Illustration of a rotavirus. So called because of the wheel-like appearance of the capsid (protein shell), with its inner hub-like core and spokes radiating out. All viruses consist simply of an inner core of nucleic acid surrounded by one or more protective protein shells. Rotaviruses are the commonest cause of gastro-enteritis in young children and among the elderly. They are a cause of traveller's diarrhoea. Resistant to stomach acid, they infect the lining of the small intes- tine and impair the absorptive function of cells. They are easily transmitted from hand to mouth. By age 6, most children have antibodies and some resistance to the common rotaviruses.