serotypes
Summary
Serotypes are variants within a bacterial or viral species distinguished by the antigens on their surface, defined by their reaction with specific antisera. Serotype diversity explains repeat infections and shapes vaccine design.
Detail
Because immunity is often serotype-specific, a person can be infected repeatedly by different serotypes of the same organism. Streptococcus pneumoniae has more than ninety capsular serotypes; the conjugate vaccine covers a selected subset and its use has driven serotype replacement, in which non-vaccine serotypes rise in prevalence. Neisseria meningitidis serogroups A, B, C, W, and Y are covered by different vaccines, with group B requiring a protein-based rather than polysaccharide vaccine because its capsule mimics human neural sialic acid. Salmonella is classified into over two thousand serovars by the Kauffmann-White scheme using O, H, and Vi antigens. E. coli serotypes such as O157:H7 identify enterohaemorrhagic strains producing Shiga toxin and causing haemolytic uraemic syndrome. Human papillomavirus types 16 and 18 cause most cervical cancer while 6 and 11 cause genital warts, all covered by the nine-valent vaccine. Dengue's four serotypes underlie antibody-dependent enhancement, in which prior infection with one serotype worsens disease on subsequent infection with another.
Sources
- Levinson Medical Microbiology and Immunology
- Janeway's Immunobiology
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