Last updated on:May 8th, 2022
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Hepatitis B virus (HBV) belongs to the Hepadnaviridae family. It is a double-stranded DNA virus. It is the most common chronic viral infection worldwide and it represents a global health problem. Patients present with a huge spectrum of clinical manifestations which varies in both acute and chronic disease. The liver is primarily involved. There is a safe and effective vaccine available for prevention. Long-term antiviral drugs can also help to reverse cirrhosis and hepatocellular carcinoma that are due to liver damage. The implementation of universal vaccination to infants has resulted in reduction of prevalence worldwide.
The prevalence of HBV infection varies by geography. Areas of low prevalence (<2%) include Western Europe, North America, Australia, and Japan. Areas of high prevalence (≥8%) include China, southeast Asia, and certain African countries. About 43% of all HBV-infected persons live in regions of intermediate prevalence (2–7%), including south-central and southwest Asia, eastern and southern Europe, Russia, and Central and South America.
HBV is transmitted via percutaneous inoculation, or mucosal exposure to infectious bodily fluids (i.e., blood or semen). Three modes of infection prevail. Mother-to-child transmission (perinatal transmission) is the predominant mode of transmission in high-prevalence areas. Unprotected sexual intercourse and injection drug use in adults is the leading cause of spread in low-prevalence areas. Transmission through unsafe injections, blood transfusions, or dialysis is still common in developing countries (intermediate-prevalence areas).
HBV infection primarily affects the liver. The pathogenesis of liver disease is mainly immune-mediated. Typically, the incubation period is between 30-180 days. Some acute HBV infections will resolve on their own, but some will develop into chronic infection. There is an inverse relationship between the risk of developing acute hepatitis and its progression to chronic infection and the age of the host. Infections during infancy carry a >90% chance of progressing to chronic infection; after the age of 5 years—and particularly in adults—>90% develop acute hepatitis and clear the virus within 6 months’ time.
HBV infection can be prevented via vaccination. Vaccines available include those with 2 dose-series, 3 dose-series or combined with hepatitis A. Most of them are based on recombinant DNA technology and express HbsAg only. About 95% of immunocompetent people achieve response to the vaccine. A titer of HBs >10mIU/mL is considered protective.