Enveloped DNA Virus- Hepadnaviridae

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picture courtesy of http:// www.saddleback.edu/alfa/N172/images/jaundic.jpg

The picture above shows a symptom of acute hepatitis B- jaundice.

WHAT IS HEPADNAVIRIDAE?

Hepadnaviridae (Hepa = liver; dna = deoxyribonucleic acid)

As their names imply, all of the known hepadnaviruses are hepatotropic, infecting liver cells, and all can cause hepatitis in their known host. Hepatitis is the a syndrome characterized by inflammation of the liver.

Unique Features Of The Genome

1. Partial dsDNA

2. Endogenous DNA-dependent DNA polymerase

3. Use of overlapping reading frame

4. RNA intermediate

1 virus that is pathogenic to man: Hepatitis B virus(HBV)!

picture courtesy of http://www.hivandhepatitis.com/2006icr/ddw/images/cirrhosis-liver.jpg

Pathogenesis

Acute or chronic liver infection is dependent on age of infection. The younger a person is when she becomes infected with HBV, the more likely she is to be asymptomatic and become a chronic carrier of the disease. Babies born to infected mothers are at very high risk of to becoming carriers and developing liver pathology. About 90% of adults who acquire HBV recover from it completely and become immune to the virus. The other 10% of cases are the people who become chronic carriers.

Clinical features- Acute and Chronic

Clinical Features (Acute)

• loss of appetite, nausea, vomiting, fever, abdominal pain and jaundice
  
• about 90%-95% adults recover without sequelae
  
• 5%-10% become chronically infected.
  

Clinical Features (Chronic)

• Carrier state-have no symptoms and no abnormalities on lab testing.
  
• Some will develop cirrhosis
  

Lab Diagnosis

Hepatitis surface antigen (HBsAg) first appears in the blood during the incubation period, while the virus is actively 'replicating' in liver cells.

In acute infection, the HBsAg usually disappears within 3 months of onset. The Hepatitis envelope antigen (HBeAg) and HBV DNA can also be detected in blood while the virus is actively replicating in the liver.

Diagnosis of HBV infection is generally made on the basis of serology.

Antibody to HBcAg (anti-HBc) rises first. As a generalisation, the detection of IgM antibody specific to the hepatitis B core is the primary indicator of acute infection. It usually appears at or just before the onset of symptoms and remains detectable for at least 6 months. Subsequently,IgG antibodies against core are produced.

As acute infection resolves, IgG antibodies against core antigen persist and IgM and HBsAG becomes undetectable.

So, most people who have had acute infection continue to have IgG antibodies against core antigen for life. The diagnosis and prognosis of hepatitis B is confirmed and assessed by liver biopsy.

Epidemiology

Mode of transmission: blood and sexual contact

Control

- Avoid risky sexual behaviours and sharing of needles.

In this lecture we were taught about the Heptitis B virus and reminded of the dangers of risky sexual contacts. No! I don't want to risk having liver cancer. What about you?