Hepatitis A (formerly known as infectious hepatitis and epidemical virus) is an acute infectious disease of the liver caused by the hepatitis A virus (Hep A), an RNA virus, usually spread the fecal-oral route; transmitted person-to-person by ingestion of contaminated food or water or through direct contact with an infectious person. Tens of millions of individuals worldwide are estimated to become infected with Hep A each year. The time between infection and the appearance of the symptoms (the incubation period) is between two and six weeks and the average incubation period is 28 days.