Clonal expansion of sequence type (ST-)5 and emergence of ST-7 in serogroup A meningococci, Africa

Long-term impacts of MenC vaccination campaign in the Salvador, Brazil metropolitan region: A comparison of pre- and post-vaccine periods

The Meningococcal Serogroup C Conjugate Vaccine (MenC) was introduced into the Brazilian Immunization Program in 2010. However, in Salvador, the fourth largest capital in Brazil, an extended catch-up campaign was conducted earlier in that year, which focused on adolescents and young adults aged 10-24 years. To evaluate the long-term impact of MenC vaccination, we analyzed hospital-based surveillance data on cases of meningococcal disease in the Salvador metropolitan region during the pre-vaccine (2005-2009) and post-vaccine (2011-2016) campaign periods. Six years after the introduction of the MenC vaccine, the mean incidence rate decreased from 3.20 to 0.93 cases per 100,000 individuals (71% reduction, 95% CI [58.7-83.3]) in children <4 years. Reductions of 25.6% and 21.1% were also observed for the age groups of 5-9 and 10-14 years, respectively. On the other hand, incidence increased in the 15-24-year age group from 0.72 to 1.11, and from 0.31 to 0.60 in individuals aged >25 years (p < 0.05). At the end of the study period, serogroup C was the most prevalent (65.7%), followed by serogroups B (9.8%), W (2.3%), Y (1.6%) and A (1.0%); serogrouping was not possible in 19.6% of the cases, or adequate material was not available for serogroup identification. The use of real-time PCR from 2010 onwards increased detection rates of meningococcal meningitis by 29.6%. The long-term impact of the MenC vaccination campaign was associated with a significant reduction in MenC disease in children aged 0-4 years, yet no effect was observed in adolescents and adults, as evidenced by increasing trends in infection rates. In addition, the emergence of meningococcal serogroup A was identified, which should serve as an alert to public health officials and deserves further investigation.

Invasive meningococcal disease in Shanghai, China from 1950 to 2016: implications for serogroup B vaccine implementation

Serogroup B invasive meningococcal disease (IMD) is increasing in China, but little is known about the causative meningococci. Here, IMD and carriage isolates in Shanghai characterised and the applicability of different vaccines assessed. Seven IMD epidemic periods have been observed in Shanghai since 1950, with 460 isolates collected including 169 from IMD and 291 from carriage. Analyses were divided according to the period of meningococcal polysaccharide vaccine (MPV) introduction: (i) pre-MPV-A, 1965–1980; (ii) post-MPV-A, 1981–2008; and (iii) post-MPV-A + C, 2009–2016. Over this period, IMD incidence decreased from 55.4/100,000 to 0.71 then to 0.02, corresponding to successive changes in meningococcal type from serogroup A ST-5 complex (MenA:cc5) to MenC:cc4821, and finally MenB:cc4821. MenB IMD became predominant (63.2%) in the post-MPV-A + C period, and 50% of cases were caused by cc4821, with the highest incidence in infants (0.45/100,000) and a case-fatality rate of 9.5%. IMD was positively correlated with population carriage rates. Using the Bexsero Antigen Sequence Type (BAST) system, fewer than 25% of MenB isolates in the post-MPV-A + C period contained exact or predicted cross reactive matches to the vaccines Bexsero, Trumenba, or an outer membrane vesicle (OMV)-based vaccine, NonaMen. A unique IMD epidemiology was seen in China, changing periodically from epidemic to hyperepidemic and low-level endemic disease. At the time of writing, MenB IMD dominated IMD in Shanghai, with isolates potentially beyond coverage with licenced OMV- and protein-based MenB vaccines.

Spontaneous point mutations in the capsule synthesis locus leading to structural and functional changes of the capsule in serogroup A meningococcal populations

Whole genome sequencing analysis of 100 Neisseria meningitidis serogroup A isolates has revealed that the csaABCD-ctrABCD-ctrEF capsule polysaccharide synthesis locus represents a spontaneous point mutation hotspot. Structural and functional properties of the capsule of 11 carriage and two disease isolates with non-synonymous point mutations or stop codons in capsule synthesis genes were analyzed for their capsular polysaccharide expression, recognition by antibodies and sensitivity to bactericidal killing. Eight of eleven carriage isolates presenting capsule locus mutations expressed no or reduced amounts of capsule. One isolate with a stop codon in the O-acetyltransferase gene expressed non-O-acetylated polysaccharide, and was not recognized by anti-capsule antibodies. Capsule and O-acetylation deficient mutants were resistant to complement deposition and killing mediated by anti-capsular antibodies, but not by anti-lipopolysaccharide antibodies. Two capsule polymerase mutants, one carriage and one case isolate, showed capsule over-expression and increased resistance against bactericidal activity of both capsule- and lipopolysaccharide-specific antibodies. Meningococci have developed multiple strategies for changing capsule expression and structure, which is relevant both for colonization and virulence. Here we show that point mutations in the capsule synthesis genes substantially contribute to the repertoire of genetic mechanisms in natural populations leading to variability in capsule expression.

Capsule switching of Neisseria meningitidis sequence type 7 serogroup A to serogroup X

OBJECTIVES

The bacterial pathogen Neisseria meningitidis is able to escape the currently available capsule-based vaccines by undergoing capsule switching. In this study, we investigated whether capsule switching has occurred in a recently emerged sequence type (ST) 7 serogroup X isolate in China, for which currently no vaccine is available.

METHODS

To identify capsule switching breakpoints, the capsule locus and flanking regions of the ST-7 serogroup X isolate and three endemic ST-7 serogroup A isolates were sequenced and compared. To obtain further insight into capsule switching frequency and length of DNA fragments involved, capsule switching assays were performed using genomic DNA containing combinations of antibiotic selection markers at various locations in the capsule locus and flanking regions.

RESULTS

Sequence analyses showed that capsule switching has occurred and involved a 8450 bp serogroup X DNA fragment spanning the region from galE to ctrC. Capsule switching assays indicate that capsule switching occurs at a frequency of 6.3 × 10^-6 per bacterium per μg of DNA and predominantly involved DNA fragments of about 8.1-9.6 kb in length.

CONCLUSIONS

Our results show that capsule switching in N. meningitidis occurs at high frequency and involves recombination in the flanking regions of the capsule biosynthesis genes.

Serogroup and Clonal Characterization of Czech Invasive Neisseria meningitidis Strains Isolated from 1971 to 2015

Background

This study presents antigenic and genetic characteristics of Neisseria meningitidis strains recovered from invasive meningococcal disease (IMD) in the Czech Republic in 1971–2015.

Material and Methods

A total of 1970 isolates from IMD, referred to the National Reference Laboratory for Meningococcal Infections in 1971–2015, were studied. All isolates were identified and characterized by conventional biochemical and serological tests. Most isolates (82.5%) were characterized by multilocus sequence typing method.

