Classification and Taxonomy

Picorna viridae is divided into five different genera: Aphtovirus, Cardiovirus, Enterovirus, Hepatovirus, and Rhinovirus (for more information see the  Tulane University Picorna Virus Page )Three of them, Enterovirus, Rhinovirus, and Hepatovirus, include human pathogens. See  Associated Viruses and Diseases, for a list of human viruses and diseases associated with each genus.

ssRNA (infectious), positive sense, linear, nonsegmented, poly-A tail, protein covalently linked at 5' end : VPg .


icosahedral, naked, 32 capsomers made up of four polypeptides : VP1,VP2,VP3, and VP4 (12 pentons with five copies of VP1 each, 20 hexons consisting of VP2 and VP3, VP4 underneath surface of the capsid face) 7.5-8.5kb, 25-30 nm in diameter ( the smallest RNA virus), appears smooth and round under electron microscopy.


Replication takes place in the cytoplasm. The positive sense single stranded RNA functions as mRNA and therefore does not require transcriptase in the virion.  Following adsorption, penetration, and uncoating VPg is removed by enzymes and the mRNA is translated into a polyprotein; it is then cleaved into P1,P2, and P3 which act as intermediates.  They are further cleaved to eventually form structural and nonstructural proteins as well as an RNA dependent RNA polymerase  (VP4,VP2,VP3,VP1,2A,2B,2C,3A,VPg,3C, and 3D).  Synthesis of the complementary strand uses the VPg protein as a primer and is initiated at the 3' end.  This strand acts as a template for the virion RNA. (see diagram below)

1996, Courtesy of Dr. Alan Cann / University of Leicester