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{{WPBiography
{{Taxobox
|living=yes
| color = lightgrey
|class=Stub
| name = ''Neisseria meningitidis''
|priority=
| image= Neisseria meningitidis.jpg
|auto=yes
| image_caption=[[micrograph|Photomicrograph]] of ''N. meningitidis''
|a&e-work-group=yes
| regnum = [[Bacterium|Bacteria]]
| phylum = [[Proteobacteria]]
| classis = [[Beta Proteobacteria]]
| ordo = [[Neisseriaceae|Neisseriales]]
| familia = [[Neisseriaceae]]
| genus = ''[[Neisseria]]''
| species = '''''N. meningitidis'''''
| binomial = ''Neisseria meningitidis''
| binomial_authority = Albrecht & Ghon 1901
}}
}}
{{WikiProject Journalism}}
'''''Neisseria meningitidis''''', also simply known as ''meningococcus'', is a heterotrophic [[gram-negative]] [[diplococcus|diplococcal]] [[bacterium]] best known for its role in [[meningitis]]<ref name=Sherris>{{cite book | author = Ryan KJ; Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th ed. | publisher = McGraw Hill | year = 2004 | pages = 329&ndash;333 | id = ISBN 0838585299 }}</ref> and other forms of [[meningococcal disease]] such as meningococcemia.

It only infects humans; there is no animal [[Natural reservoir|reservoir]], and it exists as normal flora in the [[nasopharynx]] of up to 40% of adults. It causes the only form of bacterial meningitis known to cause [[epidemic]]s. <!--This disease has also sometimes been found to eat away at severe burns and open wounds. Statistics show that this disease targets left handed people more than right. -->

== Strains ==
There are many strains of meningococcus, which are differentiated based on the chemical composition of their polysaccharide capsule. The most clinically important are A, B, C, X, Y and W135:
* ''A'' occurs most often in sub-sahara Africa and [[vaccination]] is recommended prior to travel with the ''Men A&C'' vaccine.
* ''B'' is the most lethal form, comprising 40% of UK cases. The changing nature of the B group has prevented formation of a general B vaccine in the UK. However there has been developed the vaccine [[MeNZB]] against a specific strain of group B meningococcus, currently being used to control an epidemic in [[New Zealand]]. Previously, an earlier neisseria meningitidis vaccine against subtype B was not effective because the sialic acid residues of the capsule are similar to humans.
* ''C'' caused approximately 60% of UK cases before the introduction of successful vaccination program for infants. Previously the unconjugated ''C'' component of ''Men A&C'' was ineffective in those under 2 years. The development of a conjugated form (''Men C conj'') was needed to provoke infant immunity.
* ''W135'' is particularly a problem for those undergoing annual pilgrimage to [[Mecca]]. It is a requirement of [[Saudi Arabia]] that all those intending to go on [[Hajj]] have a certificate of Men W135 vaccination.
* ''X'': A broad outbreak of meningitis caused by serogroup X was reported in [[Niger]] in 2006.<ref>{{cite journal | author=Boisier P, Nicolas P, Djibo S, ''et al.'' | title=Meningococcal Meningitis: Unprecedented Incidence of Serogroup X–Related Cases in 2006 in Niger | journal=Clin Infect Dis | year=2007 | volume=44 | pages=657–63 | url=http://www.journals.uchicago.edu/CID/journal/issues/v44n5/41097/41097.html | doi=10.1086/511646 | format={{Dead link|date=May 2008}} }}</ref> This outbreak is particularly worrying because there is not currently any vaccine against this strain.
* ''Y'': In the last decade serogroup Y has emerged as a cause of disease in Northern America

Other strains include 29-E, H, I, K, L, and Z.

==Infection==
Meningococcus is spread through the exchange of saliva and other respiratory secretions during activities like coughing, kissing, and chewing on toys. Though it initially produces with general symptoms like [[fatigue (medical)|fatigue]], it can rapidly progress from fever, headache and [[neck stiffness]] to [[coma]] and death. [[Death]] occurs in approximately 10% of cases.{{Fact|date=July 2007}} Those with impaired immunity may be at particular risk of meningococcus (e.g. those with [[nephrotic syndrome]] or [[splenectomy]]; vaccines are given in cases of [[asplenia|removed or non-functioning spleens]]).