Results

In the study period 1971–2015, the leading serogroup was B (52.4%), most often assigned to clonal complexes cc32, cc41/44, cc18, and cc269. A significant percentage of strains were of serogroup C (41.4%), with high clonal homogeneity due to hyperinvasive complex cc11, which played an important role in IMD in the Czech Republic in the mid-1990s. Serogroup Y isolates, mostly assigned to cc23, and isolates of clonally homogeneous serogroup W have also been recovered more often over the last years.

Conclusion

The incidence of IMD and distribution of serogroups and clonal complexes of N. meningitidis in the Czech Republic varied over time, as can be seen from the long-term monitoring, including molecular surveillance data. Data from the conventional and molecular IMD surveillance are helpful in refining the antimeningococcal vaccination strategy in the Czech Republic.

The Global Evolution of Meningococcal Epidemiology Following the Introduction of Meningococcal Vaccines

Invasive meningococcal disease (IMD) caused by Neisseria meningitidis is associated with high morbidity and mortality. Although IMD incidence is highest in infants, a second peak occurs in adolescents/young adults. The incidence of IMD and the predominant disease-causing meningococcal serogroups vary worldwide. Epidemiologic data have guided the development of meningococcal vaccines to reduce the IMD burden. In Europe, serogroup C IMD has been substantially reduced since the introduction of a serogroup C conjugate vaccine. Serogroup B predominates in Europe, although cases of serogroup Y IMD have been increasing in recent years. In the United States, declines in serogroup C and Y disease have been observed in association with the introduction of quadrivalent (serogroups ACWY) meningococcal conjugate vaccines; serogroup B persists and is now the most common cause of outbreak associated disease. In the African meningitis belt, a conjugate vaccine for serogroup A has been effective in decreasing meningitis associated with that serogroup. Outbreaks of the previously rare serogroup X disease have been reported in this region since 2006. In recent years, outbreaks of serogroup B IMD, for which vaccines have only recently been approved by the U.S. Food and Drug Administration and the European Medicines Agency, have occurred in Europe and the United States. Targeting meningococcal vaccination to adolescents/young adults may reduce the morbidity and mortality associated with IMD and has the potential to impact the larger community through herd benefits.

Glycoconjugate vaccines: an update

INTRODUCTION

Globally, the three main pathogens causing serious infections are Haemophilus influenzae type b, Streptococcus pneumoniae and Neisseria meningitidis. Over the last 5 years, new vaccines protecting against these bacteria have been developed and introduced in various countries.

AREAS COVERED

This review describes the recently licensed glycoconjugates being used to protect against these encapsulated bacteria. Immunogenicity and safety data that led to licensure or licensure expansion of these glycoconjugates are discussed in addition to the resultant impact on the disease burden.

EXPERT OPINION

The maintenance of robust immunisation programmes with high uptake rates is important in maintaining low rates of disease. Epidemiological surveillance systems are essential in monitoring any changes in infectious disease trends and in identifying emerging infections such as from non-typeable H. influenzae, pneumococcal serotype replacement disease and changes in the epidemiology of meningococcal serogroups. This is important to guide future vaccine development. Accessibility of these glycoconjugate vaccines in resource poor regions, which bear the highest disease burden from these pathogens, remains challenging largely due to high vaccine pricing. Recent aids from public and private funding, tiered vaccine pricing and the transfer of vaccine technology have helped in introducing these vaccines where they are most needed.

Emergence of a new epidemic Neisseria meningitidis serogroup A Clone in the African meningitis belt: high-resolution picture of genomic changes that mediate immune evasion

In the African “meningitis belt,” outbreaks of meningococcal meningitis occur in cycles, representing a model for the role of host-pathogen interactions in epidemic processes. The periodicity of the epidemics is not well understood, nor is it currently possible to predict them. In our longitudinal colonization and disease surveys, we have observed waves of clonal replacement with the same serogroup, suggesting that immunity to noncapsular antigens plays a significant role in natural herd immunity. Here, through comparative genomic analysis of 100 meningococcal isolates, we provide a high-resolution view of the evolutionary changes that occurred during clonal replacement of a hypervirulent meningococcal clone (ST-7) by a descendant clone (ST-2859). We show that the majority of genetic changes are due to homologous recombination of laterally acquired DNA, with more than 20% of these events involving acquisition of DNA from other species. Signals of adaptation to evade herd immunity were indicated by genomic hot spots of recombination. Most striking is the high frequency of changes involving the pgl locus, which determines the glycosylation patterns of major protein antigens. High-frequency changes were also observed for genes involved in the regulation of pilus expression and the synthesis of Maf3 adhesins, highlighting the importance of these surface features in host-pathogen interaction and immune evasion.

While established meningococcal capsule polysaccharide vaccines are protective through the induction of anticapsular antibodies, findings of our longitudinal studies in the African meningitis belt have indicated that immunity to noncapsular antigens plays a significant role in natural herd immunity. Our results show that meningococci evade herd immunity through the rapid homologous replacement of just a few key genomic loci that affect noncapsular cell surface components. Identification of recombination hot spots thus represents an eminent approach to gain insight into targets of protective natural immune responses. Moreover, our results highlight the role of the dynamics of the protein glycosylation repertoire in immune evasion by Neisseria meningitidis. These results have major implications for the design of next-generation protein-based subunit vaccines.

Complete Genome Sequence of Neisseria meningitidis Serogroup A Strain NMA510612, Isolated from a Patient with Bacterial Meningitis in China

Serogroup A meningococcal strains have been involved in several pandemics and a series of epidemics worldwide in the past. Determination of the genome sequence of the prevalent genotype strain will help us understand the genetic background of the evolutionary and epidemiological properties of these bacteria. We sequenced the complete genome of Neisseria meningitidis NMA510612, a clinical isolate from a patient with meningococcal meningitis.

Sequence, distribution and chromosomal context of class I and class II pilin genes of Neisseria meningitidis identified in whole genome sequences

Background

Neisseria meningitidis expresses type four pili (Tfp) which are important for colonisation and virulence. Tfp have been considered as one of the most variable structures on the bacterial surface due to high frequency gene conversion, resulting in amino acid sequence variation of the major pilin subunit (PilE). Meningococci express either a class I or a class II pilE gene and recent work has indicated that class II pilins do not undergo antigenic variation, as class II pilE genes encode conserved pilin subunits. The purpose of this work was to use whole genome sequences to further investigate the frequency and variability of the class II pilE genes in meningococcal isolate collections.

