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Sunday, January 25, 2009

Hepadnaviridae

Hepadnaviridae is a family of viruses that causes liver infections in humans and animals hence the name 'hepadnaviridae' where 'hepa' is the Latin word for liver. Some animals that can be infected with this family of viruses are ducks, birds, wooly monkeys, squirrels and many more.


Features of Hepadnaviridae viruses

The genome of the hepadnaviridae viruses contains a partial double stranded DNA with overlapping reading frames. As a result it is considered to be an RNA intermediate. Due to these properties, hepadnaviridae viruses are grouped under group VII (RNA reverse transcribing viruses) of the Baltimore classification scheme.


(Click to thumnail to view image)
Hepadnaviridae viruses also possess a spherical viral envelope made up of cellular lipids, glycoproteins and surface antigens and an icosahedral capsid.



Hepatitis B: Pathogenesis


The specific hepadnaviridae virus being discussed in this section will be the Hepatitis B virus (HBV). This virus is important due to its ability to infect humans and it being able to cause potentially life threatening liver infection.




About an estimated 600 000 people die each year due to it and 25% of adults who are chronically infected during childhood will die from liver cirrhosis. Upon infection, 90% of neonates, 50% of children and 5-10% of adults will develop chronic hepatitis B. The diagram below shows areas in the world that are at risk of infection.

(click image to enlarge)

The hepatitis B virus targets the liver cells and can cause the following symptoms during an acute infection:

  • yellowing of the skin and eyes (jaundice),
  • dark urine,
  • extreme fatigue,
  • nausea,
  • vomiting and
  • Abdominal pain.

(click image to enlarge)

Following an acute infection, chronic infection can occur which can result in liver cirrhosis and liver cancer. People with chronic hepatitis are still infectious and may not display any symptoms.

There are many types of hepatitis infections which can be grouped into chronic and acute infections. Chronic active hepatitis is the one that causes liver cirrhosis and liver cancer.The other types of hepatitis infections are shown below.


Hepatitis B: Transmission


The hepatitis B virus can be spread from person to person by various means such as:

  • blood contact
  • bodily fluid contact
  • from mother to baby at birth
  • early childhood infections
  • unsafe injection practices
  • sexual contact

The hepatitis B virus is very infectious and can survive outside the body for 7 days and has an average incubation period of 90 days.

Hepatitis B: Prevention

The hepatitis B infections can be prevented by avoiding risky sexual behavior and sharing of needles since it can spread via blood and bodily fluid contact. Moreover, there is a hepatitis B vaccine available which can prevent hepatitis B infections.


Hepatitis infections have been reduced over the years as since 1987 all babies are vaccinated against it.

Hepatitis B: Lab Diagnosis

Patients can be tested for the Hepatitis B virus using serological methods or liver biopsy.

Serological Methods

Under the serological methods, the blood serum can be tested for detectable hepatitis B virus surface antigen, envelope antigen in acute infections and IgM antibodies.

IgM antibodies are antibodies produced during the acute infection and IgG are the antibodies that persist after the acute infection to serve as the 'memory' which will help fight off subsequent acute infections. After an acute infection, IgM antibodies will start to diminish and the titer of IgG antibodies will start to increase.

The presence of these antibodies and antigens can be detected using an ELISA or blood test.

Liver Biopsy

The other method of diagnosing hepatitis B infection is using liver biopsy when tests using serological methods are positive. This is done to confirm the HBV infection and to assess the patient's condition and decide the treatment for the infection. Liver biopsy is done by removing a small piece of the person's liver which will be examined and tested.

(click image to enlarge)

Types of Hepatitis Viruses

The table below shows the different types hepatitis viruses and the modes of transmissions.


Videos

A Hepatitis information video which outlines the symptoms, transmission, prevention, diagnosis and treatment of hepatitis B.







References

Pictures:


  1. http://www.stanford.edu/group/virus/hepadna/2004tansilvis/hep%20b%20genome.gif
  2. http://www.who.int/entity/ith/maps/hepatitisB2007.jpg
  3. http://ontariohepatitistreatment.com/devel2/images/How_a_Biopsy_is_Performed.jpg
  4. http://www.phoenixpeptide.com/catalog/upload/pnxhighlights/pnxhighlights_000000056/notes/ELISA2.gif
  5. http://sg.wrs.yahoo.com/_ylt=A0S0zu7UFnxJ7msBPQMu4gt./SIG=135jkvjtj/EXP=1232955476/**http%3A//www.bioserv-diagnostics.com/images/jpg%2520rgb/AOA_ELISA_IG_typing_rgb.jpg
  6. http://www.mydietsolutions.com/mds/components/com_virtuemart/shop_image/product/8855aecf720f86ebce2c38801634727f.jpg
  7. http://medicalimages.allrefer.com/large/jaundice.jpg

Information

  1. http://www.stanford.edu/group/virus/hepadna/2004tansilvis/Basics.htm
  2. http://www.who.int/mediacentre/factsheets/fs204/en/



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