Norwalk virus or Noravirus. Artwork showing the caspsid structure of a Norwalk virus particle. Single positive-sense RNA genome (ribonucleic acid) being encapsulated in a ichosaedral protein capsid. In Red pentons and in dark hexons. The virus causes vomiting, diarrhoea and stomach pains and is transmitted by contaminated food and water. The capsid appears hexagonal-spherical and has icosahedral symmetry with a diameter of 35-39 nm.