Hepatitis B

Hepatitis B virus surface antigen. Transmission electron Micrograph

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Definition:
Hepatitis B is the most common serious liver infection in the world. It is thought to be the leading cause of liver cancer.The World Health Organization estimates that hepatitis B infections lead to more than one million deaths every year.

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Virus classification:-
Group: Group VII (dsDNA-RT)
Family: Hepadnaviridae
Genus: Orthohepadnavirus
Species: Hepatitis B virus

Hepatitis B virus infects the liver of hominoidae, including humans, and causes an inflammation called hepatitis. It is a DNA virus and one of many unrelated viruses that cause viral hepatitis. The disease was originally known as “serum hepatitis” and has caused epidemics in parts of Asia and Africa. Hepatitis B is endemic in China and various other parts of Asia. The proportion of the world’s population currently infected with the virus is estimated at 3 to 6%, but up to a third have been exposed. Symptoms of the acute illness caused by the virus include liver inflammation, vomiting, jaundice, and rarely, death. Chronic hepatitis B may eventually cause liver cirrhosis and liver cancer, a fatal disease with very poor response to current chemotherapy. The infection is preventable by vaccination.

Symptoms:
The virus can cause a range of problems, including fever, fatigue, muscle or joint pain, loss of appetite, nausea and vomiting.

Chronic carriers have an increased risk of developing liver disease such as cirrhosis or liver cancer, because the hepatitis B virus steadily attacks the liver.

Chronic carriers will usually have on going inflammation of the liver and may eventually develop cirrhosis and liver cancer.

About 1% of people who are infected develop an extreme form of disease called acute fulminant hepatitis.

This condition can be fatal if not treated quickly. Sufferers may collapse with fatigue, have yellowing of the skin and eyes (jaundice) and develop swelling in their abdomen.

Hepatitis B virus infection may either be acute (self-limiting) or chronic (long-standing). Persons with self-limiting infection clear the infection spontaneously within weeks to months.

Children are less likely than adults to clear the infection. More than 95% of people who become infected as adults or older children will stage a full recovery and develop protective immunity to the virus. However, only 5% of newborns that acquire the infection from their mother at birth will clear the infection. Of those infected between the age of one to six, 70% will clear the infection.

Acute infection with hepatitis B virus is associated with acute viral hepatitis – an illness that begins with general ill-health, loss of appetite, nausea, vomiting, body aches, mild fever, dark urine, and then progresses to development of jaundice. It has been noted that itchy skin has been an indication as a possible symptom of all hepatitis virus types. The illness lasts for a few weeks and then gradually improves in most affected people. A few patients may have more severe liver disease (fulminant hepatic failure), and may die as a result of it. The infection may be entirely asymptomatic and may go unrecognized.

Chronic infection with Hepatitis B virus may be either asymptomatic or may be associated with a chronic inflammation of the liver (chronic hepatitis), leading to cirrhosis over a period of several years. This type of infection dramatically increases the incidence of hepatocellular carcinoma (liver cancer). Chronic carriers are encouraged to avoid consuming alcohol as it increases their risk for cirrhosis and liver cancer. Hepatitis B virus has been linked to the development of Membranous glomerulonephritis (MGN).

Hepatitis D infection can only occur with a concomitant infection with Hepatitis B virus because the Hepatitis D virus uses the Hepatitis B virus surface antigen to form a capsid. Co-infection with hepatitis D increases the risk of liver cirrhosis and liver cancer. Polyarteritis nodosa is more common in people with hepatitis B infection.

Causes:The disease is caused by the hepatitis B virus (HBV) that attacks the liver. The virus is transmitted through blood and bodily fluids that contain blood.This can occur through direct blood-to-blood contact, unprotected sex, and illicit drug use. It can also be passed from an infected woman to her new-born during the delivery process.

Risk Factor:It is thought that about one in three of the world’s population is infected by HBV.However, about 50% of those who carry the virus never develop any symptoms.
About nine out of ten people infected with HBV will eventually clear the virus from their bodies. But about 5-10% of infected adults will become chronic hepatitis B carriers, often without even knowing it.

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Diagnosis:The tests, called assays, for detection of hepatitis B virus infection involve serum or blood tests that detect either viral antigens (proteins produced by the virus) or antibodies produced by the host. Interpretation of these assays is complex.

