the (functional) genomics era

The incidence of whooping cough caused by Bordetella pertussis in many developed countries has risen dramatically in recent years. This has been linked to the use of an acellular pertussis vaccine. In addition, it is thought that B. pertussis is adapting under acellular vaccine mediated immune selection pressure, towards vaccine escape. Genomics-based approaches have revolutionized the ability to resolve the fine structure of the global B. pertussis population and its evolution during the era of vaccination. Here, we discuss the current picture of B. pertussis evolution and diversity in the light of the current resurgence, highlight import questions raised by recent studies in this area and discuss the role that functional genomics can play in addressing current knowledge gaps.

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.

Strategies and new developments to control pertussis, an actual health problem

The aim of this article is to describe the current epidemiological situation of pertussis, as well as different short-term strategies that have been implemented to alleviate this threat. The state of the art of the development of new vaccines that are expected to provide long-lasting immunity against pertussis was also included.

Pertussis Resurgence Associated with Pertactin-Deficient and Genetically Divergent Bordetella Pertussis Isolates in Israel

The Bordetella pertussis polymerase chain reaction positivity rate changed after additional diphtheria-tetanus-acellular pertussis boosters in 2005 and 2008, 9.8%, 13.4%, 22% and 15.2% in 2010, 2011, 2012 and 2013, P < 0.001, respectively. New pulsed-field gel electrophoresis profiles were detected between 2009 and 2012. The proportion of pertactin-deficient isolates increased over time, 6.6% versus 7.1% versus 33.3% during 2005-2006, 2011-2012 and 2013-2014, P < 0.03, respectively.

Development of improved pertussis vaccine

Rates of infection with Bordetella pertussis, the gram-negative bacterium that causes the respiratory disease called whooping cough or pertussis, have not abated and 16 million cases with almost 200,000 deaths are estimated by the WHO to have occurred worldwide in 2008. Despite relatively high vaccination rates, the disease has come back in recent years to afflict people in numbers not seen since the pre-vaccine days. Indeed, pertussis is now recognized as a frequent infection not only in newborn and infants but also in adults. The disease symptoms also can be induced by the non-vaccine-preventable infection with the close species B. parapertussis for which an increasing number of cases have been reported. The epidemiologic situation and current knowledge of the limitations of pertussis vaccine point out the need to design improved vaccines. Several alternative approaches and their challenges are summarized.

Asymptomatic transmission and the resurgence of Bordetella pertussis

BACKGROUND

The recent increase in whooping cough incidence (primarily caused by Bordetella pertussis) presents a challenge to both public health practitioners and scientists trying to understand the mechanisms behind its resurgence. Three main hypotheses have been proposed to explain the resurgence: 1) waning of protective immunity from vaccination or natural infection over time, 2) evolution of B. pertussis to escape protective immunity, and 3) low vaccine coverage. Recent studies have suggested a fourth mechanism: asymptomatic transmission from individuals vaccinated with the currently used acellular B. pertussis vaccines.

METHODS

Using wavelet analyses of B. pertussis incidence in the United States (US) and United Kingdom (UK) and a phylodynamic analysis of 36 clinical B. pertussis isolates from the US, we find evidence in support of asymptomatic transmission of B. pertussis. Next, we examine the clinical, public health, and epidemiological consequences of asymptomatic B. pertussis transmission using a mathematical model.

RESULTS

We find that: 1) the timing of changes in age-specific attack rates observed in the US and UK are consistent with asymptomatic transmission; 2) the phylodynamic analysis of the US sequences indicates more genetic diversity in the overall bacterial population than would be suggested by the observed number of infections, a pattern expected with asymptomatic transmission; 3) asymptomatic infections can bias assessments of vaccine efficacy based on observations of B. pertussis-free weeks; 4) asymptomatic transmission can account for the observed increase in B. pertussis incidence; and 5) vaccinating individuals in close contact with infants too young to receive the vaccine ("cocooning" unvaccinated children) may be ineffective.

