Meningococcal Meningitis

Meningococcal meningitis is a relatively common disease in humans, sometimes occurring in large-scale epidemic form, or more often in small clusters - typically associated with close contact of young adult humans with each other (e.g., in army boot-camps or colleges). There are multiple serotypes of the causative organism Neisseria meningitides, which differ in the type of surface capsule they express. Some humans are asymptomatic nasopharyngeal carriers of this organism. While meningitis due to other organisms like Streptococcus pneumoniae and Klebsiella pneumoniae have been reported in chimpanzees, cases of Meningococcal meningitis have apparently not been. However, the asymptomatic carrier state has been reported. Interestingly, meningococci present surface sialic acids in a variety of ways, and this may help them to restrict the immune response. It is possible that changes in the sialic acid-recognizing Siglecs on immune cells that occurred in during human evolution may have made us more susceptible to these pathogens.