Thickening the Alphabet Soup: The Emergence of Hepatitis E

William F. Balistreri, MD


April 25, 2013

In This Article

The Hepatitis Alphabet

First came the discovery of the hepatitis A virus (HAV), and then came the hepatitis B virus (HBV). Hence, every other form of viral-induced liver injury was called "non-A, non-B hepatitis" -- a cumbersome term that clearly encompassed a diverse group of specific infectious agents.

The spectrum narrowed greatly with the discovery of the hepatitis C virus (HCV) and hepatitis D (delta) virus (HDV). However, screening for the known forms was still often negative, giving rise to the irksome (to me) term "non-A, non-B, non-C, non-D" hepatitis!

It was somewhat of a relief to hear of the emergence of a validated fifth known form of human hepatitis virus -- hepatitis E virus (HEV). In fact, HEV is probably the most common cause of acute hepatitis, with seroprevalence data suggesting that one third of the world's population has been infected with HEV.[1]


HEV, the sole member of the genus Hepevirus in the family Hepeviridae, is a small nonenveloped RNA virus. HEV exhibits aspectrum of at least 4 known genotypes; genotypes 1 and 2 are human viruses, and genotypes 3 and 4 are swine viruses that are common in domestic and wild pigs.[2,3,4,5]

The discovery of HEV followed visualization of HEV in fecal samples by immune electron microscopy, isolation of the viral genome from bile samples of experimentally infected macaques, and sequencing of HEV RNA. This allowed development of diagnostic assays for anti-HEV.[6,7]