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ABOUT HEPATITIS B

Hepatitis B is a disease caused by the hepatitis B virus (HBV) that affects the liver and can cause both acute and chronic disease. About 2 billion people worldwide have been infected with the virus, and approximately 400 million are chronically infected. Chronic HBV infection can lead to liver cirrhosis and hepatocellular carcinoma (HCC). The World Health Organization (WHO) estimates that there are 1 million HBV-related deaths each year, making it the tenth leading cause of death worldwide.

HBV is a blood-borne virus and can be transmitted horizontally by sexual transmission, by blood and blood-products, and intravenous drug use, but these forms of transmission are relatively low. Perinatal transmission remains the predominant cause of infection in highly endemic areas. Chronic hepatitis B occurs when infection persists for more than 6 months. The risk of chronic infection in adult-acquired infection is only 5% to 10%, while perinatally acquired infection carries an 85% to 95% risk of chronicity, and has a 25% to 30% lifetime risk of developing serious complications or fatal liver disease. Hepatitis B infection is a major global public health problem despite the availability of a highly effective vaccine and the use of antiviral therapy.

The prevalence of HBV infection varies greatly throughout the world with chronic HBV prevalence ranging from 0.2% to 20%. HBV infection is especially endemic in Asia, the South Pacific region, Sub-Saharan Africa, and in certain indigenous Arctic populations. This population acquires infection at a young age and is at much higher risk for long-term HBV complications by the fourth or fifth decade of life than people in developed countries, who acquire the disease largely in adulthood.

The progression of disease in patients with chronic hepatitis B is variable, and ranges from mild, asymptomatic infection to severe chronic liver disease. Liver damage is a consequence of a complex interaction between the host immune system and the infected liver cells. The course of chronic hepatitis B can be exacerbated by various factors, including coinfection with other viruses (e.g. hepatitis C and HIV) and alcohol consumption.

Eight HBV genotypes (A to H) have been identified which show a distinct geographical distribution. HBV genotypes B and C are prevalent in the Asia Pacific region, HBV genotypes A and D are prevalence in Europe, North America and the Mediterranean region, while HBV genotype E is typical for Africa and HBV genotype F is found in American natives and in Polynesia. The distribution of genotype G is not yet completely determined, but it appears to be global. It is not yet established whether disease progression and the development of HCC are more commonly associated with certain genotypes.

Hepatitis B is preventable with a safe and effective vaccine. The incidence of perinatal transmission has been significantly reduced in countries which implement a comprehensive infant immunization strategy. For individuals with chronic hepatitis B, several treatment options are available. These include interferon (alpha and pegulated) and five oral antiviral drugs. The goals of these treatments are to eliminate or permanently suppress viral replication, and to minimize liver damage. The management of these individuals is complex and requires careful ongoing monitoring to detect adverse side effects of therapy and to facilitate the early detection of antiviral resistance.

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