Prospects for vaccine prevention of meningococcal infection

PorA types in Neisseria meningitidis serogroup B isolated in Argentina from 2001 to 2003: implications for the design of an outer membrane protein-based vaccine

Identification ofNeisseria meningitidisPorA types remains important, as the PorA protein is a major immunogenic component of several meningococcal vaccines under development. In this study, 191N. meningitidisserogroup B isolates collected in Argentina through active laboratory-based surveillance from 2001 to 2003 were serosubtyped. Nucleotide sequences of theporAvariable region 1 (VR1) and VR2 regions were determined in 52 non-serosubtypeable isolates. A substantial number of distinct VR types were identified, and a new VR2 variant from the P1.16 family was described. This is the first report describing PorA types inN. meningitidisserogroup B isolates in Argentina. Furthermore, the wide diversity of subtypes detected by serosubtyping and genosubtyping reveals the difficulty in designing a useful outer-membrane vaccine applicable in this country. A possible mechanism responsible for altered PorA expression was analysed in two PorA types.

Risk factors for meningococcal disease in students in grades 9-12

BACKGROUND

Meningococcal disease is a serious problem in adolescents, including high school students. Universal immunization of adolescents with meningococcal conjugate vaccine was recently recommended. We studied risk factors for meningococcal disease in students in grades 9-12.

METHODS

This was a matched case-control study using surveillance for meningococcal disease in students in grades 9-12 in sites throughout the United States. For each case-patient, up to 4 controls were selected from the home room classroom. All subjects answered an extensive questionnaire. Logistic regression was performed to identify risk factors associated with meningococcal disease. Meningococcal isolates were characterized.

RESULTS

Of 69 eligible patients, 49 (71%) were enrolled and had at least 1 control. Isolates were available for 59 (86%) cases. Attending at least 1 barbeque or picnic [matched odds ratio (MOR): 0.26, P value = 0.003] or school dance (MOR: 0.30, P = 0.04) were independently associated with decreased risk of meningococcal disease. Male gender (MOR: 2.94, P = 0.009), upper respiratory infection symptoms (MOR: 2.43, P = 0.04), marijuana use (MOR: 4.21, P = 0.009), and nightclub/disco attendance (MOR: 3.30, P = 0.04) were associated with increased risk. Among 54 students not from Oregon (where serogroup B strains predominate) with available serogroup, 38 (73.1%) cases were potentially vaccine preventable: 18 (34.6%) serogroup C, 19 (36.5%) serogroup Y, and 1 (1.9%) serogroup W-135.

CONCLUSIONS

Certain behaviors increase the risk of meningococcal infection, whereas others are associated with decreased risk. Most meningococcal disease in high school students can be prevented if recommendations on use of meningococcal conjugate vaccine are implemented.

The differential response of human dendritic cells to live and killed Neisseria meningitidis

There is currently no effective vaccine for Neisseria meningitidis (Nm) serogroup B. Generation of optimal immune responses to meningococci could be achieved by targeting meningococcal antigens to human dendritic cells (DCs). Recent studies have shown that diverse DC responses and subsequent generation of protective immunity can be observed if the microbes are viable or killed. This is important because the host is likely to be exposed to both live and killed bacteria during natural infection. There are currently few data on comparative DC responses to live and killed meningococci. We show here that exposure of human DC to live meningococci does not result in a typical maturation response, as determined by the failure to upregulate CD40, CD86, HLA-DR and HLA-Class I. Despite this, live meningococci were potent inducers of IL-12 and IL-10, although the ratios of these cytokines differed from those to killed organisms. Our data also suggest that enhanced phagocytosis of killed organisms compared with live may be responsible for the differential cytokine responses, involving an autocrine IL-10-dependent mechanism. The consequences of these findings upon the effectiveness of antigen presentation and T-cell responses are currently under investigation.

