HEPADNAVIRIDAE

• Hepadnaviridae is obtained from the hepatotrophic (replicates and cause infection of the liver) nature of the virus and its genome which is made up of double stranded DNA (hepadna).
  
• All hepadna viruses can cause hepatitis to their host as they infect hepatocytes that can be found in the liver.
  
• Hepatitis: Syndrome characterized by inflammation of the liver.
  
• Although all hepadnaviruses cause hepatitis to their host, but this does not mean that all hepatitis diseases are hepadna.
  
• Other hepatitis include:
  - Hepatitis A (Picornaviridae)
  - Hepatitis C (Flaviviridae)
  - Hepatitis D (No family)
  - Hepatitis E (Hepeviridae)
  - Hepatitis G (Flaviviridae)

from left in the top row:


Hepatitis A (http://www.marlerblog.com/gech_0001_0002_0_img0129(1).jpg)
Hepatitis C (http://www.co.monroe.mi.us/Monroe/uploadedImages/hepatitis-c(1).gif)
Hepatitis D (http://www.dshs.state.tx.us/idcu/disease/hepatitis/hepatitis_d/image1.gif)
Hepatitis E (http://pathmicro.med.sc.edu/virol/hep-e1.jpg)
Hepatitis G (http://www.dshs.state.tx.us/idcu/disease/hepatitis/hepatitis_g/image1.gif)

• Hepadnaviridae can be divided into two genera: Orthohepadnavirus and Avihepadnavirus.
  
• The genera are divided based on the similarities of the DNA sequence.
  
• The orthohepadnavirus infect mammals whereas the avihepadnavirus infect the avians meaning the birds.
  
• These viruses infect species that are closely related to their natural host. Example hepatitis B viruses infect humans and chimps which are closely related. That is why they have a narrow range of hosts.
  

• Among the virus classified under hepadnaviridae, only one virus that is pathogenic to human: Hepatitis B.


• Structure of hepadna virus:
  

Genome:
a. Hepatitis B has the smallest genome of 3.2 kb long among all hepadna viruses.
b. Partially double stranded DNA genome which carries all the genetic information in it.
c. The DNA consists of a positive strand and negative strand.
d. The complete negative strand is longer than of the incomplete positive strand (about 15% to 50% of the DNA is single stranded).
e. An RNA oligonucleotide is attached to the 5’ end of the positive strand while a 5’ protein covalently attached to the end of the negative strand.

Nucleocapsid:
a. Has an icosahedral shape.
b. The nucleocapsid is about 27 nm in diameter.
c. Contains a DNA polymerase and an antigen (HBcAg)
d. Three proteins can be found on the surface of the capsid: L (large), M (medium) and S (small) that is present in the ratio of 1:1:4.


Envelope:
a. It is spherical and 42 nm in diameter.
b. It surrounded the nucleocapsid.
c. Contain glycoproteins, lipids and surface antigens that is virus-specific like HBsAg.






References:

• http://www.taxonomy.nl/taxonomicon/TaxonTree.aspx?id=214545
• http://www.stanford.edu/~swhwang/10things.html
• www.marlerblog.com/.../hepatitis-a/
• http://www.care-mates.com/
• http://www.dshs.state.tx.us/idcu/disease/hepatitis/hepatitis_d/
• http://pathmicro.med.sc.edu/virol/hepatitis-virus.htm
• www.dshs.state.tx.us/.../hepatitis_g/faqs/
• virus.stanford.edu/hepadna/index.html