Picornaviruses

(from Spanish pico, “small quantity,” and RNA, abbreviation for ribonucleic acid), a group of viruses that lack an envelope and contain a single strand of RNA. Picornaviruses replicate in the cytoplasm of bacterial, plant, animal, and human cells. They are the smallest known viruses, reaching a maximum diameter of about 30 nanometers. The most studied picornaviruses are the enteroviruses, which inhabit human and animal intestines. Many picornaviruses, for example, the polio-virus, can attack the central nervous system. Picornaviruses also include the virus that causes foot-and-mouth disease, murine encephalitis virus, rhinoviruses (which cause inflammation of the upper respiratory tract in man and animals), yellow turnip mosaic virus, and bacteriophage f2.