Results

We analysed over 600 publically available whole genome sequences of N. meningitidis isolates to determine the sequence and genomic organization of pilE. We confirmed that meningococcal strains belonging to a limited number of clonal complexes (ccs, namely cc1, cc5, cc8, cc11 and cc174) harbour a class II pilE gene which is conserved in terms of sequence and chromosomal context. We also identified pilS cassettes in all isolates with class II pilE, however, our analysis indicates that these do not serve as donor sequences for pilE/pilS recombination. Furthermore, our work reveals that the class II pilE locus lacks the DNA sequence motifs that enable (G4) or enhance (Sma/Cla repeat) pilin antigenic variation. Finally, through analysis of pilin genes in commensal Neisseria species we found that meningococcal class II pilE genes are closely related to pilE from Neisseria lactamica and Neisseria polysaccharea, suggesting horizontal transfer among these species.

Conclusions

Class II pilins can be defined by their amino acid sequence and genomic context and are present in meningococcal isolates which have persisted and spread globally. The absence of G4 and Sma/Cla sequences adjacent to the class II pilE genes is consistent with the lack of pilin subunit variation in these isolates, although horizontal transfer may generate class II pilin diversity. This study supports the suggestion that high frequency antigenic variation of pilin is not universal in pathogenic Neisseria.

Epidemiological changes in meningococcal meningitis in Niger from 2008 to 2011 and the impact of vaccination

Background

The epidemiology of bacterial meningitis in the African ‘meningitis belt’ changes periodically. In order to design an effective vaccination strategy, we have examined the epidemiological and microbiological patterns of bacterial meningitis, and especially that of meningococcal meningitis, in Niger during the period 2008–2011. During this period a mass vaccination campaign with the newly developed meningococcal A conjugate vaccine (MenAfriVac®) was undertaken.

Method

Cerebrospinal fluid samples were collected from health facilities throughout Niger and analysed by culture, seroagglutination and/or speciation polymerase chain reaction, followed by genogrouping PCR for Neisseria meningitidis infections. A sample of strains were analysed by multi-locus sequence typing.

Results

N. meningitidis serogroup A cases were prevalent in 2008 and 2009 [98.6% and 97.5% of all N. meningitidis cases respectively]. The prevalence of serogroup A declined in 2010 [26.4%], with the emergence of serogroup W Sequence Type (ST) 11 [72.2% of cases], and the serogroup A meningococcus finally disappeared in 2011. The geographical distribution of cases N. meningitidis serogroups A and W within Niger is described.

Conclusion

The substantial decline of serogroup A cases that has been observed from 2010 onwards in Niger seems to be due to several factors including a major polysaccharide A/C vaccination campaign in 2009, the introduction of MenAfriVac® in 10 districts at risk in December 2010, the natural dynamics of meningococcal infection and the persistence of serogroup A sequence-type 7 for about 10 years. The emergence of serogroup W strains suggests that there may be a need for serogroup W containing vaccines in Niger in the coming years.

Phenotypic and genotypic characterization of meningococcal carriage and disease isolates in Burkina Faso after mass vaccination with a serogroup a conjugate vaccine

Background

The conjugate vaccine against serogroup A Neisseria meningitidis (NmA), MenAfriVac, was first introduced in mass vaccination campaigns of the 1-29-year-olds in Burkina Faso in 2010. The aim of this study was to genetically characterize meningococcal isolates circulating in Burkina Faso before and up to 13 months after MenAfriVac mass vaccination.

Methods

A total of 1,659 meningococcal carriage isolates were collected in a repeated cross-sectional carriage study of the 1-29-year-olds in three districts of Burkina Faso in 2010 and 2011, before and up to 13 months after mass vaccination. Forty-two invasive isolates were collected through the national surveillance in Burkina Faso in the same period. All the invasive isolates and 817 carriage isolates were characterized by serogroup, multilocus sequence typing and porA-fetA sequencing.

Results

Seven serogroup A isolates were identified, six in 2010, before vaccination (4 from carriers and 2 from patients), and one in 2011 from an unvaccinated patient; all were assigned to sequence type (ST)-2859 of the ST-5 clonal complex. No NmA carriage isolate and no ST-2859 isolate with another capsule were identified after vaccination. Serogroup X carriage and disease prevalence increased before vaccine introduction, due to the expansion of ST-181, which comprised 48.5% of all the characterized carriage isolates. The hypervirulent serogroup W ST-11 clone that was responsible for most of meningococcal disease in 2011 and 2012 was not observed in 2010; it appeared during the epidemic season of 2011, when it represented 40.6% of the serogroup W carriage isolates.

Conclusions

Successive clonal waves of ST-181 and ST-11 may explain the changing epidemiology in Burkina Faso after the virtual disappearance of NmA disease and carriage. No ST-2859 strain of any serogroup was found after vaccination, suggesting that capsule switching of ST-2859 did not occur, at least not during the first 13 months after vaccination.

Meningococcal disease in the Middle East and North Africa: an important public health consideration that requires further attention

This paper reviews the epidemiological data describing meningococcal disease in the Middle East and North Africa (MENA). While meningococcal disease remains an important cause of endemic and epidemic disease in many MENA countries, existing published epidemiological data appear limited, fragmented, and collected via disparate methodologies. Children aged 5 years and younger are predominantly affected, though outbreaks of the disease often affect older age groups. Whilst serogroup A remains a main cause of meningococcal disease in the region, cases of serogroup B, W-135, and Y have been increasingly reported over the last two decades in some countries. The Hajj pilgrimage is a key factor influencing outbreaks and transmission, and the use of vaccines has minimized the effects on the home countries of the pilgrims and has decreased global dissemination of disease. Wider use of available polyvalent meningococcal conjugate vaccines may provide broader protection against the range of serogroups causing disease or posing a threat in the region. In addition, strengthening regional surveillance systems and regularly publishing reports with reliable estimates of disease incidence, carriage, disease-related mortality, and sequelae may facilitate the development of appropriate interventions and public health strategies regarding meningococcal disease within the region.

Distribution of serogroups and sequence types in disease-associated and carrier strains of Neisseria meningitidis isolated in China between 2003 and 2008

Given the unpredictability of Neisseria meningitidis outbreaks and the increased prevalence of serogroup C strains following the introduction of serogroup A-based vaccines, we conducted an analysis of serogroups and sequence types (STs) in disease-associated and carrier N. meningitidis isolates that have emerged in China since 2003. We used multilocus sequence-typing techniques to investigate 371 N. meningitidis strains isolated from patients with meningitis and healthy carriers. Two lineages were identified in serogroup A and C isolates, genotyped as the ST5 complex and ST4821 complex, respectively. Both clonal complexes were found throughout China, although ST4821 was more concentrated in the eastern region of the country. The ST5 complex has been persistent in China since the late 1980s and has since spread across the entire country. Isolates belonging to the ST4821 complex have been a dominant lineage since 2003.

Microbiological and epidemiological investigation of the Neisseria meningitidis serogroup A epidemic in Niger in 2009: last wave before the introduction of the serogroup A meningococcal conjugate vaccine?

