Common cold virus. Computer graphic image showing a rhinovirus particle, the most important cause of the common cold and the upper respiratory tract infections. Rhinoviruses belong to the Picornaviridae family which comprises small (about 30 nanometres) RNA viruses with a naked (without external envelope) capsid structure. Rhinoviruses may be transmitted by two mechanisms: aerosols and direct contact. The clinical symptoms of infections caused by rhinoviruses include sneezing, nasal obstruction, mild sore throat and headache.