Neisseria meningitidis

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Neisseria meningitidis

Scientific classification

Kingdom:	Bacteria
Phylum:	Proteobacteria
Class:	Beta Proteobacteria
Order:	Neisseriales
Family:	Neisseriaceae
Genus:	Neisseria
Species:	N. meningitidis

Binomial name

Neisseria meningitidis
Albrecht & Ghon 1901

Neisseria meningitidis, also simply known as meningococcus is a gram-negative bacterium best known for its role in meningitis.^[1] It only infects humans; there is no animal reservoir. It is the only form of bacterial meningitis to cause epidemics.

1 Clinical Presentations
2 Strains
3 Vaccines
4 See also
5 References
6 External links

[edit] Clinical Presentations

Whilst a non-specific illness initially, this can rapidly progress through fever, headache and neck stiffness to coma and death. The mortality is approximate 10% of cases. Suspicion of meningitis is a medical emergency and immediate medical assessment is recommended.

Septicaemia ("blood poisoning") has received much less public attention, but has been linked to infant deaths. Whilst there may be an absence of the classical meningitis symptoms, the presence of a non-blanchable purpuric rash is easily ignored by those not aware of its significance. Septicaemia carries an approximate 50% mortality rate over a few hours from initial onset. Anyone developing a rash that does not turn white ("non-blanching") if pressed with a glass is advised to attend a hospital casualty department as soon as possible.^[2]

Waterhouse-Friderichsen syndrome is a massive, usually bilateral, hemorrhage into the adrenal glands caused by fulminant meningococcemia.

UK policy is that any General Practitioner doctor seeing a suspected case of meningococcus meningitis or septicaemia should give intravenous antibiotics (benzylpenicillin) whilst hospital admission is sought. The possible reduction in subsequent microbiological confirmation of infection, due to starting treatment before testing, is offset by the reduced mortality.

Not all cases of a purpura-like rash are due to septicaemia, but the other causes also need prompt investigation (e.g. ITP a platelet disorder or Henoch-Schönlein purpura a vasculitis).

Those with impaired immunity may be at particular risk of meningococcus, e.g. those with nephrotic syndrome or splenectomy. In asplenia (removed or non-functioning spleen), vaccination is performed according to protocols.

[edit] Strains

There are many strains of meningococcus, clinically the most important are A, B, C, 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.
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.
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, X, and Z.

[edit] 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 serogroups. 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.

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 duraction of action is short (3 years or less in children aged under 5),^[3]^[4] because it does not generate memory T-cells. Attempting to overcome this problem by repeated immunisation results in a diminished, not increased antibody response, so boosters are not indicated with this vaccine.^[5]^[6] 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.^[7]^[8] 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).^[9] 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.

[edit] See also

[edit] References

^ Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology, 4th ed., McGraw Hill, 329–333. ISBN 0838585299.
^ Meningitis. NHS Direct (15/03/2006). Retrieved on 2006-09-19.
^ Reingold AL, Broome CV, Hightower AW, et al. (1985). "Age-specific differences in duration of clinical protection after vaccination with meningococcal polysaccharide A vaccine". Lancet 2 (8447): 114–18. PMID 2862316.
^ Lepow ML, Goldschneider I, Gold R, Randolph M, Gotschlich EC. (1977). "Persistence of antibody following immunization of children with groups A and C meningococcal polysaccharide vaccines". Pediatrics 60: 673–80. PMID 411104.
^ Borrow R, Joseh H, Andrews N, et al. (2000). "Reduced antibody response to revaccination with meningococcal serogroup A polysaccharide vaccine in adults". Vaccine 19 (9–10): 1129–32. PMID 11137248.
^ MacLennan J, Obaro S, Deeks J, et al. (1999). "Immune response to revaccination with meningococcal A and C polysaccharides in Gambian children following repeated immunization during early childhood". Vaccine 17 (23–24): 3086–93. PMID 10462244.
^ Hassan-King MK, Wall RA, Greenwood BM. (1988). "Meningococcal carriage, meningococcal disease and vaccination". J Infect 16 (1): 55–9. PMID 3130424.
^ Moore PS, Harrison LH, Telzak EE, Ajello GW, Broome CV. (1988). "Group A meningococcal carriage in travelers returning from Saudi Arabia". J Am Med Assoc 260: 2686–89. PMID 3184335.
^ Vu D, Welsch J, Zuno-Mitchell P, Dela Cruz J, Granoff D (2006). "Antibody persistence 3 years after immunization of adolescents with quadrivalent meningococcal conjugate vaccine". J Infect Dis 193 (6): 821-8. PMID 16479517.