CONCLUSIONS

Although a clear role for the previously suggested mechanisms still exists, asymptomatic transmission is the most parsimonious explanation for many of the observations surrounding the resurgence of B. pertussis in the US and UK. These results have important implications for B. pertussis vaccination policy and present a complicated scenario for achieving herd immunity and B. pertussis eradication.

Predictors of disease severity in children hospitalized for pertussis during an epidemic

BACKGROUND

Australia recently experienced its worst pertussis epidemic since introduction of pertussis vaccine into the National Immunisation Program. This study aimed to determine factors associated with severe pertussis in hospitalized children during an epidemic using a novel pertussis severity scoring (PSS) system.

METHODS

This prospective, observational, multicenter study enrolled children hospitalized with laboratory confirmed pertussis from 8 tertiary pediatric hospitals during a 12 month period (May 2009-April 2010). Variables assessed included demographics, clinical symptoms and relevant medical and immunization history. Cases were scored using objective clinical findings with cases classified as either severe (PSS > 5) or not severe (PSS ≤ 5). Logistic regression models were used to predict variables associated with severe disease.

RESULTS

One hundred twenty hospitalized children 0-17 years of age were enrolled with a median PSS of 5 (interquartile range 3-7). Most (61.7%) were classified as not severe with 38.3% (46/120) severe. Most severe cases (54.3%) were <2 months of age. Presence of coinfection [odds ratio (OR): 4.82, CI: 1.66-14.00], <2 months old (OR: 4.76, CI: 1.48-15.32), fever >37.5°C (OR: 5.97, CI: 1.19-29.96) and history of prematurity (OR: 5.00, CI: 1.27-19.71) were independently associated with severe disease. A total of 70 cases in children ≥2 months of age, almost a third (n = 23) had not received pertussis vaccine.

CONCLUSIONS

Most severe pertussis occurred in young, unimmunized infants, although severe disease was also observed in children >12 months of age and previously vaccinated children. Children admitted with pertussis with evidence of coinfection, history of prematurity or fever on presentation need close monitoring.

Analysis of Bordetella pertussis clinical isolates circulating in European countries during the period 1998-2012

Despite more than 50 years of vaccination, pertussis is still an endemic disease, with regular epidemic outbreaks. With the exception of Poland, European countries have replaced whole-cell vaccines (WCVs) by acellular vaccines (ACVs) in the 1990s. Worldwide, antigenic divergence in vaccine antigens has been found between vaccine strains and circulating strains. In this work, 466 Bordetella pertussis isolates collected in the period 1998–2012 from 13 European countries were characterised by multi-locus antigen sequence typing (MAST) of the pertussis toxin promoter (ptxP) and of the genes coding for proteins used in the ACVs: pertussis toxin (Ptx), pertactin (Prn), type 2 fimbriae (Fim2) and type 3 fimbriae (Fim3). Isolates were further characterised by fimbrial serotyping, multi-locus variable-number tandem repeat analysis (MLVA) and pulsed-field gel electrophoresis (PFGE). The results showed a very similar B. pertussis population for 12 countries using ACVs, while Poland, which uses a WCV, was quite distinct, suggesting that ACVs and WCVs select for different B. pertussis populations. This study forms a baseline for future studies on the effect of vaccination programmes on B. pertussis populations.

Pertussis

Pertussis continues to be an important public-health issue. The high immunization coverage rates achieved, mainly in industrialized countries, have certainly decreased the spread of the pathogen. However, as immunity wanes, adolescents and adults play an important role in the dynamics of the infection. The surveillance system has several limitations and the underestimation of pertussis in adolescents, young adults and adults is mainly related to the atypical clinical characteristics of cases and the lack of lab confirmation. The real epidemiological impact of pertussis is not always perceived. The unavailability of comprehensive data should not hamper the adoption of active prophylactic measures designed to avoid the impact of waning immunity against pertussis. Different immunization strategies have been suggested and/or already adopted such as immunization of newborns, pre-school and school children, adolescents, adults, healthcare workers, childcare workers, pregnant women, cocoon strategy. Prevention of pertussis requires an integrated approach and the adoption of different immunization strategies, with the objective of achieving and maintaining high coverage rates.

