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  Hepatitis B
is caused by a DNA virus identified in a spherical particle (d particle)
of 42 nm diameter, with an isometric capsid, a circular bicatenary DNA
genome and a pericapsidic involucre of cellular origin.
Hepatitis B virus (HBV) is a very resistant pathogen: it survives at room
temperature (up to six months), it endures cold (below 20°C up to several
years), heat (60°C up to 4 hours) and UV irradiation.
It is inactivated by high temperatures (121°C) and by stove and autoclave
treatment.
HBV virus is highly infective, in fact it has been estimated that it is
100 times more infective than HIV virus. The virus is present in all
bodily liquids and secretions (blood, saliva, sperm, vaginal secretions,
urine).
The virus is mainly spread by:
- the parenteral or percutaneous route: injections, cuts, transfusions,
blood products.
- the sexual route: genital mucosa lesions, oral mucosa lesions.
- the vertical route: from mother to fetus.
- the perinatal route: mixing of blood during delivery.
In the hospital environment the transmission of HBV can occur through
accidental percutaneous prick with needles or sharp contaminated objects,
contact with infected blood through solutions of continuity of the skin,
contamination of mucous membranes.
Once the infection has been contracted, about 90% of the subjects recover
completely and 5-10% become chronic carriers of the virus. Amongst the
latter 20-25% develop active chronic hepatitis which may lead to
cirrhosis and liver carcinoma. About 0.5-1% of the subjects develop acute
fulminant hepatitis which generally leads to death.
The risk of HBV infection following one single accidental exposure is
between 2 and 40% depending on the HBeAg state of the patient source of
infection.
For additional information
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