Hepatitis A virus is an unenveloped, single-stranded RNA virus with cubic symmetry and a diameter of 27 nm (Fig 37–1). The virus resists inactivation and is stable at –20°C with low pH. These properties are similar to those of picornaviruses, and hepatitis A virus has now been classified in a separate genus of picornaviruses as a hepatovirus. There is only one serotype of hepatitis A virus. The virus has been successfully cultivated in primary marmoset liver cell cultures and in fetal rhesus monkey kidney cell cultures.