Transmission electron micrograph (TEM) revealed numerous hepatitis virions, of an unknown strain of the organism. In the United States, viral hepatitis is an important public health problem because it causes serious illness, it affects millions, and it has a close connection with HIV. There are five identified types of viral hepatitis and each one is caused by a different virus. In the United States, hepatitis A, hepatitis B and hepatitis C are the most common types. Hepatitis A is a liver disease caused by the hepatitis A virus (HAV), and can affect anyone. In the U. S., hepatitis A occurs in situations ranging from isolated cases, to widespread epidemics. Hepatitis B is a serious disease caused by a virus that attacks the liver. Known as hepatitis B virus (HBV), it can cause lifelong infection, cirrhosis (scarring) of the liver, liver cancer, liver failure, and death. Hepatitis C is a liver disease caused by the hepatitis C virus (HCV), which is found in the blood of persons who have the disease. HCV is spread by contact with the blood of an infected person. Hepatitis D is a liver disease caused by the hepatitis D virus (HDV), a defective virus that needs the HBV virus to exist. HDV is found in the blood of persons infected with the virus. Hepatitis E is a liver disease caused by the hepatitis E virus (HEV), transmitted in much the same way as hepatitis A virus. Hepatitis E, however, does not occur often in the United States.