Hepatitis B is caused by the hepatitis B virus (HBV). HBV is a noncytopathic virus. This means that the virus itself does not cause direct damage to liver cells. Instead, it is the immune system’s aggressive response to the virus that usually leads to inflammation and damage to the liver (hepatitis). However, HBV can cause damage to the genetic material inside liver cells. This can lead to liver cancer, which, like hepatitis, can be fatal.
People who have not been infected with HBV can be vaccinated against the virus to prevent infection.
HBV is present in blood, semen and vaginal fluids and is transmitted primarily through sexual activity. Another major transmission route is sharing injection drug equipment (including needles, cookers, tourniquets) and, to a lesser extent, non-injection drugs (cocaine straws and crack pipes) due to the possibility of exposure to blood. Pregnant women who have hepatitis B can also transmit the virus to their babies, most likely during birth.
The number of new hepatitis B infections in the United States has declined from about 260,000 a year in the 1980s to about 43,000 in 2007, with the greatest decline occurring in children and adolescents as a result of routine HBV vaccination.
An estimated 800,000 to 1.4 million people in the United States have chronic HBV infection. Chronic hepatitis B is an even greater problem globally, affecting about 350 million people.
Nearly 620,000 people worldwide die from HBV-related liver disease each year.