Hepatitis B Virus
Hepatitis B Virus (HBV) is a double-stranded DNA virus in the Hepadnaviridae family. The infectious particle is 42nm in diameter, with a genome 3200 nucleotides long. It has an outer envelope and an icosahedral nucleocapsid, which contains viral DNA polymerase and has a diameter of 27nm. The envelope contains the HBV surface antigen (HBsAg); this is the molecule to which anti-HBV antibodies are directed. The non-infectious hepatitis B particles are composed of HBsAg only and come in the form of filaments and spheres. Their only likely purpose is binding up antibodies so the infectious particles can remain free. In humans HBV infects hepatocytes where it replicates within the nucleus, but can also be found in smooth muscle, bone marrow, kidneys, thyroid glands and other sites.
HBV is usually transmitted from blood to blood and can be contracted via infected needles (IV drugs and tattoos), sexual contact, cuts, hemodialysis, vertical transmission at birth and blood transfusions. In developed countries blood is screened for the presence of HBsAg before transfusion. Unlike other forms of viral hepatitis, HBV cannot be transmitted by contaminated food or water. The CDC states that preventive measures for HBV infection are similar to those for HIV. Diagnosis of HBV can be made by the presence of HBsAg, which can be found in the serum a few weeks before onset of illness. The anti-HBsAg antibody is found weeks to months after infection and can last, in some cases giving life-long immunity.
Hepatitis B is found mostly in Africa, Southeast Asia, Indonesia, the Philippines, and parts of the Caribbean. In those areas all socioeconomic groups are affected with rates above 8%. Infection rates between 2% and 7% occur in central and southwest Asia Israel, Japan, parts of Europe, the Amazon River basin and Russia. Most other areas including northern and western Europe, North America, Australia, New Zealand, Mexico and the southern part of South America have low rates of infection (<2%). Chronic HBV carriers can spread the infection. Infection from carriers is low in North America and northern Europe (<0.5%), but is >10% in some areas of the Far East. 5,000 people in the US die from HBV each year and there are currently 1 million chronically infected people in the US. Worldwide 2 billion people have been infected, with 350 million chronically and 1.5 million die each year.
Symptoms include loss of appetite (anorexia), fever, nausea with vomiting and jaundice. In this case, jaundice is caused when extra subunits of hemoglobin called bilirubin build up in the body due to liver damage. The word hepatitis means inflammation of the liver and with HBV infection the liver is often enlarged and tender. A HBV infection can be acute or chronic. An acute infection can resolve itself spontaneously, with rates as high as 90-95% in adults, but is...