J. Joukje Siebenga, Erwin Duizer and Marion P.G. Koopmans
from: Caliciviruses: Molecular and Cellular Virology (Edited by: Grant S. Hansman, Xi Jason Jiang and Kim Y. Green). Caister Academic Press, U.K. (2010)
Noroviruses are the dominant cause of outbreaks as well as sporadic community cases of viral gastroenteritis in the world. Their very low infectious dose, combined with high levels of shedding and long persistence in the environment make noroviruses extremely infectious. Although generally norovirus related illness is regarded as mild and self-limiting, more severe outcomes are increasingly described among elderly and immuno-compromised patients. The combination of large and difficult to control outbreaks and severe illness in some patients leads to major problems in healthcare settings, such as hospitals and nursing homes. Additionally, some large and diffuse, multi-national and even multi-continent, foodborne-outbreaks have been described for norovirus, affecting up to thousands of people. With structured outbreak surveillance running in a number of regions across the world for the past ten years, it has become clear that the spread of noroviruses is global, although important information from developing countries is missing. At present, norovirus strains belonging to genogroup II genotype 4 (GII.4) are dominant worldwide. In the last ten years, at least three global pandemics involving GII.4 strains of different genetic variants occurred. Although a straightforward culturing method remains lacking for noroviruses, important progress has been made in immunological studies using virus-like particles. Thus it has been shown that the subsequent genetic variants of GII.4 are antigenically distinct, and that the GII.4 noroviruses evolved and continue to do so by a process known as epochal evolution, in which periods of genetic stasis are interrupted by rapid accumulation of mutations and the subsequent emergence of novel genetic variants. In norovirus evolution, this process is directed by population or herd immunity read more ...