Pertussis outbreak, southeastern Minnesota, 2012

OBJECTIVE

To describe clinical and laboratory findings from the 2012 southeastern Minnesota pertussis outbreak.

PATIENTS AND METHODS

Patients were selected for 2 parts of the study. In the first part, nasopharyngeal swabs from a convenience sample of 265 unique patients were used for both the clinician-requested polymerase chain reaction (PCR) test and culture. B pertussis isolates were tested for macrolide susceptibility and typed using whole genome sequencing and pulsed-field gel electrophoresis. Pertactin gene sequences were analyzed to identify pertactin-deficient B pertussis. In the second part, all patients seen at Mayo Clinic in Rochester, Minnesota, who had PCR results positive for Bordetella pertussis or Bordetella parapertussis between January 1, 2012, and December 31, 2012, were analyzed for patient demographic features and vaccination records.

RESULTS

One hundred sixty patients had results positive for B pertussis, and 21 patients had results positive for B parapertussis. Among the 265 swabs cultured, B pertussis was detected by both culture and PCR in 11. One swab was positive for B pertussis by culture alone, and 13 were positive by PCR alone. Polymerase chain reaction detected B pertussis more frequently than did culture (P=.001). No macrolide resistance was detected. All 12 isolates tested had an altered pertactin gene, including 9 with a signal sequence deletion, 2 with insertion sequence disruptions, and 1 with a premature stop codon. Nine and 3 isolates were pertactin types prn1 and prn2, respectively. Whole genome sequencing and pulsed-field gel electrophoresis detected the presence of multiple B pertussis strains. The mean age of patients with pertussis was younger than that of those without pertussis (15.6 and 25.5 years, respectively; P=.002). Compared with those whose test results were negative for B pertussis, fewer patients with positive results had received whole-cell pertussis vaccine (P=.02). In the subgroup who had received acellular vaccine exclusively, the time since the most recent pertussis vaccination in those with results positive for B pertussis was longer than that in those with negative results (1363 vs 1010 days; P=.004).

CONCLUSION

The 2012 pertussis outbreak in southeastern Minnesota included multiple strains of B pertussis, all putatively lacking pertactin. Our findings may indicate decreased efficacy of (and waning immunity from) acellular vaccines as contributors to the outbreak.

Pertussis: still a cause of death, seven decades into vaccination

PURPOSE OF REVIEW

We review the resurgence of pertussis, including recent trends in epidemiology and reasons for the resurgence, as well as updated vaccination schedules and recommendations.

RECENT FINDINGS

There has been a resurgence of pertussis in recent decades, in the United States and worldwide. This is a preventable cause of hospitalizations and deaths, especially among the infant population. Possible reasons for the resurgence include increased awareness via surveillance and reporting, diagnostic testing improvements, infant susceptibility coupled with exposure to infected caregivers, waning immunity despite complete vaccination, inferior long-term efficacy of acellular vaccines compared with whole-cell vaccines, circulating mutant strains of the bacterium, and parents refusing vaccination of their children. Progressively updated vaccine recommendations should be adhered to, as this is currently the only available tool to stem the public health challenge.

SUMMARY

The resurgence of pertussis is a multifaceted problem, but the implementation of immunization for all age groups is of utmost importance.

Pertactin-negative Bordetella pertussis strains in Canada: characterization of a dozen isolates based on a survey of 224 samples collected in different parts of the country over the last 20 years

OBJECTIVE

To detect and characterize pertactin-negative Bordetella pertussis in Canada, especially for isolates collected in recent years.

METHODS

A total of 224 isolates from the years 1994-2013 were screened by Western immuno-blot for expression of pertactin. Pertactin-negative isolates were characterized by serotyping, pulsed-field gel electrophoresis (PFGE), and genotyping of their pertactin, fimbriae 3, pertussis toxin subunit 1, and pertussis toxin gene promoter region, as well as the complete sequence of the pertactin gene.