Suspicion of meningitis is a [[medical emergency]] and immediate medical assessment is recommended. Current guidance in the [[United Kingdom]] is that any doctor who suspects a case of meningococcal meningitis or [[sepsis|septicaemia]] (infection of the blood) should give intravenous antibiotics ([[penicillin|benzylpenicillin]] or [[Cefotaxime]]) and admit the ill person to the hospital.<ref>Health Protection Agency Meningococcus Forum (August 2006). Guidance for public health management of meningococcal disease in the UK. Available online at: http://www.hpa.org.uk/web/HPAwebFile/HPAweb_C/1194947389261</ref> This means that laboratory tests may be less likely to confirm the presence of ''Neisseria meningitidis'' as the antibiotics will dramatically lower the number of bacteria in the body. The UK guidance is based on the idea that the reduced ability to identify the bacteria is outweighed by reduced [[Mortality rate|chance of death]].

[[Septicaemia]] caused by ''Neisseria meningitidis'' has received much less public attention than meningococcal meningitis even though septicaemia has been linked to infant deaths.{{Fact|date=April 2007}} Meningococcal septicaemia typically causes a [[purpuric]] rash that does not turn white when pressed with a glass ("non-blanching") and does not cause the classical symptoms of meningitis. This means the condition may be ignored by those not aware of the significance of the rash. Septicaemia carries an approximate 50% mortality rate over a few hours from initial onset. Many health organizations advise anyone with a non-blanching rash to go to a hospital [[emergency room]] as soon as possible.{{Fact|date=April 2007}} Note that not all cases of a [[purpura]]-like rash are due to meningococcal septicaemia; however, other possible causes need prompt investigation as well (e.g. [[Idiopathic thrombocytopenic purpura|ITP]] a [[platelet]] disorder or [[Henoch-Schönlein purpura]]).

''[[Waterhouse-Friderichsen syndrome]]'' is a massive, usually bilateral, hemorrhage into the adrenal glands caused by [[Wiktionary:fulminant|fulminant]] meningococcemia.


== Virulence ==

Lipooligosaccharide (LOS) is a component of the cell wall of ''N. meningitidis'' which acts as an [[endotoxin]]. Other virulence factors include a [[polysaccharide capsule]] which prevents host [[phagocytosis]] and aids in evasion of the host immune response; and [[fimbriae]] which mediate attachment of the bacterium to the epithelial cells of the [[nasopharynx]].

==Diagnosis==
A [[Cerebrospinal fluid|CSF]] specimen is sent to the laboratory immediately for identification of the organism. Diagnosis relies on culturing the organism on a [[chocolate agar]] plate. Further testing to differentiate the species includes testing for [[oxidase]] (all ''Neisseria'' show a positive reaction) and the [[carbohydrates]] [[maltose]], [[sucrose]], and [[glucose]] test in which ''N. meningitidis'' will oxidize (that is, utilize) the glucose and maltose. Serology determines the group of the isolated organism.

If the organism reaches the circulation, then [[blood cultures]] should be drawn and processed accordingly.

Quintain NS and RMIT University have developed a rapid diagnostic test for meningococcal disease, which will ultimately provide results in under 15 minutes.

Clinical tests that are used currently for the diagnosis of meningococcal disease take between 2 and 48 hours and often rely on the culturing of bacteria from either blood or cerebrospinal fluid (CSF) samples. As the disease has a fatality risk approaching 15% within 12 hours of infection, early diagnosis and antibiotic treatment is crucial.

Quintain is working with Melbourne-based company Charlwood Design, to produce a prototype clinical device that will incorporate a mechanism for safe sample handling and delivery. It is expected that the diagnostic test will be available within 2-3 years, with the nanoparticulate gold diagnostic platform adapted for a range of other clinically important diseases shortly thereafter.

==Vaccines==
There are currently two vaccines available in the US to prevent meningococcal disease. '''[[Menactra]]''' is licensed for use in people aged 11 to 55, while '''[[Menomune]]''' is used for people outside of this age group and for travellers.

''Neisseria meningitidis'' has 13 clinically significant [[serogroup]]s. These are classified according to the antigenic structure of their polysaccharide capsule. Five serogroups, A, B, C, Y and W135 are responsible for virtually all cases of the disease in humans. There is currently no effective vaccine for serogroup B, although a putative vaccine is currently undergoing clinical trials in New Zealand.
*[[Polysaccharide vaccine]]s
*[[Conjugate vaccine]]s

The two quadrivalent (i.e., targeting serogroups A, C, W-135 and Y) meningococcal vaccines available in the US are MCV-4 (a conjugate vaccine '''[[Menactra]]''' manufactured by [[Sanofi Pasteur]] introduced in January 2005) and MPSV-4 (a polysaccharide vaccine marketed as '''[[Menomune]]''', also by [[Sanofi Pasteur]]).

