Neisseria meningitidis, also simply known as meningococcus, is a heterotophic gram-negative diplococcal bacterium best known for its role in meningitis. It only infects humans; there is no animal reservoir. It is the only form of bacterial meningitis known to cause epidemics. There are many strains of meningococcus; the most clinically important are A, B, C, X, Y and W135: , A - occurs most often in sub-sahara Africa and vaccination...