RESULTS

Twelve isolates were pertactin-negative, giving an overall prevalence of 5.4%. However, no such isolate was found prior to 2011 and 17.8% of 62 isolates examined in 2012 were pertactin-negative. Ten pertactin-negative isolates contained a significant mutation in their pertactin (prn) genes. IS481 was found in the prn genes of eight isolates, while a single point mutation occurred either in the coding region (resulting in a premature stop codon) or in the promoter region (preventing gene transcription) in two other isolates. PFGE analysis also showed multiple profiles suggesting that several independent genetic events might have led to the emergence of these pertactin-negative strains rather than expansion of a single clone.

CONCLUSIONS

As reported elsewhere, pertactin-negative B. pertussis has emerged in Canada in recent years, notably in 2012. This coincided with an increase in pertussis activity in Canada. A further systematic study with a larger geographical representative sample is required to determine how these vaccine-negative strains may contribute to the overall changing epidemiology of pertussis in Canada.

Characterization of the key antigenic components of pertussis vaccine based on outer membrane vesicles

Pertussis has resurged during the last two decades in different countries. In particular in the 2010-2013 period large outbreaks were detected in US, Australia, UK and The Netherlands with significant mortality in infants. The epidemiological situation of pertussis points out the need to develop new vaccines and in this regard we previously developed a new vaccine based on outer membrane vesicles (OMVs) which have been shown to be safe and to induce protection in mice. Here we have further investigated the properties of OMVs vaccines; in particular we studied the contribution of pertussis toxin (PTx) and pertactin (Prn) in OMVs-mediated protection against pertussis. PTx-deficient OMVs and Prn-deficient OMVs were obtained from defective Bordetella pertussis mutants. The absence of PTx or Prn did compromise the protective capacity of the OMVs formulated as Tdap vaccine. Whereas the protective efficacy of the PTx-deficient OMVs in mice was comparable to Prn-deficient OMVs, the protective capacity of both of them was significantly impaired when it was compared with the wild type OMVs. Interestingly, using OMVs obtained from a B. pertussis strain which does not express any of the virulence factors but expresses the avirulent phenotype; we observed that the protective ability of such OMVs was lower than that of OMVs obtained from virulent B. pertussis phase. However, it was surprising that although the protective capacity of avirulent OMVs was lower, they were still protective in the used mice model. These results allow us to hypothesize that OMVs from avirulent phase shares protective components with all OMVs assayed. Using an immune proteomic strategy we identified some common components that could play an important role in protection against pertussis.

Proteomics-identified Bvg-activated autotransporters protect against bordetella pertussis in a mouse model

Pertussis is a highly infectious respiratory disease of humans caused by the bacterium Bordetella pertussis. Despite high vaccination coverage, pertussis has re-emerged globally. Causes for the re-emergence of pertussis include limited duration of protection conferred by acellular pertussis vaccines (aP) and pathogen adaptation. Pathogen adaptations involve antigenic divergence with vaccine strains, the emergence of strains which show enhanced in vitro expression of a number of virulence-associated genes and of strains that do not express pertactin, an important aP component. Clearly, the identification of more effective B. pertussis vaccine antigens is of utmost importance. To identify novel antigens, we used proteomics to identify B. pertussis proteins regulated by the master virulence regulatory system BvgAS in vitro. Five candidates proteins were selected and it was confirmed that they were also expressed in the lungs of naïve mice seven days after infection. The five proteins were expressed in recombinant form, adjuvanted with alum and used to immunize mice as stand-alone antigens. Subsequent respiratory challenge showed that immunization with the autotransporters Vag8 and SphB1 significantly reduced bacterial load in the lungs. Whilst these antigens induced strong opsonizing antibody responses, we found that none of the tested alum-adjuvanted vaccines - including a three-component aP - reduced bacterial load in the nasopharynx, suggesting that alternative immunological responses may be required for efficient bacterial clearance from the nasopharynx.

