A picornavirus is a virus belonging to the family Picornaviridae, a family of viruses in the order Picornavirales. Vertebrates, including humans, serve as natural hosts. Picornaviruses are nonenveloped viruses that represent a large family of small, cytoplasmic, plus-strand RNA (~7.5kb) viruses with a 30-nm icosahedral capsid. Its genome does not have a lipid membrane. Picornaviruses are found in mammals and birds. There are currently 80 species in this family, divided among 35 genera. Notable examples are Enterovirus (including Rhinovirus and Poliovirus), Aphthovirus, Cardiovirus, and Hepatovirus genera. The viruses in this family can cause a range of diseases including paralysis, meningitis, hepatitis and poliomyelitis. Picornaviruses are in Baltimore IV class. Their genome single-stranded (+) sense RNA is what functions as mRNA after entry into the cell and all viral mRNA synthesized is of genome polarity. The mRNA encodes RNA dependent RNA polymerase. This polymerase makes complementary minus strands of RNA, then uses them as templates to make more plus strands. So, an overview of the steps in picornavirus replication are in order: attachment, entry, translation, transcription/genome replication (one and the same process), assembly and exit.