The hepatitis B surface antigen (HBsAg) is most frequently used to screen for the presence of this infection. It is the first detectable viral antigen to appear during infection. However, early in an infection, this antigen may not be present and it may be undetectable later in the infection as it is being cleared by the host. The infectious virion contains an inner “core particle” enclosing viral genome. The icosahedral core particle is made of 180 or 240 copies of core protein, alternatively known as hepatitis B core antigen, or HBcAg. During this ‘window’ in which the host remains infected but is successfully clearing the virus, IgM antibodies to the hepatitis B core antigen (anti-HBc IgM) may be the only serological evidence of disease.

Shortly after the appearance of the HBsAg, another antigen named as the hepatitis B e antigen (HBeAg) will appear. Traditionally, the presence of HBeAg in a host’s serum is associated with much higher rates of viral replication and enhanced infectivity; however, variants of the hepatitis B virus do not produce the ‘e’ antigen, so this rule does not always hold true. During the natural course of an infection, the HBeAg may be cleared, and antibodies to the ‘e’ antigen (anti-HBe) will arise immediately afterwards. This conversion is usually associated with a dramatic decline in viral replication.

If the host is able to clear the infection, eventually the HBsAg will become undetectable and will be followed by IgG antibodies to the hepatitis B surface antigen and core antigen, (anti-HBs and anti HBc IgG). A person negative for HBsAg but positive for anti-HBs has either cleared an infection or has been vaccinated previously.

Individuals who remain HBsAg positive for at least six months are considered to be hepatitis B carriers. Carriers of the virus may have chronic hepatitis B, which would be reflected by elevated serum alanine aminotransferase levels and inflammation of the liver, as revealed by biopsy. Carriers who have seroconverted to HBeAg negative status, particularly those who acquired the infection as adults, have very little viral multiplication and hence may be at little risk of long-term complications or of transmitting infection to others.

More recently, PCR tests have been developed to detect and measure the amount of viral nucleic acid in clinical specimens. These tests are called viral loads and are used to assess a person’s infection status and to monitor treatment.


Treatment:-
Acute hepatitis B infection does not usually require treatment because most adults clear the infection spontaneously. Early antiviral treatment may only be required in fewer than 1% of patients, whose infection takes a very aggressive course (“fulminant hepatitis”) or who are immunocompromised. On the other hand, treatment of chronic infection may be necessary to reduce the risk of cirrhosis and liver cancer. Chronically infected individuals with persistently elevated serum alanine aminotransferase, a marker of liver damage, and HBV DNA levels are candidates for therapy.

There are several drug treatments available to treat hepatitis B.Patients may be put on a four month course of injections of the drug interferon.

An alternative treatment is a drug called lamivudine which is taken orally once a day. Treatment is usually for one year. Sometimes lamivudine is combined with interferon.

Although none of the available drugs can clear the infection, they can stop the virus from replicating, and prevent liver damage such as cirrhosis and liver cancer. Treatments include antiviral drugs such as lamivudine, adefovir and entecavir, and immune system modulators such as interferon alpha. However, some individuals are much more likely to respond than others and this might be because of the genotype of the infecting virus or the patient’s heredity. The treatment works by reducing the viral load, (the amount of virus particles as measured in the blood), which in turn reduces viral replication in the liver.

On March 29, 2005, the US Food and Drug Administration (FDA) approved Entecavir for the treatment of Hepatitis B. On February 25, 2005, the EU Commission approved Peginterferon alfa-2a (Pegasys). On October 27, 2006, telbivudine gained FDA approval. It is marketed under the brand name Tyzeka in the US and Sebivo outside the US. It is approved in Switzerland.

Infants born to mothers known to carry hepatitis B can be treated with antibodies to the hepatitis B virus (hepatitis B immune globulin or HBIg). When given with the vaccine within twelve hours of birth, the risk of acquiring hepatitis B is reduced 95%. This treatment allows a mother to safely breastfeed her child.

Chronic patients may require a liver transplant…....CLICK & SEE

Prevention:It can be prevented by the use of a safe and effective vaccine.However, for the 400 million people world-wide who are already carriers of HBV, the vaccine is of no use.

Vaccination: 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 .

Disclaimer: This information is not meant to be a substitute for professional medical advise or help. It is always best to consult with a Physician about serious health concerns. This information is in no way intended to diagnose or prescribe remedies.This is purely for educational purpose.
Resources:
http://news.bbc.co.uk/2/hi/health/1505615.stm
http://en.wikipedia.org/wiki/Hepatitis_B

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