|Hepatitis B virus|
Originally known as serum hepatitis, Hepatitis B has only been recognized as such since World War II, and has caused current epidemics in parts of Asia and Africa. Hepatitis B is recognized as endemic in China and various other parts of Asia. Over one-third of the world's population has been or is actively infected by hepatitis B.
Hepatitis B is largely transmitted through exposure to bodily fluids containing the virus. This includes unprotected sexual contact, blood transfusions, re-use of contaminated needles and syringes, vertical transmission from mother to child during childbirth, and so on. The primary method of transmission depends on the prevalence of the disease in a given area. In low prevalence areas, such as the continental United States, IV drug abuse and unprotected sex are the primary method. In high prevalence countries, such as China, vertical transmission is most common. In moderate prevalence areas, the disease is predominantly spread among children.
Roughly 16-40% of unimmunized sexual partners of individuals with hepatitis B will be infected through sexual contact.
The virus that causes hepatitis B is a member of the Hepadnavirus family and it is composed of an icosahedral nucleocapsid (core) enclosing a circular, double-stranded DNA genome. The virus is unique amongst the DNA viruses in that it uses a reverse transcriptase to generate the genomic DNA to deliver to its progeny. Additionally, the DNA genome is incomplete on one strand.
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.
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 neonates that acquire the infection from their mother at birth will clear the infection. Seventy percent of those infected between the age of one to six will clear the infection. When the infection is not cleared, one becomes a chronic carrier of the virus.
There are currently several treatments for chronic hepatitis B that can increase a person's chance of clearing the infection. Treatments are available in the form of antivirals such as lamivudine and adefovir and immune system modulators such as interferon alpha. There are several other antivirals under investigation. Roughly, all of the currently available treatments, when used alone, are about equally efficacious. However, some individuals are much more likely to respond than others. It is not presently known if combination therapy offers any advantages. In general, each works by reducing the viral load by several orders of magnitude thus helping a body's immune system clear the infection. Treatment strategies should be individualized by a doctor and patient. Considerations include the risks associated with each treatment, a person's likelihood of clearing the virus with treatment, a person's risk for developing complications of persistent infection, and development of viral resistance with treatment.
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 that has never been vaccinated may also be treated with HBIG just after 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.
A recombinant vaccine is available to prevent hepatitis B.
Many countries now routinely vaccinate infants against hepatitis B. In many areas, vaccination against hepatitis B is also required for all healthcare workers. Booster doses are recommended every five to ten years for healthcare workers.
- NIH collection of links to relevant articles on Hepatitis B (http://www.nlm.nih.gov/medlineplus/hepatitisb.html)
- Hepatitis B Foundation, non-profit organization dedicated to the global problem of hepatitis B (http://www.hepb.org/)
- CDC webpage on Hepatitis B (http://www.cdc.gov/ncidod/diseases/hepatitis/b/index.htm)