HEPATITIS D DEFINITION

Hepatitis D (or delta, the Greek letter "D"), is a form of liver inflammation that occurs only in patients who also are infected by the hepatitis B virus. Infection by the hepatitis delta virus (HDV) either occurs at the same time as hepatitis B develops, or develops later when infection by hepatitis B virus (HBV) has entered the chronic (long-lasting) stage.

Delta hepatitis can be quite severe, but it is seen only in patients already infected by HBV. In the late 1970s, Italian physicians discovered that some patients with hepatitis B had another type of infectious agent in their liver cells. Later the new virus-HDV-was confirmed by experimentally infecting chimpanzees. When both viruses are present, acute infection tends to be more severe. Furthermore, patients with both infections are likelier than those with HBV alone to develop chronic liver disease, and, when it occurs, it is more severe.

About 300 million persons worldwide carry HBV. Of them, at least 5% probably also have delta hepatitis. In North America HDV infection appears to be less frequent: 4% of all patients with acute hepatitis B have HDV infection. The delta virus causes an estimated 2% of all cases of acute viral hepatitis in the United States. The rate of HDV infection varies widely in different parts of the world; it is a very serious infection in some countries and quite mild in others. Chronic delta hepatitis is a more serious disease than either chronic hepatitis B alone or hepatitis C.

Certain individuals-the same ones who are at increased risk of developing hepatitis B-are the prime candidates to be infected by HDV. For example:

• Not infrequently, HDV infection occurs in patients with chronic HBV infection who also have hemophilia, a bleeding disease. These patients are at risk because they require large amounts of transfused blood and blood products that may contain HDV.
• In some areas, one-fourth to one-half of patients with chronic HBV infection who inject themselves with illicit drugs become infected by HDV as well. Drug abusers who share contaminated needles are likely to infect one another.
• Patients who get HBV infection by sexual contact may also be infected by HDV, although the delta virus is less often spread in this way than is HBV itself. Between 10-25% of homosexual men with chronic HBV infection harbor the delta virus.
• Like hepatitis B, HDV infection may develop in healthcare workers who are victims of a needle stick, and it also can be spread within households when personal items such as a razor or toothbrush are shared.