Colorized image from a Transmission electron microscope. It shows norovirus particles.
Noroviruses are single-strand RNA-viruses with a diameter between 35 and 38 nm. Their capsid is icosahedric and shows up as a blurry round structure under the TEM. The genome of the norovirus is about 7.3 to 7.7 kB in size and its genome sequence is very variable. The viruses have high tenacity against chemical and physical influences from their surroundings and can survive in teperatures between -20°C to +60°C.
Norovirus shows, like influenzavirus, an antigene-drift and also a seasonal antigene-shift through genetic recombination between different viral strains. At this time (2012) three human-pathogenic norovirus species are differenciated:
After Infection noroviruses multiply mainly inside the small intestine. After about 1 to 2 days the first symptoms appear. These are acute gastroenteritis that lasts 1 to 3 days, with nausea, vomiting, watery diarrhea, and stomach pain. In some cases there is loss of taste. Other general signs of the illness can be sensation of weakness, muscle pain, headache, cough, subfebrile temperature. Normally the illness heals completely and without longterm consequences after this time.
The general course of the illness is normally rather mild. Only in special cases admission to a hospital is necessary. Very young or old patients, or those with a weakend immune system can have bad cases that can rarely end in death, especially if the dehydration that is caused by the illness isn't treated adequately.
At this time (2012 in Germany) there is no vaccine for norovirus. A vaccination with recombined virus like particles (VLPs) is being tested clinically. The oral or intranasal delivery of these VLPs can induce a specific immune response, but this doesn't prevent infection, but leads to a milder course of the illness. It is still inclear, whether it also provides protection against new variants of the virus. This problem is also the same as with influenza virus vaccinations.
(Source of picture: CDC/ Charles D. Humphrey, PhD)
Norovirus (TEM, colorized) 2