Astrovirus particles, illustration. Astroviruses are small viruses, about 28 nanometres in diameter, and first identified in 1975 using electron microscopy. They contain a single-stranded ribonucleic acid (RNA) genome within a non-enveloped icosahedral (20-sided) outer protein coat (capsid, blue). Astroviruses cause a form of gastroenteritis in humans, particularly children, with symptoms such as diarrhoea, nausea, vomiting, fever, and abdominal pain. However, they have been poorly studied as they do not grow in a culture.