Hepatitis B is an infectious hepatitis caused by the hepatitis B virus (HBV). This infection has two phases; acute phase and chronic phase.

1. Acute hepatitis B refers to newly acquired infections. Affected individuals experience symptoms approximately 1 to 4 months after exposure to the virus. This is the incubation period of hepatitis B. In most people with acute hepatitis, symptoms resolve over weeks to months and they are cured of the infection. However, a small number of people develop a very severe, life-threatening form of acute hepatitis called fulminant hepatitis.
2. Chronic hepatitis B is an infection with HBV that lasts longer than 6 months. Once the infection becomes chronic, it never goes away completely.

Approximately 90% to 95% of infected adults are able to fight off the virus so their infection is cured. Only about 5% to 10% of adults infected with HBV go on to develop chronic infection. Children are at much higher risk for chronic infection than adults. Up to 90% of infected young children will fail to clear the virus from their bodies and go on to develop chronic infection.

About two-thirds of people with chronic HBV infection are chronic carriers. These people do not develop symptoms, even though they harbor the virus and can transmit it to other people. The remaining one third develops “chronic active” hepatitis, a disease of the liver that can be very serious and life threatening.

• The liver is an important organ that filters toxins out of the blood, stores energy for later use, helps with digestion, and makes substances that fight infections and control bleeding.
• The liver has an incredible ability to heal itself, but long-term inflammation caused by HBV can result in permanent damage.
• Scarring of the liver is called cirrhosis, a condition traditionally associated with alcoholism but one that is also caused by chronic active hepatitis B infection. When this occurs, the liver can no longer carry out its normal functions and may fail completely. The only treatment for liver failure is liver transplant.
• Chronic hepatitis B also can lead to a type of liver cancer known as hepatocellular carcinoma.
• Any of these conditions can be fatal. About 15% to 25% percent of people with chronic hepatitis B die of liver disease.

How common is hepatitis B infection? What is the scope of the problem?

Hepatitis B is the most common serious liver infection in the worldwide. About 350 million people are chronic carriers of HBV, of whom, more than 620,000 die from liver-related disease each year. According to the Centers for Disease Control (CDC), approximately 46,000 new cases of hepatitis B occurred in the United States in 2006. About 800,000 to 1.4 million Americans are chronic hepatitis B virus carriers, and the disease causes about 3,000 deaths each year.

In the United States, hepatitis B is largely a disease of young adults aged 20-50 years. This reflects the major modes of transmission of hepatitis B (sexual transmission, illicit drug use, exposure to infected blood) and the effect of universal vaccination of infants. In the United States, there has been a 75% decrease in newly diagnosed cases of hepatitis B during the past decade. This decrease is attributed to increased vaccination and to heightened public awareness of HIV/AIDS and the resulting safer sexual practices. Use of the vaccine has resulted in an 82% decrease in the number of new infections reported in the United States each year.

Hepatitis B is found throughout the world. Some countries have much higher rates of infection than the United States; for example, in Southeast Asia and Sub-Saharan Africa, as many as 15% to 20% of adults are chronically infected with hepatitis B.

What is hepatitis B virus?

The hepatitis B virus is a DNA virus, which means that its genetic material is made up of deoxyribonucleic acids. It belongs to a family of viruses known as Hepadnaviridae. The virus is primarily found in the liver but is also present in the blood and certain body fluids.

Hepatitis B virus consists of a core particle (central portion) and a surrounding envelope (outer coat). The core is made up of DNA and the core antigen (HBcAg). The envelope contains the surface antigen (HBsAg). These antigens are present in the blood and are used as markers in the diagnosis and evaluation of patients with suspected viral hepatitis.

How does hepatitis B virus cause liver injury?

The hepatitis B virus reproduces in liver cells, but the virus itself is not the direct cause of damage to the liver. In fact, the presence of the virus triggers an immune response from the body as the body tries to eliminate the virus and recover from the infection. This immune response causes inflammation and may seriously injure liver calls. Therefore, there is a balance between the protective and destructive effects of the immune response to the hepatitis B virus.