[[Menomune]] has a number of problems. The duration of action is short (3 years or less in children aged under 5),<ref>{{cite journal | author=Reingold AL, Broome CV, Hightower AW, ''et al.'' | title=Age-specific differences in duration of clinical protection after vaccination with meningococcal polysaccharide A vaccine | journal=Lancet | year=1985 | volume=2 | issue=8447 | pages=114–18 | pmid=2862316 | doi=10.1016/S0140-6736(85)90224-7 }}</ref><ref>{{cite journal | author=Lepow ML, Goldschneider I, Gold R, Randolph M, Gotschlich EC. | title=Persistence of antibody following immunization of children with groups A and C meningococcal polysaccharide vaccines | journal=Pediatrics | year=1977 | volume=60 | pages=673–80 | pmid=411104 }}</ref> because it does not generate [[memory T-cell]]s. Attempting to overcome this problem by repeated immunisation results in a diminished, not increased antibody response, so boosters are not indicated with this vaccine.<ref>{{cite journal | author=Borrow R, Joseh H, Andrews N, ''et al.'' | title=Reduced antibody response to revaccination with meningococcal serogroup A polysaccharide vaccine in adults | journal=Vaccine | year=2000 | volume=19 | issue=9&ndash;10 | pages=1129–32 | pmid=11137248 | doi=10.1016/S0264-410X(00)00317-0 }}</ref><ref>{{cite journal | author=MacLennan J, Obaro S, Deeks J, ''et al.'' | title=Immune response to revaccination with meningococcal A and C polysaccharides in Gambian children following repeated immunization during early childhood | journal=Vaccine | year=1999 | volume=17 | issue=23&ndash;24 | pages=3086–93 | pmid=10462244 | doi=10.1016/S0264-410X(99)00139-5 }}</ref> In common with all polysaccharide vaccines, [[Menomune]] does not produce mucosal immunity, so people can still become colonised with virulent strains of meningococcus, and no [[herd immunity]] develops.<ref>{{cite journal | author=Hassan-King MK, Wall RA, Greenwood BM. | title=Meningococcal carriage, meningococcal disease and vaccination | journal=J Infect | year=1988 | volume=16 | issue=1 | pages=55–9 | pmid=3130424 | doi=10.1016/S0163-4453(88)96117-8 }}</ref><ref>{{cite journal | author=Moore PS, Harrison LH, Telzak EE, Ajello GW, Broome CV. | title=Group A meningococcal carriage in travelers returning from Saudi Arabia | journal=J Am Med Assoc | year=1988 | volume=260 | pages=2686–89 | pmid=3184335 | doi=10.1001/jama.260.18.2686 }}</ref> For this reason, [[Menomune]] is eminently suitable for travellers requiring only short term protection, but has no place in national public health programmes.

[[Menactra]] contains the same antigens as [[Menomune]], but the antigens are conjugated to diphtheria toxoid. It is hoped that this formulation will overcome the limitations of [[Menomune]]. [[Menactra]] is currently licensed only for use in people aged 11 to 55, therefore people outside of this age group can only be offered [[Menomune]].

A study published in March 2006 comparing the two vaccines found that 76% of subjects still had passive protection three years after receiving MCV-4 (63% protective compared with controls), but only 49% has passive protection after receiving MSPV-4 (31% protective compared with controls).<ref name=Vu_2006>{{cite journal |author=Vu D, Welsch J, Zuno-Mitchell P, Dela Cruz J, Granoff D |title=Antibody persistence 3 years after immunization of adolescents with quadrivalent meningococcal conjugate vaccine |journal=J Infect Dis |volume=193 |issue=6 |pages=821–8 |year=2006 |pmid=16479517 |doi=10.1086/500512}}</ref> This has implications for the timing of recommendations for when meningococcal vaccines should be given, because there is currently no evidence that any of the current vaccines offer continued protection beyond three years.

==References==
{{reflist}}

==External links==
*[http://www.episcangis.org EpiscanGIS Online Monitoring of Invasive Meningococcal Disease] in Germany
*[http://www.meningitis.org/sect2/subsect0 Main symptoms of meningitis and septicaemia] from Meningitis
*[http://www.quintain.com.au/technologies/technologies/nanoparticle-diagnostics.html] Quintain NS Diagnostics from NanoVic
Research Foundation

[[Category:Proteobacteria]]

[[cs:Neisseria meningitidis]]
[[de:Meningokokken]]
[[es:Neisseria meningitidis]]
[[fr:Neisseria meningitidis]]
[[id:Meningokokus]]
[[it:Neisseria meningitidis]]
[[nl:Meningokok]]
[[ja:髄膜炎菌]]
[[pl:Dwoinka zapalenia opon mózgowo-rdzeniowych]]
[[pt:Meningococo]]
[[fi:Meningokokki]]
[[vi:Meningococcus]]
[[tr:Neisseria meningitidis]]
[[zh:腦膜炎雙球菌]]

Revision as of 08:03, 13 October 2008

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