Disease
Hepatitis B

Author
Karen Neff, BIOL 230, fall 2009

Causative Agents
Hepatitis B is an infection of the liver caused by the Hepatitis B virus, which is an enveloped DNA virus with an icosohedral capsid (def), belonging to the Hepadnaviridae family.  The virions of the virus are 42 nanometers (def) wide.  This family has the smallest genomes of all the viruses. The Hepatitis B virus consists of two DNA strands that are uneven.  It is very resistant, known to survive at -20°C for 15 years and 2 years at -80°C, as well as 6 months at room temperature and 7 days at 44°C.

Epidemiology
Hepatitis B causes both acute (def) and chronic (def) disease states.  Worldwide, approximately 2 billion people have been infected, with about 300 million living with chronic hepatitis. About 600,000 people all over the world die from chronic or acute infections every year.  Infection occurs more frequently in males than females.  In the U.S., 200,000 people are infected every year and 4,000-5,000 people die from each year from chronic liver disease or liver cancer caused by the virus. It is estimated that 1-1.25 million people in the U.S. are carriers.  In the United States, it is responsible for 5-10% of the cases of end stage liver disease and 10-15% of hepatocellular carcinoma (def).  Hepatitis B is 50-100 times more infectious than HIV.  Only humans and chimpanzees are susceptible to it. 

In China and some parts of Asia, Hepatitis B is endemic (def), with most people infected during childhood.  High rates of chronic infection exist in the Amazon, southeastern and south-central Europe, the Middle East, and India. 

Sexually active heterosexuals, homosexual men, and IV drug users are particularly susceptible people groups for this disease because of its method of transmission. 

Transmission
Transmission occurs through contact with blood or body fluids of an infected person.  Therefore, it can be transmitted through sex, IV drug use, contact with blood or open sores of an infected person, accidental needle sticks, and perinatally (def) during birth. 

In the United States, IV drug users, homosexual men, heterosexuals who have multiple sex partners, hemodialysis (def) patients, healthcare workers, staff or residents of facilities for the developmentally disabled, and travelers to countries with high rates of Hepatitis B infections have the greatest risk of infection. 

Signs and Symptoms
Hepatitis B attacks liver cells and causes an acute or chronic liver infection.  The incubation period for acute hepatitis is 1-6 months.  It presents with anorexia (def), nausea, vomiting, fever, right upper quadrant abdominal pain, dark urine, clay-colored bowel movements, extreme fatigue, and jaundice (def).  Hepatic encephalopathy (def), mental confusion, coma, somnolence (def), and sleep pattern disturbances may also be present. 

Chronic hepatitis is a recurring infection that can eventually lead to cirrhosis (def) of the liver and/or liver cancer.  Patients with chronic hepatitis may be asymptomatic, as healthy carriers, or present with the same symptoms as acute hepatitis.  Young children who are infected are most likely to develop chronic hepatitis.

An estimated 90% of healthy adults who contract the disease will recover and become virus free within six months. 

Prevention and Treatment
The main course of prevention is the Hepatitis B vaccine, and all infants should receive it.  Patients in the high risk groups should also receive it.  These include people who engage in high-risk sexual behavior, IV drug users, HIV patients, those with chronic liver disease, hemophilia (def) patients or patients who receive blood products, renal dialysis (def) patients, anyone in close contact with an infected person, travelers to countries where the virus is prevalent, organ transplant recipients and health care workers or those whose jobs put them at risk for contracting the disease. 

There is no medication available for treatment of acute Hepatitis B.  Treatment focuses on rest, replacement of fluids lost through vomiting and diarrhea, and maintaining adequate nutrition. 

Chronic hepatitis can be treated with interferon (def) and some anti-viral drugs, namely adefovir, dpivoxil, lamivudine, entecavir, and telbivudine, however, these drugs do not always cure the disease.  They are also expensive and not always available in developing countries. 

Some patients who develop cirrhosis are given liver transplants. 

Bibliography

Hepatitis B [Internet]. [Revised August 2008]. World Health Organization; [Cited 2008 Nov. 28].  Available from:  http://www.who.int/mediacentre/factsheets/fs204/en/

Pyrosopoulos, Nikolaos T.  2007.  Hepatitis B.  [Internet].  [Cited 2008 Nov. 28].  Available from :  http://www.emedicine.com/med/topic992.htm

Hepatitis B [Internet].  [Cited 2008 Nov. 29].  Available from:  http://www.dhpe.org/infect/hepb.html

Hepatitis B virus [Internet].  [updated August 2006].  [Cited 2008 Nov. 28].  Available from:  http://microbewiki.kenyon.edu/index.php/Hepatitis_B_virus