About 90% of children do not have symptoms. The time between infection and symptoms, in those who develop them, is between 2 and 6 weeks with an average of 28 days. The risk for symptomatic infection is directly related to age, with more than 80% of adults having symptoms compatible with acute viral hepatitis and the majority of children having either asymptomatic or unrecognized infections. Symptoms usually last less than 2 months, although some people can be ill for as long as 6 months:   Joint pains, red cell aplasia, pancreatitis and generalized lymphadenopathy are the possible extrahepatic manifestations. Kidney failure and pericarditis are very uncommon. If they occur, they show an acute onset and disappear upon resolution of the disease. "Hepatovirus A" is a species of virus in the order "Picornavirales" in the family "Picornaviridae" and is the type species of the genus "Hepatovirus". Humans and vertebrates serve as natural hosts. A total of nine members of "Hepatovirus" are recognized. These species infect bats, rodents, hedgehogs, and shrews. Phylogenetic analysis suggests a rodent origin for Hepatitis A. A member virus of "Hepatovirus B" (Phopivirus) has been isolated from a seal. This virus shared a common ancestor with "Hepatovirus A" about 1800 years ago. Another hepatovirus - Marmota himalayana hepatovirus - has been isolated from the woodchuck "Marmota himalayana". This virus appears to have had a common ancestor with the primate-infecting species around 1000 years ago. One serotype and seven different genetic groups (four human and three simian) have been described. The human genotypes are numbered I–III. Six subtypes have been described (IA, IB, IIA, IIB, IIIA, IIIB). The simian genotypes have been numbered IV–VI. A single isolate of genotype VII isolated from a human has also been described. Genotype III has been isolated from both humans and owl monkeys. Most human isolates are of genotype I. Of the type I isolates subtype IA accounts for the majority. The mutation rate in the genome has been estimated to be nucleotide substitutions per site per year. The human strains appear to have diverged from the simian about 3600 years ago.