Norwalk viruses. Coloured transmission electron micrograph (TEM) of a section through several Norwalk virus particles. The Norwalk virus was originally isolated from an outbreak of illness in Norwalk, Connecticut, USA, in 1968. Characteristic of Norwalk viruses is their ill-defined hairy" surface. Symptoms of infection include diarrhoea and outbreaks of vomiting. The Norwalk virus is believed to be similar to the caliciviruses, which are also implicated in human gastroenteritis and have been found in the faeces of children with diarrhoea. Magnification: x205,000 when printed 10cm wide."