Hepatitis viruses: changing patterns of human disease.

Viral hepatitis is a disease of antiquity, but evidence for more than one etiologic agent has been recognized only since the 1940s, when two viruses (hepatitis A virus and hepatitis B virus) were thought to account for all disease. In the past 20 years, three additional hepatitis agents (hepatitis C virus, hepatitis D virus, and hepatitis E virus) have been discovered, and there is evidence for at least one additional virus. Each of the five recognized hepatitis viruses belongs to a different virus family, and each has a unique epidemiology. The medical impact of these viruses on society has been strongly influenced by changes in human ecology. This has resulted in some cases in diminished disease and in others in increases in the incidence of disease.

病毒性肝炎是一种古老的疾病，但学界直至20世纪40年代才证实存在不止一种致病病原体；彼时人们认为，所有病毒性肝炎均由甲型肝炎病毒（hepatitis A virus）与乙型肝炎病毒（hepatitis B virus）这两种病毒引发。
在过去20年间，研究人员又陆续发现了另外三种肝炎病原体：丙型肝炎病毒（hepatitis C virus）、丁型肝炎病毒（hepatitis D virus）及戊型肝炎病毒（hepatitis E virus），同时已有证据表明至少还存在另一种肝炎相关病毒。
目前已被正式确认的五种肝炎病毒分属不同的病毒科，且各自具备独特的流行病学特征。
上述病毒对社会造成的医学影响，受人类生态环境变化的显著影响：在部分场景中，这类疾病的发病负担有所缩减；而在另一些场景中，其发病率反而出现了上升。