Hepatitis B – HBV- Epidemiology

Epidemiology

Prevalence

Prevalence of Hepatitis B virus as of 2005.

The primary method of transmission reflects the prevalence of chronic HBV infection in a given area. In low prevalence areas such as the continental United States and Western Europe, where less than 2% of the population is chronically infected, injection drug abuse and unprotected sex are the primary methods, although other factors may be important. In moderate prevalence areas, which include Eastern Europe, Russia, and Japan, where 2-7% of the population is chronically infected, the disease is predominantly spread among children. In high prevalence areas such as China and South East Asia, transmission during childbirth is most common, although in other areas of high endemicity such as Africa, transmission during childhood is a significant factor. The prevalence of chronic HBV infection in areas of high endemicity is at least 8%.

Transmission

Transmission of Hepatitis B virus results from exposure to infectious blood or body fluids containing blood. Possible forms of transmission include (but are not limited to) unprotected sexual contact, blood transfusions, re-use of contaminated needles & syringes, and vertical transmission from mother to child during childbirth. Without intervention, a mother who is positive for HBsAg 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 HBeAg. HBV can be transmitted between family members within households, possibly by contact of nonintact skin or mucous membrane with secretions or saliva containing HBV. However, at least 30% of reported Hepatitis B among adults cannot be associated with an identifiable risk factor.

Medical aspects

Prevention

HBsAg

Several vaccines have been developed for the prevention of Hepatitis B virus infection. These rely on the use of one of the viral envelope proteins (Hepatitis B surface antigen or HBsAg). The vaccine was originally prepared from plasma obtained from patients who had long-standing Hepatitis B virus infection. However, currently, these are more often made using recombinant DNA technology, though plasma-derived vaccines continue to be used; the two types of vaccines are equally effective and safe.

Following vaccination Hepatitis B Surface antigen may be detected in serum for several days; this is known as vaccine antigenaemia.Vaccine is generally administered in either a two, three, or four dose schedules; and can be received by infants to adults. It provides protection for 85-90% of individuals, and lasts for 23 years.

Unlike Hepatitis A, Hepatitis B does not generally spread through water and food. Instead, it is transmitted through body fluids, from which prevention is taken to avoid: unprotected sexual contact, blood transfusions, re-use of contaminated needles and syringes, and vertical transmission during child birth. Infants may be vaccinated at birth.

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