An attempt at an epidemiological explanation - Epib.nl

Introductionclone with an new phenotype (B:2b:P1.2) was responsible for the 1966 epidemic inthe Netherlands." 62 Meningococci of the phenotype B:1S:P1.7,16 caused a protractedepidemic in Norway tbat started in 1974." 63 This pbenotype was the main representativeof a complex of meningococcal clones (ET-S complex), which has slowly spreadto the south of Europe, and further to the Americas, but epidemics or local outbreaksin other parts of the world, due to clones of the ET-5 complex, were often ofother phenotypes, e.g. B:4:Pl.lS in Cuba and B:1S:P1.3 in Chile."Natural immunityInfants younger than 6 months of age are relatively protected against MD, due topassive immunization by transplacentally transferred maternal antibodies" As thelevel of these antibodies decreases, the host will become susceptible to variousmeningococci, and natural immunity has to be built up." Immunity is thought to beacquired by (repeated) carriage of both encapsulated and nonencapsulated meningococci,as well as nonvirulent Neisseria species, like N. lactarnica. M Both specific andcross-reactive antibodies are induced by the various surface components of thesemeningococci. During a life-time many different meningococci will be acquired,resulting in broad immunity against various meningococcal antigens.Age-distributionMD is predominantly a disease of childhood, and the chance of its occurrence isinversely related to the level of specific antibodies in the bost." The peak incidence isamong children from 6 months to 5 years of age who are immunoiogically naive, andanother small peak is noted among teenagers." 0560 The latter peak might be due to acbange in life-style or biological changes during puberty."The age-distribution differs among the various serogroups." S3 os Meningococci ofserogroup C, and to a lesser extent of serogroup A, are found relatively more oftenamong older patients, as compared to those of serogroup B.The emergence of a new meningococcal phenotype in a certain geographical areaoften results in an increase in the number of c.:1Ses in the older age-categories, whichare then relatively over-represented. 656869Pathogenesis and clinical syndromesA review of current knowledge of the pathogenesis of bacterial meningitis has beenprovided recently by Quagliarello and Scheld.' The pili are thought to play a mainrole in the adherence on cells present in the nasopharyngeal mucosa and the bloodbrainbarrier. The capsule enables the meningococcus to evade the host defensemechanisms and to survive in the bloodstream of the host. The LOS (endotoxin) isconsidered as an important mediator in the inflammatory process in the CSF and inthe development of septic shock.' \0 Meningococci are capable of releasing parts oftheir outer membrane ("blebs"), which contain high concentrations of LOS." LOSinduces a cytokine cascade (turnor necrosis factor, interleukin-l, interleukin-6), which9