The 2009 meningitis season in Niger was characterized by an early onset, beginning in the very first weeks of the year and peaking from the 12th to the 15th week with 5655 clinical cases over the 4 weeks. From 1 January 2009 to 28 June 2009 (week 26), a total of 13,733 clinical cases of meningitis were reported to the national epidemiological surveillance system with a case-fatality rate of 4·2%. During the season 25 of the 42 health districts reached the epidemic threshold and 11 the alert threshold. Reactive mass vaccination campaigns involving a total of 5 166,741 doses of the polysaccharide meningococcal bivalent (A+C) vaccine progressively controlled the outbreak in most parts of the country. A total of 3755 cerebrospinal fluid samples representing 28·1% of the suspected meningitis cases were analysed. Serogroup A meningococci were the causative agent in 97·5% of the meningococcal cases. Multi-locus sequence typing of 26 meningococal serogroup A strains showed 25 sequence type (ST)7 and one ST2859, both sequence types belonging to the ST5 clonal complex (CC5) of subgroup III. This is the largest epidemic observed in Niger since those of 1995-1996 (59,948 notified cases) and 2000 (14,633 notified cases).

Modeling the cost-effectiveness of the integrated disease surveillance and response (IDSR) system: meningitis in Burkina Faso

Background

Effective surveillance for infectious diseases is an essential component of public health. There are few studies estimating the cost-effectiveness of starting or improving disease surveillance. We present a cost-effectiveness analysis the Integrated Disease Surveillance and Response (IDSR) strategy in Africa.

Methodology/Principal Findings

To assess the impact of the IDSR in Africa, we used pre- and post- IDSR meningococcal meningitis surveillance data from Burkina Faso (1996–2002 and 2003–2007). IDSR implementation was correlated with a median reduction of 2 weeks to peak of outbreaks (25^th percentile 1 week; 75^th percentile 4 weeks). IDSR was also correlated with a reduction of 43 meningitis cases per 100,000 (25^th–40: 75^th-129). Assuming the correlations between reductions in time to peak of outbreaks and cases are related, the cost-effectiveness of IDSR was $23 per case averted (25^th-$30; 75^th - cost saving), and $98 per meningitis-related death averted (25^th-$140: 75^th – cost saving).

Conclusions/Significance

We cannot absolutely claim that the measured differences were due to IDSR. We believe, however, that it is reasonable to claim that IDSR can improve the cost-effectiveness of public health surveillance.

Distribution of surface-protein variants of hyperinvasive meningococci in China

OBJECTIVE

Information regarding the different types of FetA and PorB meningococci that circulate in various regions of the world is still scarce. The present study investigated the distribution of FetA and PorB variable region (VR) types among meningococci belonging to hyperinvasive lineages circulating in China.

METHODS

The approach consisted of genotypic analysis of 201 Neisseria meningitidis strains belonging to hyperinvasive lineages isolated in China during the period 1956-2006.

RESULTS

Sixteen different PorB types were found, 8 of which were newly identified. Of the 24 different FetA VR types, 3 were determined to be novel. Particular combinations of FetA and PorB types associated with distinct clonal complexes were also observed. Most cases of invasive disease were caused by five individual clones: A: P1.7-1,10: F5-5: ST-3 (cc1) with P3.6,11,10,7 (class 3 PorB protein; VR1-6, VR2-11, VR3-10, and VR4-7); A: P1.20,9: F3-1: ST-5 (cc5) with P3.4,11,10,7; A: P1.20,9: F3-1: ST-5 (cc5) with P3.9,11,10,7; A: P1.20,9: F3-1: ST-7 (cc5) with P3.4,11,10,7; and C: P1.7-2,14: F3-3: ST-4821 (cc4821) with P3.9,15,6,7.

CONCLUSION

A number of antigen-gene variants and combinations exhibited broad temporal and geographic distributions, although several invasive clones were mainly associated with a specified timeframe. The changes that are increasingly emerging in circulating strains and the prevalent clone replacement describe the molecular epidemiology of meningococcal disease in China. Our findings have implications for both public-health monitoring and further study of this organism.

Characterization of serogroup A Neisseria meningitidis from invasive meningococcal disease cases in Canada between 1979 and 2006: Epidemiological links to returning travellers

INTRODUCTION

Serogroup A Neisseria meningitidis has repeatedly caused epidemics of invasive meningococcal disease (IMD) in developing nations since the 1960s. The present study is the first detailed study of serogroup A bacteria isolated in Canada.

METHODS

Thirty-four serogroup A meningococcal isolates collected from individuals with IMD in Canada between 1979 and 2006 were characterized by serology and multilocus sequence typing of seven housekeeping enzyme genes and genes encoding three outer membrane protein antigens.

RESULTS

Isolates were assigned to either the sequence type (ST)-1 or the ST-5 clonal complex. Clones within the ST-1 complex were recovered between 1979 and 1992, while clones of the ST-5 complex were isolated between 1987 and 2006; respectively, they accounted for 70.6% and 29.4% of all isolates studied. Isolates of the ST-1 complex were characterized by serosubtype antigen P1.3 or P1.3,6 with PorB allele 60 (serotype 4) and FetA sequence F5-1, while isolates of the ST-5 complex were characterized by serosubtype antigen P1.9 with PorB allele 47 (also serotype 4) and FetA sequence F3-1.

CONCLUSIONS

The Canadian serogroup A IMD isolates likely originated in travellers returning from hyperendemic or epidemic areas of the globe where serogroup A bacteria circulate. Although the Canadian cases of serogroup A IMD were caused by clones known to have caused epidemics in developing countries, disease incidence remained low in Canada.

ST2859 serogroup A meningococcal meningitis outbreak in Nouna Health District, Burkina Faso: a prospective study

We analysed cerebrospinal fluid samples from suspected meningitis cases in Nouna Health District, Burkina Faso, during the meningitis seasons of 2004-2006. Serogroup A ST2859 meningococci belonging to the ST5 clonal complex of subgroup III meningococci were the predominant causative agent. ST2859 bacteria were associated with focal outbreaks in the north of the district. While >10% of the population of an outbreak village carried ST2859, the population in the south of the district was predominantly colonised by serogroup Y ST4375 meningococci, which were associated with only sporadic cases of meningitis. Colonisation with the less virulent Y meningococci may interfere with the spread of the ST2859 to the south of the district, but there are concerns that this serogroup A clone may cause a third wave of subgroup III meningococcal disease in the African Meningitis Belt.

Genetic diversification of Neisseria meningitidis during waves of colonization and disease in the meningitis belt of sub-Saharan Africa

Although Neisseria meningitidis is a highly variable organism, most invasive disease is caused by a minority of genotypes. Hypervirulent lineages have been identified and their pandemic spread has been traced. During a longitudinal meningococcal colonization study in a district of northern Ghana clonal waves of carriage and disease were observed. Genetic diversification of genoclouds was analysed by pulsed field gel electrophoretic (PFGE) analysis of isolates from healthy carriers and from meningitis patients. Even during the limited time of persistence in the district, microevolution of the dominating genoclouds took place. Population genomic analyses are required to understand the genetic basis for the emergence of new lineages with epidemic potential, which is of crucial importance for the development of long-term global vaccination strategies against meningococcal disease.

