What Is Hepatitis B?
Hepatitis B is the most common serious liver infection in the world. It is caused by the hepatitis B virus that attacks and injures the liver. Two billion people (or 1 in 3) have been infected and about 300 million people are living with a chronic hepatitis B infection. Each year up to 1 million people die from hepatitis B despite the fact that it is preventable and treatable.
The hepatitis B virus (HBV) is transmitted through blood and infected bodily fluids. It can be passed to others through direct contact with blood, unprotected sex, use of illegal drugs, unsterilized or contaminated needles, and from an infected woman to her newborn during pregnancy or childbirth.
Hepatitis B is a “silent epidemic” because most people do not have symptoms when they are newly infected or chronically infected. Thus, they can unknowingly spread the virus to others and continue the silent spread of hepatitis B. For people who are chronically infected but don’t have any symptoms, their liver is still being silently damaged which can develop into serious liver disease such as cirrhosis or liver cancer.
The good news is that hepatitis B is preventable and treatable. There is a simple blood test to diagnose a hepatitis B infection. Testing is the only way to know for sure if you are infected. There is a safe vaccine to prevent hepatitis B. There are effective drug therapies that can manage a chronic hepatitis B infection, and a cure is within sight.
Hepatitis B and Your Liver
The liver is such an important organ that we can survive only one or two days if it completely shuts down - if the liver fails, your body will fail, too. Fortunately, the liver can function even when up to 80% of it is diseased or removed. This is because it has the amazing ability to regenerate - or create - itself from healthy liver cells that still exist.
If your body were an automobile, your liver would be considered the engine. It does hundreds of vital things to make sure everything runs smoothly:
- Stores vitamins, sugar and iron to help give your body energy
- Controls the production and removal of cholesterol
- Clears your blood of waste products, drugs and other poisonous substances
- Makes clotting factors to stop excessive bleeding after cuts or injuries
- Produces immune factors and removes bacteria from the bloodstream to combat infection
- Releases a substance called "bile" to help digest food and absorb important nutrients
The word “hepatitis” actually means “inflammation” of the liver. Thus, “hepatitis B” refers to inflammation of the liver caused by the hepatitis B virus. With early detection and appropriate follow-up medical care, people living with a chronic hepatitis B infection can expect to enjoy a long and healthy life.
The hepatitis B virus is a small DNA virus that belongs to the “Hepadnaviridae” family. Related viruses in this family are also found in woodchucks, ground squirrels, tree squirrels, Peking ducks, and herons.
Structure of the Hepatitis B Virus
The hepatitis B virus contains an outer envelope and an inner core.
- The outer envelope of the virus is composed of a surface protein called the hepatitis B surface antigen or "HBsAg". The HBsAg can be detected by a simple blood test and a positive test result indicates a person is infected with the hepatitis B virus.
- The inner core of the virus is a protein shell referred to as the hepatitis B core antigen or "HBcAg," which contains the hepatitis B virus DNA and enzymes used in viral replication.
Life Cycle of the Hepatitis B Virus
The hepatitis B virus (HBV) has a complex life cycle. The virus enters the host liver cell and is transported into the nucleus of the liver cell. Once inside the nucleus, the viral DNA is transformed into a covalently closed circular DNA (cccDNA), which serves as a template for viral replication (creation of new hepatitis B virus). New HBV virus is packaged and leaves the liver cell, with the stable viral cccDNA remaining in the nucleus where it can integrate into the DNA of the host liver cell, as well as continue to create new hepatitis B virus. Although the life cycle is not completely understood, parts of this replicative process are error prone, which accounts for different genotypes or “genetic codes” of the hepatitis B virus.