Intranasal vaccines for protection against respiratory and systemic bacterial infections

More than 4 million deaths per year are due to respiratory diseases. Although licensed vaccines are available, bacteria, such as Streptococcus pneumoniae, Haemophilus influenzae, Mycobacterium tuberculosis, Bordetella pertussis and Neisseria meningiditis, among others, continue to be the major agents of diseases in young children, the elderly and/or immunocompromized individuals. Following respiratory tract infection, some microorganisms may also invade the epithelial tissue, achieving systemic circulation and/or other organs. Nasal administration of different antigen formulations has shown promising results in the induction of immune responses and the defeat of the pathogens at the site of infection. This review will focus on the main nasal vaccine strategies and technologies being investigated against the most common infections caused by respiratory bacteria.

Bacterial meningitis: the impact of vaccination

Acute bacterial meningitis remains an important cause of morbidity and mortality in children. Children <2 years of age are particularly susceptible to infection with encapsulated bacteria due to their immature response to polysaccharide antigens. Conjugate vaccines, which induce T cell memory, can provide immunological protection for these children. The Haemophilus influenzae type b (Hib) conjugate vaccine was the first such vaccine to become available. The efficacy of the vaccine has been quoted as being 98%. Its introduction was followed by a dramatic decrease in the incidence of all invasive Hib disease, including meningitis. This reduction was in part due to the ability of these vaccines to reduce nasopharyngeal carriage of the organism and thereby induce herd immunity. Different Hib vaccines use a variety of protein carriers and differ in their immunogenicity and efficacy. The most suitable vaccine needs to be determined according to the local epidemiology of Hib disease. Commercial combination vaccines may lead to lower antibody levels. A recent increase in the incidence of Hib disease in the UK highlights the importance of continued surveillance and the need for booster vaccinations to ensure continued protection. Conjugate vaccines to Streptococcus pneumoniae and Neisseria meningitidis have been developed. The introduction of a pneumococcal conjugate vaccine in the US has led to a decrease in the rate of infection by nearly 60% in children <5 years of age. A reduction in pneumococcal carriage may also modify disease epidemiology. The UK introduced the conjugate meningococcal C vaccine into its infant schedule with a corresponding reduction in N. meningitidis group C disease. A recent decrease in the effectiveness of the vaccine, however, suggests a booster may be necessary in the future. Our present understanding of the immunology of conjugate vaccines is far from complete. Developed countries have introduced conjugate vaccines into their immunisation schedules to prevent bacterial meningitis; however, their high cost precludes their use in many developing countries. Progress needs to be made in order to get these highly effective vaccines to those areas that need them.

Neisserial outer membrane vesicles bind the coinhibitory receptor carcinoembryonic antigen-related cellular adhesion molecule 1 and suppress CD4+ T lymphocyte function

Pathogenic Neisseria bacteria naturally liberate outer membrane "blebs," which are presumed to contribute to pathology, and the detergent-extracted outer membrane vesicles (OMVs) from Neisseria meningitidis are currently employed as meningococcal vaccines in humans. While the composition of these vesicles reflects the bacteria from which they are derived, the functions of many of their constituent proteins remain unexplored. The neisserial colony opacity-associated Opa proteins function as adhesins, the majority of which mediate bacterial attachment to human carcinoembryonic antigen-related cellular adhesion molecules (CEACAMs). Herein, we demonstrate that the Opa proteins within OMV preparations retain the capacity to bind the immunoreceptor tyrosine-based inhibitory motif-containing coinhibitory receptor CEACAM1. When CD4(+) T lymphocytes were exposed to OMVs from Opa-expressing bacteria, their activation and proliferation in response to a variety of stimuli were effectively halted. This potent immunosuppressive effect suggests that localized infection will generate a "zone of inhibition" resulting from the diffusion of membrane blebs into the surrounding tissues. Moreover, it demonstrates that OMV-based vaccines must be developed from strains that lack CEACAM1-binding Opa variants.

