Neisseria meningitidis

Neisseria meningitidis is a heterotrophic gram-negative diplococcal bacterium best known for its role in meningitis and other forms of meningococcal disease such as meningococcemia. It is a major cause of morbidity and mortality during childhood in industrialized countries and is responsible for epidemics in Africa and in Asia.

In the US there are approximately 2500 to 3500 cases of N. meningitides infections. Children under 5 are at a higher risk as well as people in the sub-Saharan Africa. The disease was first discovered in patients with meningococci in 1887 by Anton Weichselbaum.

It can only infect humans and it has never been isolated from animals because the bacterium cannot get iron other than from a human sources. It exists as normal flora in the nasopharynx of up to 5-15% of adults. It can cause the only epidemically capable form of bacterial meningitis.

Meningococcus is spread through saliva and other respiratory secretions during activities like coughing, kissing, and chewing on toys. Symptoms include fatigue, fever, headache, neck stiffness, coma, and even death. These symptoms can be easily confused with meningitis due to other organisms like Hemophilus influenze and Streptococcus pneumoniae. In 10% of cases Death occurs. Anyone with impaired immunity may be at particular risk.

Suspicion of meningitis is a medical emergency and immediate medical assessment is recommended. Any suspicious case should be admitted to the hospital. Septicaemia has received less attention than meningococcal meningitis even though it has been linked to infant deaths. The condition may be ignored due to those not aware of the significance of the rash. Septicaemia has approximately a 50% mortality rate over a few hours from initial onset. A hypervirulent strain was discovered in China although it is yet to be determined.

N. meningitides is an intracellular human-specific pathogen responsible for septicemia and meningitis. It exploits host cell signaling pathways to promote its uptake by host cells. It has neither a type III secretion system nor a type IV secretion system.
Through isolation of sterile body fluid diagnosis of N. meningitides is achieved. Diagnosis relies on culturing the organism on a chocolate agar plate. Quintain NS and RMIT University have created a rapid diagnostic test for meningococcal disease. Polymerase chain reaction tests can be used to identify the organism even after antibiotics have begun to reduce the infection.

Anyone around an infected person 7 days before the onset of symptom should be checked and possibly be on chemoprophylaxis. There are two vaccines available in the US, Meningococcal conjugate vaccine and meningococcal polysaccharide vaccine.