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 moderate prevalence areas, the disease is predominantly spread among children. In high prevalence countries, such as China, vertical transmission is most common. Without intervention, a mother who is positive for the Hepatitis B surface antigen confers a 20% risk of passing the infection to her offspring at the time of birth. This risk is as high as 90% if the mother is also positive for the Hepatitis B e antigen.
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.
Hepatitis B Symptoms
Symptoms of Hepatitis B infection may lead to a chronic inflammation of the liver, leading to cirrhosis. In looking at the long term affects of Hep B, this type of infection dramatically increases the incidence of 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. Contents
Hepatitis B Solutions
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.
Prevention of Hep B
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.
Molecular Biology of Hepatitis B
The Hepatitis B virus particle consists of a proteinaceous core particle containing the viral genome in DNA form and an outer lipid-based envelope with embedded proteins. The envelope proteins are involved in viral binding and release into susceptible cells. The inner capsid relocates the DNA genome to the cell's nucleus where viral mRNAs are transcribed. Three subgenomic transcripts encoding the envelope proteins are made, along with a poorly understood transcript encoding the X protein, whose function is still under debate. A fourth pre-genomic RNA is transcribed, which is exported to the cytosol and translates the viral polymerase and core proteins. Polymerase and pre-genomic RNA are encapsidated in assembling core particles, where reverse transcription of the pre-genomic RNA to genomic DNA occurs by the polymerase protein. The mature core particle then exits the cell via normal secretory pathways, acquiring an envelope along the way.
Hepatitis B is one of a few known 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.
Posted by Staff at May 13, 2005 11:39 PMblog comments powered by Disqus
I was interested in the symptoms of hep b for self diagnosis. I was also surprised and then disappointed to find that there was a section on this with none of the above contents.
Posted by: Sally Barnett at March 3, 2006 1:15 AM
if I have antibodies come up pos on a hep test does that mean I have it or is it possable since I had the vaccine that it is coming up?
How long ago was the vaccine, and what are your enzyme levels and over all viral load saying? If you are just showing antibodies, than yes, this is most likely from the vaccine. After all, Vaccines are meant to provide us with antibodies. However, IF your enzymes are elevated, and/or you have a high viral load for Hep (b,c), than that would be a positive diagnosis for Hepatitis.
Posted by: jamie at September 26, 2006 11:24 PM