Neisseria meningitidis
| "Neisseria mengitidis" | |
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| Photomicrograph of N. meningitidis | |
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| Species: | N. meningitidis
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| Binomial name | |
| Neisseria meningitidis Albrecht & Ghon 1901
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Neisseria meningitidis is a heterotrophic gram-negative diplococcal bacterium best known for its role in meningitis[1] and other forms of meningococcal disease such as meningococcemia. N. meningitidis is a major cause of morbidity and mortality in childhood in industrialized countries and is responsible for epidemics in Africa and in Asia.
Anton Weichselbaum in 1887 was first reported the disease from patients infected with meningococci [2].
Meningococci only infect humans and have never been isolated from animals because the bacterium cannot get iron other than human source (transferrin and lactoferrin).[3]
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 epidemics.
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, it can rapidly progress from fever, headache and neck stiffness to coma and death. Death occurs in approximately 10% of cases.[4] 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 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 septicaemia (infection of the blood) should give intravenous antibiotics (benzylpenicillin or Cefotaxime) and admit the ill person to the hospital.[5] 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 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. [6] Meningococcal septicaemia typically causes a purpuric rash that does not lose its colour 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.[citation needed] 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. ITP a platelet disorder or Henoch-Schönlein purpura).
Waterhouse-Friderichsen syndrome is a massive, usually bilateral, hemorrhage into the adrenal glands caused by fulminant meningococcemia.
Virulence
Lipopolysaccharide (LPS) 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 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.
References
- ^ Ryan KJ, Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. pp. 329–333. ISBN 0838585299.
{{cite book}}:|author=has generic name (help) - ^ van Deuren, M., Brandtzaeg, P., and van der Meer, J .W. .M. (2000). Update on meningoccal disease with emphasis on pathogenesis and clinical management. Clinical Microbiological Reviews. 13, 144-166
- ^ Meningococcal Disease (2001) Humana Press, Andrew J. Pollard and Martin C.J. Maiden
- ^ Meningococcal Disease (2001) Humana Press, Andrew J. Pollard and Martin C.J. Maiden
- ^ 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
- ^ Meningococcal Vaccines (2001) Humana Press, Andrew J. Pollard and Martin C.J. Maiden