Molecular epidemiology of the pertussis epidemic in Washington State in 2012

Although pertussis disease is vaccine preventable, Washington State experienced a substantial rise in pertussis incidence beginning in 2011. By June 2012, the reported cases reached 2,520 (37.5 cases per 100,000 residents), a 1,300% increase compared with the same period in 2011. We assessed the molecular epidemiology of this statewide epidemic using 240 isolates collected from case patients reported from 19 of 39 Washington counties during 2012 to 2013. The typing methods included pulsed-field gel electrophoresis (PFGE), multilocus variable number tandem repeat analysis (MLVA), multilocus sequence typing (MLST), and pertactin gene (prn) mutational analysis. Using the scheme PFGE-MLVA-MLST-prn mutations-Prn deficiency, the 240 isolates comprised 65 distinct typing profiles. Thirty-one PFGE types were found, with the most common types, CDC013 (n = 51), CDC237 (n = 44), and CDC002 (n = 42), accounting for 57% of them. Eleven MLVA types were observed, mainly comprising type 27 (n = 183, 76%). Seven MLST types were identified, with the majority of the isolates typing as prn2-ptxP3-ptxA1-fim3-1 (n = 157, 65%). Four different prn mutations accounted for the 76% of isolates exhibiting pertactin deficiency. PFGE provided the highest discriminatory power (D = 0.87) and was found to be a more powerful typing method than MLVA and MLST combined (D = 0.67). This study provides evidence for the continued predominance of MLVA 27 and prn2-ptxP3-ptxA1 alleles, along with the reemergence of the fim3-1 allele. Our results indicate that the Bordetella pertussis population causing this epidemic was diverse, with a few molecular types predominating. The PFGE, MLVA, and MLST profiles were consistent with the predominate types circulating in the United States and other countries. For prn, several mutations were present in multiple molecular types.

A rapid ELISA-based method for screening Bordetella pertussis strain production of antigens included in current acellular pertussis vaccines

INTRODUCTION

Despite extensive vaccinations, there have been pertussis epidemics in many countries including the Netherlands, the UK, Australia and the USA. During these epidemics Bordetella pertussis strains not producing the vaccine antigen pertactin (Prn) are emerging and increasing in numbers. However, methods for confirming PRN production of B. pertussis isolates are combined PCR or PCR-based sequencing tests and western blotting. Furthermore, data about production of pertussis toxin (PT) and filamentous hemagglutinin (FHA) of these isolates are scarce. Fimbriae (Fim) production is usually determined by agglutination and reported as serotype. In this study we developed an easy, accurate and rapid method for screening PT and FHA production. Methods for Prn and Fim production have been published earlier.

METHODS

We analyzed altogether 109 B. pertussis strains, including 103 Finnish B. pertussis strains collected during 2006-2013, international strain Tohama I, French strains FR3496 (PT-negative), FR3693 (Prn-negative) and FR4624 (FHA-negative) and Fim-serotype reference strains S1 (producing only Fim2) and S3 (producing only Fim3). An indirect ELISA with whole bacterial cells as coating antigen was developed and used for rapid screening of the B. pertussis strains. Production of different antigens (PT, FHA, Prn, Fim2 and Fim3) was detected with specific monoclonal antibodies (mAbs).

RESULTS

From the 103 Finnish B. pertussis strains tested, all were positive for PT, FHA and Fim. Four were found negative for Prn, and they were isolated during 2011-2013.

CONCLUSIONS

The newly developed method proved to be useful and simple for rapid screening of different antigen production of B. pertussis isolates.

Acellular pertussis vaccines and pertussis resurgence: revise or replace?

The resurgence of pertussis (whooping cough) in countries with high vaccination coverage is alarming and invites reconsideration of the use of current acellular pertussis (aP) vaccines, which have largely replaced the old, reactogenic, whole-cell pertussis (wP) vaccine. Some drawbacks of these vaccines in terms of limited antigenic composition and early waning of antibody levels could be anticipated by the results of in-trial or postlicensure human investigations of B- and T-cell responses in aP versus wP vaccine recipients or unvaccinated, infected children. Recent data in experimental models, including primates, suggest that generation of vaccines capable of a potent, though regulated, stimulation of innate immunity driving effective, persistent adaptive immune responses against Bordetella pertussis infection should be privileged. Adjuvants that skew Th1/Th17 responses or new wP (detoxified or attenuated) vaccines should be explored. Nonetheless, the high merits of the current aP vaccines in persuading people to resume vaccination against pertussis should not be forgotten.