This acts as an endotoxin and is responsible for septic shock and hemorrhage due to the destruction of red blood cells. Other virulence factors include a polysaccharide capsule which prevents host phagocytosis and aids in evasion of the host immune response. Adhesion is another key virulence strategy to successfully invade host cell. There are several known proteins that are involved in adhesion and invasion, or mediate interactions with specific host cell receptors. These include the Type IV pilin adhesin which mediates attachment of the bacterium to the epithelial cells of the nasopharynx, surface-exposed Opa and Opc proteins which mediate interactions with specific host cell receptors, and NadA which is involved in adhesion.Pathogenic meningococci that have invaded into the bloodstream must be able to survive in the new niche, this is facilitated by acquisition and utilisation of iron (FetA and Hmbr), resisting intracellular oxidative killing by producing catalase and superoxide dismutase and ability to avoid complement mediated killing (fHbp). Meningococci produce an IgA protease, an enzyme that cleaves IgA class antibodies and thus allows the bacteria to evade a subclass of the humoral immune system. A hypervirulent strain was discovered in China. Its impact is yet to be determined. Complement inhibition
Factor H binding protein (fHbp) that is exhibited in N. meningitidis and some commensal species is the main inhibitor of the alternative complement pathway. fHbp protects meningococci from complement-mediated death in human serum experiments, but has also been shown to protect meningococci from antimicrobial peptides in vitro.
Symptoms of meningococcal meningitis are easily confused with those caused by other bacteria, such as Haemophilus influenzae and Streptococcus pneumoniae. Suspicion of meningitis is a medical emergency and immediate medical assessment is recommended. Current guidance in the United Kingdom is that if a case of meningococcal meningitis or septicaemia (infection of the blood) is suspected, intravenous antibiotics should be given and the ill person admitted to the hospital. 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. Meningococcal septicaemia typically causes a purpuric rash, that does not lose its color when pressed with a glass slide ("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.