Norovirus
Valerie Cortez, Shannon Banner, Shirleen Soh
Virus characteristics
- Non-enveloped, Group IV +ssRNA virus
- 7 genogroups (60% divergence in capsid between genogroups, 20-30% within genogroup) comprised of 32 genotypes are known to infect humans
- Humans are the only known reservoir
- Where do emergent strains come from?*
Immune response & virus evolution
- Strain-specific, genotype-specific
- Immunity to homologous strain ranges 6 months to 2 years
- Why is the antibody response so short-lived?*
- Strain-specific genetic susceptibility based on histo-blood group antigen expressed on epithelial cells (functional FUT2 gene aka "secretors"), provides attachment factor for virus
- Diversity in HBGAs (carbohydrates) allows virus to explore antigenic space to avoid host immunity, evidenced by faster evolution of capsid domain that binds HBGAs
Challenges
- No good animal model, human studies required for vaccine trials/challenge studies (only in adults)
- Polyvalent vaccine? Updated yearly?*
- Lack of robust cell culture system
- Serology difficult with such antigenically distinct strains, limited sensitivity