Living in a changing environment: insights into host adaptation in Neisseria meningitidis from comparative genomics

Neisseria meningitidis (the meningococcus) colonizes the human nasopharynx of about 10% of the human population. However, for reasons that are still mostly unknown meningococci occasionally enter the cerebrospinal fluid leading to often fatal bacterial meningitis especially in children and young adults. The genetic basis for the observed differences in the pathogenic potential of different strains has only partially been unravelled so far. With the advent of whole genome sequencing technologies, complete genome sequences from three pathogenic meningococcal strains have become available and allow for a comprehensive analysis of the genomic and genetic differences occurring within this species. In this review, the general properties of the meningococcal genomes so far sequenced is given with an emphasis on the chromosomal rearrangements that have occurred, and the genomic islands and prophages that have been identified. The concomitant development of microarray technology for comparative genome hybridization studies of a large set of different meningococcal isolates as well as strains from other Neisseria species has extended our understanding of meningococcal population genetics on a genome-wide scale thus bridging the gap between meningococcal epidemiology and genomics. Finally, we briefly discuss the potential impact of meningococcal life style on its genome architecture and how in turn this genomic make-up might lead to a virulent phenotype making N. meningitidis an accidental pathogen. The overall properties of the meningococcal genome are characterized by genomic variability and instability, resulting in increased functional flexibility within this species.

Assessment of a two-step nucleic acid amplification assay for detection of Neisseria meningitidis followed by capsular genogrouping

Immediate prevention of meningococcal disease relies in part on the prompt treatment with antibiotics of household and other close contacts of cases; however intervention with effective vaccination relies on identification of serogroup-causing strains. Parenteral antibiotic for patient with suspected meningococcal disease before hospital admission is currently recommended. Laboratory standard methods are hindered by failure to detect bacteria by this medical approach to improve patient prognosis. We assessed two polymerase chain reaction (PCR) assays to detect (crgA) and define the serogroups (siaD, orf-2, and ctrA) of Neisseria meningitidis in 120 cerebrospinal fluid (CSF) samples from positive cases (culture or antigen detection or direct smear). The PCR sensitivity for the identification of N. meningitidis was 100% (95% confidence interval, CI, 96-100%) compared to a sensitivity of 46% for culture (95% CI 37-55%), 61% for latex agglutination test (95% CI 52-70%), and 68% for Gram stain (95% CI 59-76%); PCR specificity was 97% (95% CI 82-100%). PCR correctly identified the serogroups A, B, C, W135, Y, and X in CSF samples with a sensitivity of 88% (95% CI 80-93%); the primer sets were 100% specific. The introduction of PCR-based assays shall increase laboratory confirmed cases, consequently enhancing surveillance of meningococcal disease.

Protective meningococcal capsular polysaccharide epitopes and the role of O acetylation

Previous studies with group C meningococcal polysaccharide-tetanus toxoid (GCMP-TT) conjugates had suggested that the GCMP O-acetyl group masked the protective epitope for group C meningococci through steric hindrance or altered conformations. For this report, we confirmed this phenomenon and performed comparative studies with group Y meningococcal polysaccharide (GYMP)-TT to determine whether it might extend to other serogroups. The de-O-acetylated (dOA) polysaccharides (PSs) resulted in higher serum bactericidal activities (SBA) towards the O-acetylated (OA) meningococcal strains from the respective serogroups. High-resolution H-nuclear magnetic resonance spectroscopy at 500 MHz and competitive inhibition serum bactericidal assays were used to characterize the nature of the protective epitope. In head-to-head comparisons with OA PSs as SBA inhibitors, the dOA PSs provided 10 to 1,000 times better inhibition for GCMP in human and mouse antisera and 6 to 13 times better inhibition for GYMP in mouse antisera, using OA strains in all assays. In addition, the SBA for OA strains was highly correlated with dOA PS-specific immunoglobulin G (r=0.72 to 0.98) for both GCMP and GYMP. The results suggest that there may be a generalized role for the O-acetyl group to provide an epitope of misdirected immunogenicity for meningococcal PS capsules, enabling escape from immune surveillance. In addition to greater chemical consistency, the dOA forms of GCMP and GYMP conjugate vaccines endow greater immunologic competence to the PSs, rendering them capable of eliciting higher levels of functional antibodies toward the protective epitopes.