Biological diagnosis of meningococcal meningitis in the African meningitis belt: Current epidemic strategy and new perspectives

Laboratory diagnosis is an essential component in surveillance of meningococcal epidemics, as it can inform decision-makers of the Neisseria meningitidis serogroup(s) involved and the most appropriate vaccine to be selected for mass vaccination. However, countries most affected face real limitations in laboratory diagnostics, due to lack of resources. We describe current diagnostic tools and examine their cost-effectiveness for use in an epidemic context. The conclusion is that current WHO recommendations to use only the latex agglutination assay (Pastorex) at epidemic onset is cost-effective, but recently developed rapid diagnostic tests for the major epidemic-causing meningococcal serogroups may prove a breakthrough for the future.

Meningococcal disease in South Africa, 1999-2002

Serogroups and strains differ by location, although hypervirulent strains were identified throughout the country.

We describe the epidemiology of invasive meningococcal disease in South Africa from August 1999 through July 2002, as reported to a laboratory-based surveillance system. Neisseria meningitidis isolates were further characterized. In total, 854 cases of laboratory-confirmed disease were reported, with an annual incidence rate of 0.64/100,000 population. Incidence was highest in infants <1 year of age. Serogroup B caused 41% of cases; serogroup A, 23%; serogroup Y, 21%; serogroup C, 8%; and serogroup W135, 5%. Serogroup B was the predominant serogroup in Western Cape Province, and disease rates remained stable. Serogroup A was most prevalent in Gauteng Province and increased over the 3 years. On pulsed-field gel electrophoresis analysis, serogroup A strains showed clonality, and serogroup B demonstrated considerable diversity. Selected isolates of serogroup A belonged to sequence type (ST)-1 (subgroup I/II) complex, serogroup B to ST-32/electrophoretic type (ET)-5 complex, and serogroup W135 to ST-11/ET-37 complex.

Meningitis epidemics in Africa: a brief overview

Every year, meningococcal meningitis causes thousands of deaths within the meningitis belt in sub-Saharan African countries. Large epidemic waves occur with a periodicity of 5-12 years. The waves do correspond to molecular changes in the expression of capsular or subcapsular antigens, which allow the bug to spread in susceptible populations. Serogroup A remains the major killer, even if in 2002, serogroup W135 ST-11 emerged in Burkina Faso, causing an important epidemic. However, the surveillance in the following years has showed a decrease in the W135 incidence and a clear predominance of serogroup A. Moreover, a new serogroup A strain belonging to ST-2859 seems to emerge and does represent a new threat for the coming seasons. In a vaccine perspective, and especially in the context of the development of an A conjugate vaccine; it is the key to strengthen the surveillance systems and to include molecular epidemiology as a tool for monitoring the molecular evolution of Neisseria meningitidis in Africa.

Serum antibody responses in Ethiopian meningitis patients infected with Neisseria meningitidis serogroup A sequence type 7

To elucidate critical components of protective immune responses induced during the natural course of serogroup A meningococcal disease, we studied acute-, early-convalescent-, and late-convalescent-phase sera from Ethiopian patients during outbreaks in 2002 to 2003. Sera were obtained from laboratory-confirmed patients positive for serogroup A sequence type 7 (ST-7) meningococci (A:4/21:P1.20,9) (n = 71) and from Ethiopian controls (n = 113). The sera were analyzed using an enzyme-linked immunosorbent assay to measure levels of immunoglobulin G (IgG) against serogroup A polysaccharide (APS) and outer membrane vesicles (OMVs) and for serum bactericidal activity (SBA) using both rabbit and human complement sources. Despite relatively high SBA titers and high levels of IgG against APS and OMVs in acute-phase patient sera, significant increases were seen in the early convalescent phase. Antibody concentrations returned to acute-phase levels in the late convalescent phase. Considering all patients' sera, a significant but low correlation (r = 0.46) was observed between SBA with rabbit complement (rSBA) using an ST-5 reference strain and SBA with human complement (hSBA) using an ST-7 strain from Ethiopia. While rSBA demonstrated a significant linear relation with IgG against APS, hSBA demonstrated significant linear relationships with IgG against both APS and OMV. This study indicates that antibodies against both outer membrane proteins and APS may be important in providing the protection induced during disease, as measured by hSBA. Therefore, outer membrane proteins could also have a role as components of future meningococcal vaccines for the African meningitis belt.

Clonal waves of Neisseria colonisation and disease in the African meningitis belt: eight- year longitudinal study in northern Ghana

BACKGROUND

The Kassena-Nankana District of northern Ghana lies in the African "meningitis belt" where epidemics of meningococcal meningitis have been reoccurring every eight to 12 years for the last 100 years. The dynamics of meningococcal colonisation and disease are incompletely understood, and hence we embarked on a long-term study to determine how levels of colonisation with different bacterial serogroups change over time, and how the patterns of disease relate to such changes.

METHODS AND FINDINGS

Between February 1998 and November 2005, pharyngeal carriage of Neisseria meningitidis in the Kassena-Nankana District was studied by twice-yearly colonisation surveys. Meningococcal disease was monitored throughout the eight-year study period, and patient isolates were compared to the colonisation isolates. The overall meningococcal colonisation rate of the study population was 6.0%. All culture-confirmed patient isolates and the majority of carriage isolates were associated with three sequential waves of colonisation with encapsulated (A ST5, X ST751, and A ST7) meningococci. Compared to industrialised countries, the colonising meningococcal population was less constant in genotype composition over time and was genetically less diverse during the peaks of the colonisation waves, and a smaller proportion of the isolates was nonserogroupable. We observed a broad age range in the healthy carriers, resembling that of meningitis patients during large disease epidemics.

CONCLUSIONS

The observed lack of a temporally stable and genetically diverse resident pharyngeal flora of meningococci might contribute to the susceptibility to meningococcal disease epidemics of residents in the African meningitis belt. Because capsular conjugate vaccines are known to impact meningococcal carriage, effects on herd immunity and potential serogroup replacement should be monitored following the introduction of such vaccines.

