2. CAUSATIVE AGENT

Vieusseaux first described “cerebrospinal fever” in 1805 when an outbreak swept though Geneva, Switzerland. Reports throughout the 19th century confirmed the episodic, epidemic nature of the disease tending to affect young children and military recruits living in barracks. The causative agent, Neisseria meningitidis (the meningococcus), was identified in 1887 when Weichselbaum reported finding a new organism in the cerebrospinal fluid of six post-mortem cases during an epidemic. He called the organism “diplococcus intracellular meningitis”, to distinguish it from the intracellular diplococcus gonorrhoea identified by Neisser in 1879.

Meningococci are classified according to the characteristics of their polysaccharide capsule. Thirteen serogroups of N. meningitidis have been identified and five (A, B, C, W135 and Y) are recognized to cause epidemics. The pathogenicity, immunogenicity, and epidemic capabilities differ according to the serogroup. The identification of the serogroup is important for surveillance purposes and decisions about public health responses.