Viral hepatitis is liver inflammation caused by infection with a virus.

The following viruses cause most cases of viral hepatitis:

• Hepatitis A virus (HAV)
• Hepatitis B virus (HBV)
• Hepatitis C virus (HCV)
• Hepatitis D virus (HDV)
• Hepatitis E virus (HEV)

A virus that causes hepatitis can be spread from one person to another. Hepatitis B, C, and D viruses are spread when a person comes in contact with blood, semen, or vaginal fluid (including menstrual blood) that is infected with one of these viruses. Hepatitis A and E viruses are spread by contaminated food and water or by coming in direct contact with contaminated stool (feces). Hepatitis E is very rare in the United States. Hepatitis D only occurs along with hepatitis B.

In their early (acute) stages, these viruses are difficult to tell apart. However, several weeks to months after infection occurs, blood tests can show which of the viruses is the cause of hepatitis (with the exception of hepatitis E, for which a blood test is not widely available in the United States).

The following viruses are less common causes of hepatitis and can be diagnosed using blood tests:

• Cytomegalovirus (CMV)
• Epstein-Barr virus (which causes infectious mononucleosis)