Multiple-locus variable-number tandem repeat analysis of Neisseria meningitidis yields groupings similar to those obtained by multilocus sequence typing

We identified many variable-number tandem repeat (VNTR) loci in the genomes of Neisseria meningitidis serogroups A, B, and C and utilized a number of these loci to develop a multiple-locus variable-number tandem repeat analysis (MLVA). Eighty-five N. meningitidis serogroup B and C isolates obtained from Dutch patients with invasive meningococcal disease and seven reference strains were analyzed using MLVA and multilocus sequence typing (MLST). MLVA, based on eight VNTR loci with limited variability in the number of repeats, yielded clustering of the strains similar to that obtained by MLST, with congruence between both methods amounting to 69%. The ability to recognize clonal complexes makes MLVA a valuable high-throughput method to serve as a tool complementary to MLST. Four highly variable VNTR loci were used in a second assay to analyze N. meningitidis serogroup C strains collected during an outbreak of meningococcal disease in The Netherlands. Typing based on the latter VNTR loci enabled differentiation of isolates with identical MLST sequence types and grouped epidemiologically related strains.

New rapid diagnostic tests for Neisseria meningitidis serogroups A, W135, C, and Y

BACKGROUND

Outbreaks of meningococcal meningitis (meningitis caused by Neisseria meningitidis) are a major public health concern in the African "meningitis belt," which includes 21 countries from Senegal to Ethiopia. Of the several species that can cause meningitis, N. meningitidis is the most important cause of epidemics in this region. In choosing the appropriate vaccine, accurate N. meningitidis serogroup determination is key. To this end, we developed and evaluated two duplex rapid diagnostic tests (RDTs) for detecting N. meningitidis polysaccharide (PS) antigens of several important serogroups.

METHODS AND FINDINGS

Mouse monoclonal IgG antibodies against N. meningitidis PS A, W135/Y, Y, and C were used to develop two immunochromatography duplex RDTs, RDT1 (to detect serogroups A and W135/Y) and RDT2 (to detect serogroups C and Y). Standards for Reporting of Diagnostic Accuracy criteria were used to determine diagnostic accuracy of RDTs on reference strains and cerebrospinal fluid (CSF) samples using culture and PCR, respectively, as reference tests. The cutoffs were 10(5) cfu/ml for reference strains and 1 ng/ml for PS. Sensitivities and specificities were 100% for reference strains, and 93.8%-100% for CSF serogroups A, W135, and Y in CSF. For CSF serogroup A, the positive and negative likelihood ratios (+/- 95% confidence intervals [CIs]) were 31.867 (16.1-63.1) and 0.065 (0.04-0.104), respectively, and the diagnostic odds ratio (+/- 95% CI) was 492.9 (207.2-1,172.5). For CSF serogroups W135 and Y, the positive likelihood ratio was 159.6 (51.7-493.3) Both RDTs were equally reliable at 25 degrees C and 45 degrees C.

CONCLUSIONS

These RDTs are important new bedside diagnostic tools for surveillance of meningococcus serogroups A and W135, the two serogroups that are responsible for major epidemics in Africa.

Scaling up of PCR-based surveillance of bacterial meningitis in the African meningitis belt: indisputable benefits of multiplex PCR assay in Niger

The absence of reliable laboratories for culture of Neisseria meningitidis, Haemophilus influenzae and Streptococcus pneumoniae, the three main causes of bacterial meningitis in Africa, hampers microbiological surveillance in these countries. To compensate for this situation in Niger, a multiplex single-tube PCR method has been implemented at a central level to test cerebrospinal fluid (CSF) samples. The overall confirmation rate for PCR (N=3791) was 40.8% compared with 16.0% for culture (N=945) (P<10(-6)). Among 850 CSF specimens tested by both methods, the overall confirmation rate was 29.4% for PCR and 16.4% for culture (P<10(-8)). PCR was also efficient for the CSF specimens stored in Trans-isolate medium. In conclusion, PCR assay is currently a key tool in Africa to improve microbiological surveillance of bacterial meningitis.

Multilocus sequence typing: Data analysis in clinical microbiology and public health

Numerous computer-based statistical packages have been developed in recent years and it has become easier to analyze nucleotide sequence data and gather subsequent information that would not normally be available. Multilocus sequence typing (MLST) is used for characterizing isolates of bacterial and fungal species and uses nucleotide sequences of internal fragments of housekeeping genes. This method is finding a place in clinical microbiology and public health by providing data for epidemiological surveillance and development of vaccine policy. It adds greatly to our knowledge of the genetic variation that can occur within a species and has therefore been used for studies of population biology. Analysis requires the detailed interpretation of nucleotide sequence data obtained from housekeeping and nonhousekeeping genes. This is due to the amount of data generated from nucleotide sequencing and the information generated from an array of analytical tools improves our understanding of bacterial pathogens. This can benefit public health interventions and the development of enhanced therapies and vaccines. This review concentrates on the analytical tools used in MLST and their use in the clinical microbiology and public health fields.

Étude de souches de Neisseria meningitidis sérogroupe B isolées à Casablanca par multilocus sequence typing et électrophorèse en champ pulsé

A previous study showed that B:4:P1.15 was the most frequent phenotype of Neisseria meningitidis isolated in Casablanca (Morocco). To determine if there was an epidemic clone, MLST and PFGE were used to compare 13 B:4:P1.15 strains isolated from September 1999 to December 2000. MLST showed 4 Sequence Types (ST): ST-33 was the most frequent ST (9/13 strains) and 4 strains belonged to 3 newly described STs. Twelve stains belonged to ST-32 complex, and one strain presenting a new ST (ST-2502) did not belong to any known ST complex. The analysis by PFGE showed that the strains were subdivided into 7 clusters, and that there was no epidemic clone. MLST is useful for long-term epidemiological studies on N. meningitidis strains from varied geographical origins. PFGE seemed to be well adapted to the comparison of a small number of strains isolated during a short period within a defined community.

Characterization of Neisseria meningitidis isolates from recent outbreaks in Ethiopia and comparison with those recovered during the epidemic of 1988 to 1989

The objectives of this study were to collect and characterize epidemic meningococcal isolates from Ethiopia from 2002 to 2003 and to compare them to 21 strains recovered during the previous large epidemic of 1988 to 1989. Ninety-five patients in all age groups with clinical signs of meningitis and a turbid cerebrospinal fluid (CSF) sample were included in the study of isolates from 2002 to 2003. Seventy-one patients (74.7%) were confirmed as having Neisseria meningitidis either by culture (n = 40) or by porA PCR (n = 31) of their CSF. The overall case fatality rate (CFR) was 11.6%; the N. meningitidis-specific CFR was 4.2%. All 40 strains were fully susceptible to all antibiotics tested except sulfonamide, were serotyped as A:4/21:P1.20,9, and belonged to sequence type 7 (ST-7). The strains from 1988 to 1989 were also equally susceptible and were characterized as A:4/21:P1.20,9, but they belonged to ST-5. Antigenic characterization of the strains revealed differences in the repertoire of lipooligosaccharides and Opa proteins between the old and the recent strains. PCR analysis of the nine lgt genes revealed the presence of the lgtAHFG genes in both old and recent strains; lgtB was present in only some of the strains, but no correlation with sequence type was observed. Further analysis showed that in addition to their pgm alleles, the Ethiopian ST-5 and ST-7 strains also differed in their tbpB, opa, fetA, and lgtA genes. The occurrence of new antigenic structures in strains sharing the same serogroup, PorA, and PorB may help explain the replacement of ST-5 by ST-7 in the African meningitis belt.