Preparedness for infectious threats: public-private partnership to develop an affordable vaccine for an emergent threat: the trivalent Neisseria meningitidis ACW135 polysaccharide vaccine

With the emergence of epidemic Neisseria meningitidis W135 meningitis in Burkina Faso during early 2002, the public health community was faced with the challenge of providing access to an appropriate and affordable vaccine in time for the upcoming 2003 epidemic season. Recognizing the implications of the emergent threat, the World Health Organization developed a strategy, established a public-private partnership to provide the needed vaccine, and then ensured that a stockpile was available for future use. The trivalent N meningitidis ACW135 polysaccharide vaccine that resulted is now one of the primary tools for epidemic response in African meningitis belt countries. It will remain so for the foreseeable future and until appropriate and affordable conjugate vaccines become part of national immunization programs in the region.

Special infectious disease risks of expatriates and long-term travelers in tropical countries. Part II: infections other than malaria

A wide range of viral, bacterial, and protozoal diseases pose risk to long-term tropical travelers. Risk varies geographically and with lifestyle. For some infections, risk increases with duration of stay, coming to resemble that of the local population. Risk management strategies include vaccination, chemoprophylaxis, avoidance measures, and screening, where appropriate. Vaccination against hepatitis A and B, typhoid, and rabies is recommended for all long-term travelers to (sub-)tropical areas. Lowering of the vaccination threshold for Japanese encephalitis is suggested. Meningococcal disease is rare in travelers, but vaccination is safe and acceptable. The efficacy of Bacillus Calmette-Guérin (BCG) is uncertain; immunological testing avoids BCG's confounding of tuberculin testing. Diarrhea is common, and self-treatment may be recommended. Sexually transmitted infections including human immunodeficiency virus (HIV) are serious risks; education, screening, and HIV postexposure prophylaxis following involuntary exposure are recommended. Many infections are chronic or asymptomatic, and appropriate screening is recommended on return or after prolonged exposure.

Prospects for prevention of childhood infections by maternal immunization

PURPOSE OF REVIEW

To review the literature on using maternal immunization as a strategy to prevent infections in young infants aged below 6 months

RECENT FINDINGS

Maternal immunization continues to reduce the incidence of neonatal tetanus worldwide. Despite increased influenza-related morbidity and mortality in pregnant women and in infants aged less than 6 months, compliance with US recommendations for immunization against influenza in pregnancy is poor. Polysaccharide vaccines against Haemophilus influenzae type b, Streptococcus pneumoniae and Neisseria meningitidis are safe and immunogenic in pregnancy. Protein conjugate vaccines against these infections would be likely to induce higher maternal antibody levels and improve placental transport, thereby further reducing the maternal and infant disease burden. Further studies of acellular pertussis vaccines for use in adolescents and adults should evaluate if maternal immunization could prevent life-threatening pertussis in young infants. Maternal immunization against group B streptococcus is projected to be superior to screening and/or chemoprophylaxis strategies in decreasing infant disease.

SUMMARY

Maternal immunization, with the passage of protective antibody to infants, is a potential strategy to prevent infection in infants who have not completed their primary immunization series from both specific infections of infancy and vaccine-preventable illnesses. Further evaluation of this strategy is supported by medical literature, but liability and educational barriers exist.

Health risks at the Hajj

Annually, millions of Muslims embark on a religious pilgrimage called the "Hajj" to Mecca in Saudi Arabia. The mass migration during the Hajj is unparalleled in scale, and pilgrims face numerous health hazards. The extreme congestion of people and vehicles during this time amplifies health risks, such as those from infectious diseases, that vary each year. Since the Hajj is dictated by the lunar calendar, which is shorter than the Gregorian calendar, it presents public-health policy planners with a moving target, demanding constant preparedness. We review the communicable and non-communicable hazards that pilgrims face. With the rise in global travel, preventing disease transmission has become paramount to avoid the spread of infectious diseases, including SARS (severe acute respiratory syndrome), avian influenza, and haemorrhagic fever. We examine the response of clinicians, the Saudi Ministry of Health, and Hajj authorities to these unique problems, and list health recommendations for prospective pilgrims.