Rotavirus particles, 3D computer illustration based on scanning electron microscopy (SEM) imagery. Each virus particle consists of an RNA (ribonucleic acid) core surrounded by a triple layered capsid. Rotaviruses are probably the most common viruses to infect humans and animals. They are associated with gastroenteritis and diarrhoea - typically infecting the intestines of children aged from 6 months to 3 years. The viruses are spread in faeces.