Molecular epidemiology and emergence of worldwide epidemic clones of Neisseria meningitidis in Taiwan

Background

Meningococcal disease is infrequently found in Taiwan, a country with 23 million people. Between 1996 and 2002, 17 to 81 clinical cases of the disease were reported annually. Reported cases dramatically increased in 2001–2002. Our record shows that only serogroup B and W135 meningococci have been isolated from patients with meningococcal disease until 2000. However, serogroup A, C and Y meningococci were detected for the first time in 2001 and continued to cause disease through 2002. Most of serogroup Y meningococcus infections localized in Central Taiwan in 2001, indicating that a small-scale outbreak of meningococcal disease had occurred. The occurrence of a meningococcal disease outbreak and the emergence of new meningococcal strains are of public health concern.

Methods

Neisseria meningitidis isolates from patients with meningococcal disease from 1996 to 2002 were collected and characterized by serogrouping, pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). The genetic relatedness and clonal relationship between the isolates were analyzed by using the PFGE patterns and the allelic profiles of the sequence types (STs).

Results

Serogroups A, B, C, W135, Y, and non-serogroupable Neisseria meningitidis were, respectively, responsible for 2%, 50%, 2%, 35%, 9%, and 2% of 158 culture-confirmed cases of meningococcal disease in 1996–2002. Among 100 N. meningitidis isolates available for PFGE and MLST analyses, 51 different PFGE patterns and 30 STs were identified with discriminatory indices of 0.95 and 0.87, respectively. Of the 30 STs, 21 were newly identified and of which 19 were found in serogroup B isolates. A total of 40 PFGE patterns were identified in 52 serogroup B isolates with the patterns distributed over several distinct clusters. In contrast, the isolates within each of the serogroups A, C, W135, and Y shared high levels of PFGE pattern similarity. Analysis of the allelic profile of the 30 STs suggested the serogroup B isolates be assigned into 5 clonally related groups/ clonal complexes and 7 unique clones. The ST-41/44 complex/Lineage 3, and the ST-3439 and ST-3200 groups represented 79% of the serogroup B meningococci. In contrast, isolates within serogroups A, serogroup W135 (and C), and serogroup Y, respectively, simply belonged to ST-7, ST-11, and ST-23 clones.

Conclusion

Our data suggested that serogroup B isolates were derived from several distinct lineages, most of which could either be indigenous or were introduced into Taiwan a long time ago. The serogroup A, W135 (and C), and Y isolates, respectively, belonged to the ST-7, ST-11, and ST-23, and the represented clones that are currently the major circulating clones in the world and are introduced into Taiwan more recently. The emergence of serogroup A, C and Y strains contributed partly to the increase in cases of meningococcal disease in 2001–2002.

Molecular epidemiology of neisseria meningitidis isolated in the African Meningitis Belt between 1988 and 2003 shows dominance of sequence type 5 (ST-5) and ST-11 complexes

At the two World Health Organization Collaborating Centers for Reference and Research on Meningococci in Marseilles, France, and Oslo, Norway, the multilocus sequence typing technique was used for the characterization of a total of 357 strains of meningococci isolated from meningitis cases in 13 African countries of the meningitis belt between 1988 and 2003. Among these strains, 278 of 357 (77.9%) belonged to the sequence type 5 (ST-5) complex; 23.2% were ST-5 and 53.5% were ST-7. ST-5 was probably introduced in Africa in 1987 and was responsible for most of the meningitis cases between 1988 and 2001. ST-7 emerged in the mid-1990s and has totally replaced ST-5 since 2002. These two STs characterized serogroup A strains and have been responsible for hundreds of thousands of cases. Fifty-two strains (14.3%) belonged to the ST-11 complex. The ST-11 complex was characterized by serogroup W135, which has been responsible for an increasing number of sporadic cases since 2000 and the first W135 epidemic ever seen in Africa (in Burkina Faso in 2002). Identification of W135 ST-11 strains in many countries is a great concern for the region. Apart from these two major clonal complexes, a few other clones, such as ST-2881, ST-181, and ST-751, were sporadically detected. Careful surveys for these clones need to be conducted, but at present they play only a minor role in the overall epidemiology of meningococcal meningitis.

Epidemiological patterns of meningococcal meningitis in Niger in 2003 and 2004: under the threat of N. meningitidis serogroup W135

Since the Neisseria meningitidis serogroup W135 epidemic in Burkina Faso in 2002, the neighbouring countries dread undergoing outbreaks. Niger has strongly enhanced the microbiological surveillance, especially by adding the polymerase chain reaction (PCR) assay to the national framework of the surveillance system. During the 2003 epidemic season, 8113 clinically suspected cases of meningitis were notified and nine districts of the 42 crossed the epidemic threshold, while during the 2004 season, the number of cases was 3521 and four districts notified epidemics. In 2003 and 2004, serogroup A was identified in most N. meningitidis from cerebrospinal fluid (CSF) specimens (89.7% of 759 and 87.2% of 406, respectively). Although serogroup W135 represented only 8.3% of the meningococcal meningitis in 2003 and 7.9% in 2004, and was not involved in outbreaks, it was widespread in various areas of the country. In the regions that notified epidemics, the proportion of serogroup W135 was tiny while it exceeded 40% in several non-epidemic regions. Despite the wide distribution of W135 serogroup in Niger and the fears expressed in 2001, the threat of a large epidemic caused by N. meningitidis W135 seems to have been averted in Niger so far. There is no clear indication whether this serogroup will play a lasting role in the epidemiology of meningococcal meningitis or not. As early as in the 1990s, a significant but transient increase in the incidence of N. meningitidis serogroup X was observed. Close microbiological surveillance is crucial for monitoring the threat and for identifying at the earliest the serogroups involved in epidemics.

Development and characterisation of outer membrane vesicle vaccines against serogroup A Neisseria meningitidis

Neisseria meningitidis bacteria of serogroup A are causing recurring meningitis epidemics on the African continent. An outer membrane vesicle (OMV) vaccine against serogroup A meningococci made from a subgroup III serogroup A meningococcal strain was previously shown to induce antibodies with serum bactericidal activity (SBA) in mice. We have here further investigated the properties of OMV vaccines made from five different subgroup III serogroup A meningococcal strains grown in a synthetic medium with low iron content. In addition to the major outer membrane proteins (PorA, PorB, RmpM, Opa and OpcA), small amounts of the NadA, TdfH, Omp85, FetA, FbpA and NspA outer membrane proteins, as well as lipooligosaccharides, were detected in the vaccines. The OMV vaccines were used to immunise mice. Anti-meningococcal IgG antibodies in the mouse sera were analysed by immunoblotting and by enzyme-linked immunosorbent assay against OMVs, and against live meningococcal cells in SBA and a flow-cytometric assay. The vaccines induced antibodies with high SBA and opsonophagocytic activity. The strongest IgG responses were directed against PorA. Significant SBA responses were also observed against a subgroup III strain, which did not express PorA, whereas no SBA was observed against a clone IV-1 serogroup A strain. An OMV vaccine from serogroup A meningococci may be an alternative to polysaccharide and conjugate polysaccharide vaccines for Africa.

