Hepatitis B is one of a few known non-retroviral viruses which employ reverse transcription as part of its replication process. Other viruses which use reverse transcription include HTLV or HIV, the virus that causes AIDS, but HIV and hepatitis B are not related. Hepatitis B's genome is DNA, and reverse transcription is one of the latter steps in making new viral particles, whereas HIV has an RNA genome and reverse transcription is one of the first steps in replication.

Transmission

Roughly 16-40% of unimmunized sexual partners of individuals with hepatitis B will be infected through sexual contact. The risk of transmission is closely related to the rate of viral replication in the infected individual at the time of exposure.

Immunopathogenesis

Clinical consequences and complications

The greater a person's age at the time of infection, the greater the chance their body will clear the infection. More than 95% of people who become infected as adults or older children will stage a full recovery and develop protective immunity to the virus. However, only 5% of new-borns that acquire the infection from their mother at birth will clear the infection. Of those infected between the age of one to six, 70% will clear the infection. When the infection is not cleared, one becomes a chronic carrier of the virus.

Acute infection with hepatitis B virus is associated with acute viral hepatitis -- an illness that begins with general ill-health, loss of appetite, nausea, vomiting, bodyaches, mild fever, and then progresses to development of jaundice. The illness lasts for a few weeks and then gradually improves in most of the affected people. A few patients may have more severe liver disease (fulminant hepatic failure), and may die as a result of it. The infection may also be entirely asymptomatic and may go unrecognized.

Chronic infection with hepatitis B virus may be either asymptomatic or may be associated with a chronic inflammation of the liver (chronic hepatitis), leading to cirrhosis over a period of several years. This type of infection dramatically increases the incidence of liver cancer.

Hepatitis D infection requires a concomitant infection with hepatitis B. Co-infection with hepatitis D increases the risk of liver cirrhosis and subsequently, liver cancer.

Polyarteritis nodosa is more common in people with hepatitis B infection.

Diagnosis

Shortly after the appearance of the HBsAg, another antigen named as the hepatitis B e antigen (HBeAg) will appear. Traditionally, the presence of HBeAg in a host's serum is associated with much higher rates of viral replication; however, some variants of the hepatitis B virus do not produce the 'e' antigen at all, so this rule does not always hold true. During the natural course of an infection, the HBeAg may be cleared, and antibodies to the 'e' antigen (anti-HBe) will arise immediately afterward. This conversion is usually associated with a dramatic decline in viral replication. If the host is able to clear the infection, eventually the HBsAg will become undetectable and will be followed by antibodies to the hepatitis B surface antigen (anti-HBs). A person negative for HBsAg but positive for anti-HBs has either cleared an infection or has been vaccinated previously. A number of persons who are positive for HBsAg may have very little viral multiplication, and hence may be at little risk of long-term complications or of transmitting infection to others.

More recently, PCR tests have been developed to detect and measure the amount of viral nucleic acid in clinical specimens. These tests are useful to assess a person's infection status and to monitor treatment.

Treatment

On March 29, 2005, the US Food and Drug Administration (FDA) approved Entecavir for the treatment of hepatitis B.

On February 25, 2005, the EU Commission approved PEGASYS for the treatment of hepatitis B making it the first pegylated interferon to be approved for hepatitis B.

Chronic carriers should be strongly encouraged to avoid consuming alcohol as it increases their risk for cirrhosis and hepatocellular carcinoma (liver cancer).

Infants born to mothers known to carry hepatitis B can be treated with antibodies to the hepatitis B virus (hepatitis B immune globulin or HBIg). When given with the vaccine within twelve hours of birth, the risk of acquiring hepatitis B is reduced 95%. This treatment also allows a mother to safely breastfeed her child.

An individual exposed to the virus who has never been vaccinated may be treated with HBIg immediately following the exposure. For instance, a health care worker accidentally stuck by a needle used in a hepatitis B carrier would qualify. Treatment must be soon after exposure, however.

Prevention

Many countries now routinely vaccinate infants against hepatitis B. In many areas, vaccination against hepatitis B is also required for all health-care workers. Some college campus housing units now require proof of vaccination as a prerequisite. Booster doses are not needed for low-risk general population. Some recommend such doses every five to ten years for health-care workers, though the evidence supporting such doses is quite limited.

The vaccine is highly effective. In endemic countries with high rates of hepatitis B infection, vaccination of newborns has not only reduced the risk of infection, but has also led to marked reduction in liver cancer. This was reported in Taiwan where a nationwide hepatitis B vaccination program was implemented in 1984 was associated with a decline in the incidence of childhood hepatocellular carcinoma. }} In that sense, this vaccine can be thought of as an anti-cancer vaccine.

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