Norovirus (from J Virol. 82:2079-2088 (2008))

P.G. Wodehouse described his “Blandings Castle” short stories as “the short snorts between the solid orgies”. I usually go for at least one of the solid orgies per week,1 but it’s spring break and I’m hanging out with my kids for the next while.2 So this week and likely next, we’re looking at short snorts.

RNA viruses in general have very high mutation rates compared to most of the things (viral or otherwise) with a DNA genome. This is a double-edged sword:3 A high mutation rate lets the virus exist as a quasi-species that includes a vast number of variants within it, and offers the capability for rapid evolution; but on the other hand, RNA viruses generally exist right at the edge of catastrophic mutation rates that would lead to the entire population collapsing.

This study of noroviruses4 suggests that the most successful (in terms of repeated pandemics) virus strains have a higher mutation rate than the less-successful strains. It’s a correlation rather than definitively a cause, but an interesting correlation.

It has been hypothesized that viruses are fitter if they are able to produce a more robust (diverse) population … In the current study we examined whether there was a link between epidemiological fitness, as defined by their incidence, and the rate and accuracy of viral replication…. Our results are consistent with mutation rates for the poliovirus RdRp and retrovirus reverse transcriptases, which range between 10-3 to 10-5. The more prevalent GII.4 strains had a 5 to 36-fold higher mutation rate compared to the less frequently detected GII.b/GII.3 and GII.7 strains, as determined by in vitro enzyme assays. 4

(My emphasis) There were several other interesting aspects to this study, including the suggestion that the pandemic noroviruses are undergoing antigenic drift in a similar way to influenza viruses.

For comparison, most researchers5 find that influenza virus mutation rates are at the upper (lower mutation rate) range for RNA viruses.

Virus polymerase error rates
RNA virus mutation rates 6

To forestall another question, rate of evolution and rate of mutation are not the same thing:

Mutation rate and rate of evolution cannot be directly compared as they are indirectly related due to the increased complexity of evolution in vivo.4

  1. On this blog, I mean[]
  2. We’re visiting Pittsburgh on the weekend, and hopefully catching Chicago museums, zoos, and aquaria next week, and meanwhile playing baseball and such in the back yard[]
  3. What a dumb metaphor this is, by the way. Lots of swords had double edges, and people weren’t cutting themselves left and right with them. “A sword with an edged hilt” would be a better comparison, if such a thing existed.[]
  4. Bull, R., Eden, J., Rawlinson, W., & White, P. (2010). Rapid Evolution of Pandemic Noroviruses of the GII.4 Lineage PLoS Pathogens, 6 (3) DOI: 10.1371/journal.ppat.1000831[][][]
  5. There are a couple of outliers in either direction[]
  6. CASTRO, C., ARNOLD, J., & CAMERON, C. (2005). Incorporation fidelity of the viral RNA-dependent RNA polymerase: a kinetic, thermodynamic and structural perspective Virus Research, 107 (2), 141-149 DOI: 10.1016/j.virusres.2004.11.004[]