Molecular epidemiology of meningococci isolated in Niger in 2003 shows serogroup A sequence type (ST)-7 and serogroup W135 ST-11 or ST-2881 strains

In 2003, in the Zinder and Maradi regions (Niger), epidemics were due to serogroup A:4:P1.9 meningococci belonging to sequence type 7 (ST-7). In Niamey, only sporadic cases were reported: 55% of the meningococcus strains were in serogroup A, and 38% were in serogroup W135 and could be placed in ST-11, identical to the 2002 Burkina Faso epidemic clone, and in ST-2881, a new ST.

Immunogenicity and bactericidal activity in mice of an outer membrane protein vesicle vaccine against Neisseria meningitidis serogroup A disease

Serogroup A Neisseria meningitidis organisms of the subgroup III have caused epidemics of meningitis in sub-Saharan Africa since their introduction into the continent in 1987. The population structure of these bacteria is basically clonal, and these meningococci are strikingly similar in their major outer membrane antigens PorA and PorB. Protein-based vaccines might be an alternative to prevent epidemics caused by these meningococci; thus, we developed an outer membrane vesicle (OMV) vaccine from a serogroup A meningococcal strain of subgroup III. The serogroup A OMV vaccine was highly immunogenic in mice and elicited significant bactericidal activity towards several other serogroup A meningococci of subgroup III. The IgG antibodies generated were in immunoblot shown to be mainly directed towards the PorA outer membrane protein. The results presented demonstrate the potential of an OMV vaccine as an optional strategy to protect against meningococcal disease caused by serogroup A in Africa.

Immunogenicity, safety, and memory of different schedules of Neisseria meningitidis A/C-diphtheria toxoid conjugate vaccine in infants in Niger

We studied one to four doses of meningococcal polysaccharides A and C conjugated to diphtheria toxoid (Men D) versus A/C polysaccharide (Men PS) vaccine in 618 infants in Niger. Men PS at 24 months permitted evaluating memory. Two Men D doses (at 3 and 9 months) induced higher serum bactericidal activity (SBA) than other regimens. SBA titers after Men PS at 24 months were higher in those given Men D in infancy versus Men PS. While responses were lower for serogroup C, hyporesponsiveness was not evident. Men D was well-tolerated. A single Men D dose in infancy appeared to induce memory.

Molecular characterisation of group A Neisseria meningitidis isolated in Sudan 1985-2001

A total of 33 group A Neisseria meningitidis (Mc) isolates, collected in Sudan between 1985 and 2001, were studied in order to describe the changes over time in a country within the meningitis belt of Africa. The isolates were characterised by traditional phenotypic methods (serogrouping, serotyping, serosubtyping and antibiogram) and molecular techniques (genosubtyping, pulsed-field gel electrophoresis [PFGE] with restriction endonucleases SpeI and NheI, and multilocus sequence typing [MLST]). Three clones of group A Mc were identified: one before 1988 (sulphadiazine sensitive, serotype 4, genosubtype P1.7,13-1,35-1, sequence type 4 [ST-4]); another during and after the 1988 epidemic (sulphadiazine resistant, serotype 4, genosubtype P1.20,9,35-1, ST-5); and a third causing the 1999 epidemic (sulphadiazine resistant, serotype 4, genosubtype P1.20,9,35-1, ST-7). The first clone showed major differences compared to the other two. The second and third clones had many similarities with differences in only a single gene (pgm) in the MLST (47 of the 450 bp) but significant other differences according to the PFGE patterns. Within the clones, genosubtyping and MLST gave identical information (except one base substitution in the aroE gene in one isolate). However, the PFGE patterns showed changes over time within the clones, where SpeI revealed somewhat more diversity than NheI.

W135 in Africa: origins, problems and perspectives

Serogroup A meningococci have been the major cause of epidemic meningococcal disease in Africa throughout the last 100 years. The reasons for this unusual pattern of behaviour have remained unclear and there remain significant debates and logistic difficulties around the appropriate use of plain A/C polysaccharide vaccination to control African meningococcal disease. Since the Hajj pilgrimage of 2000 serogroup W135 organisms (of the ST-11 clonal complex) have emerged as a further significant cause of epidemic meningococcal disease in Africa. Whilst advances in molecular biological and genetic techniques have yielded increasing insights into meningococcal epidemiology there remain many unanswered questions about the reason for the emergence of a serogroup W135 clone capable of epidemic behaviour and in particular its relation to past use of group A/C polysaccharide. The high cost and short supply of quadrivalent (A,C,Y, W135) vaccine to protect against W135 disease has added to what was already the significant burden of controlling serogroup A meningococcal disease. The ability of virulent meningococcal clones to acquire new capsule types raises further concerns about the future nature of meningococcal disease in Africa and the strategies of vaccination use and development necessary to contain it.

The duality of virulence and transmissibility in Neisseria meningitidis

Neisseria meningitidis is a commensal bacterium of the human nasopharynx that occasionally provokes invasive disease. Carriage strains of N. meningitidis are heterogeneous, more frequent in nature and are transmitted among carriers. Disease is not a part of this transmission cycle and is caused by virulent strains. N. meningitidis is highly variable and variants that are modified in their virulence and/or transmissibility are continually generated. These events probably occur frequently, thus explaining not only the heterogeneous nature of meningococcal populations in carriers but probably also the evolutionary success of this human-restricted bacterium.

Fit genotypes and escape variants of subgroup III Neisseria meningitidis during three pandemics of epidemic meningitis

The genetic variability at six polymorphic loci was examined within a global collection of 502 isolates of subgroup III, serogroup A Neisseria meningitidis. Nine "genoclouds" were identified, consisting of genotypes that were isolated repeatedly plus 48 descendent genotypes that were isolated rarely. These genoclouds have caused three pandemic waves of disease since the mid-1960s, the most recent of which was imported from East Asia to Europe and Africa in the mid-1990s. Many of the genotypes are escape variants, resulting from positive selection that we attribute to herd immunity. Despite positive selection, most escape variants are less fit than their parents and are lost because of competition and bottlenecks during spread from country to country. Competition between fit genotypes results in dramatic changes in population composition over short time periods.