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The Hepatitis [[virus]] (HAV) is a [[Picornavirus]]; it is [[Viral envelope|non-enveloped]] and contains a [[Positive-sense ssRNA virus|single-stranded RNA]] packaged in a protein [[capsid|shell]].<ref name="pmid17328982">{{cite journal |author=Cristina J, Costa-Mattioli M |title=Genetic variability and molecular evolution of hepatitis A virus |journal=Virus Res. |volume=127 |issue=2 |pages=151–7 |year=2007 |month=August |pmid=17328982 |doi=10.1016/j.virusres.2007.01.005 |url= |issn=}}</ref> There is only one [[serovar|serotype]] of the virus, but multiple genotypes exist.<ref name="pmid14645901">{{cite journal |author=Costa-Mattioli M, Di Napoli A, Ferré V, Billaudel S, Perez-Bercoff R, Cristina J |title=Genetic variability of hepatitis A virus |journal=J. Gen. Virol. |volume=84 |issue=Pt 12 |pages=3191–201 |year=2003 |month=December |pmid=14645901 |doi= 10.1099/vir.0.19532-0|url=http://vir.sgmjournals.org/cgi/pmidlookup?view=long&pmid=14645901 |issn=}}</ref>
[[Codon]] use within the genome is biased and unusually distinct from its host. It also has a poor internal ribosome entry site<ref name="Whetter1994">Whetter LE, Day SP, Elroystein O, Brown EA, Lemon SM (1994) Low efficiency of the 5' nontranslated region of hepatitis A virus RNA in directing cap-independent translation in permissive monkey kidney cells. J Virol 68: 5253–5263 </ref> Within the in the HAV capsid-coding region there is a specific region with highly conserved clusters of rare codons has been related to the low antigenic variability. Mutations in these clusters are negatively selected even in the presence of immune pressure.<ref name="Aragones2008">Aragones L, Bosch A, Pinto RM (2008) Hepatitis A virus mutant spectra under the selective pressure of monoclonal antibodies: Codon usage constraints limit capsid variability. J Virol 82: 1688–1700</ref>
Following ingestion, HAV enters the bloodstream through the epithelium of the [[oropharynx]] or intestine.<ref name="Murray, P. r. 2005">Murray, P. R., Rosenthal, K. S. & Pfaller, M. A. (2005) Medical Microbiology 5th ed., Elsevier Mosby.</ref> The blood carries the virus to its target, the liver, and multiplies within [[hepatocytes]] and [[Kupffer cells]] (liver macrophages). [[Virions]] are secreted into the [[bile]] and released in stool. HAV is excreted in large quantities approximately 11 days prior to appearance of symptoms or anti-HAV [[IgM]] [[antibodies]] in the blood. The [[incubation period]] is 15–50 days and mortality is less than 0.5%.
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