Hepatitis B virus (HBV) is a usual ...

Hepatitis B virus (HBV) is a usual cause of liver disease completely through the world. An estimated single third of the world's population has serologic evidence of past infection, and the virus causes more than 1 million deaths annually. (1) In the United States, the incidence of HBV infection declined from about 14 cases by means of 100,000 population in the mid-1980s to about three cases for 100,000 population in 1998. (2) However, there are still 125 million adults and children in the United States with chronic HBV infection.

HBV is transmitted by means of blood and other body fluids, including sperm and saliva. The virus is 100 times more infectious than human immunodeficiency virus (HIV) and, unlike HIV, it can live outside the corpse in dried blood for longer than a week. (3) In Southeast Asia, China, and sub-Saharan Africa, HBV infection usually is acquired perinatally or in early childhood, leading to a high prevalence of chronic infection (5 to 20 percent) In contrast, 80 percent of infections in the United States, Canada, and Western Europe meet the eye in adults via sexual contact or intravenous medicine use, leading to a abundant lower baseline prevalence (0.1 percent) In the United States, form into groupss at increased risk for HBV infection have been identified (Table 1) (4)

Because newborns have an immature immune method 90 percent of infants infected perinatally progres to chronic infection. Progression to chronic HBV infection come to one's minds in 25 to 30 percent of someones infected before five years of age, and in 3 to 5 percent of those infected later in childhood or as adults. Immunosuppressed patients are at greater risk of becoming chronically infected. (156)

Virologic Characteristics

HBV belongs to the Hepadnaviridae family of viruses. Its genome consists of partially double-stranded circular DNA. The DNA is enclos in a nucleocapsid, or core antigen, which is fence abouted by a spherical envelope (surface antigen). The entire virion is known as the Dane particle. In addition to the core and surface proteins, the HBV genome encode a DNA polymerase that also acts as a turn topsy-turvy transcriptase.

In the hepatocyte nucleus, the viral genome is turn abouted into covalently closed circular DNA (cccDNA). This cccDNA is the template for carrier RNA (mRNA). The mRNA transcribes viral proteins as well as "pre-genomic" RNA that is overthrow transcribed into the HBV DNA of just discovered virions. Without the reverse transcriptase, novel virions cannot be produced, and replication ceases. The core gene also brings a circulating peptide, the "e" antigen, that is associated with high of the same heights of viral replication. These antigens, as well as corresponding antibodies produc by means of the immune system, serve as useful laboratory markers of past, present or chronic infection (Tables 2 (5) and 3 (7))

Acute Infection

Acute HBV infection is subclinical in 70 percent of adults and 90 percent of children younger than five years. The incubation period after infection lasts single to four months. Symptoms of acute HBV infection include nausea, anorexia, fatigue, low-grade febrile affection and right upper quadrant or epigastric pain. Clinical jaundice appears as constitutional symptoms are resolving. Extrahepatic manifestations of acute HBV infection include myalgias, joint pain, and urticaria. Symptoms of acute disease explain by one to three month although a certain quantity of persons have prolonged fatigue. Treatment for acute infection is generally supportive, although a patients require hospitalization.

Hepatic transaminase flats (alanine transaminase [ALT] and aspartate transaminase [AST]) cogitate hepatocellular injury and range from several hundr to 20000 IU through L. These values tend to rise undivided to two weeks before the storming of jaundice. Serum bilirubin values are usually les than 20 mg by dL (342 [micro]mol per L) Mild anemia is used by all as is relative lymphocytosis. More stern disease results in an elevation in the prothrombin time and a decrease in the serum albumin plain HBV is not cytopathic, and liver injury is caused at the host's immune response against infected hepatocytes.

Acute HBV infection leads to fulminant hepatic failure from massive hepatocellular necrosis in about 1 percent of infections. Rarely, patients with an "exuberant" immune answer present with clinical symptoms still progress to hepatic decompensation, including encephalopathy and coagulopathy. Mortality is high, and liver transplantation many times is necessary. (8)

Chronic Infection

Chronic HBV infection is defined as hepatitis B surface antigen (HBsAg) positivity for at least six month (Table 4) (9) circulating thinking endorses the concept of four distinct stages of HBV infection, which may be used to describe acute and chronic disease. (59)

The first stage, the "immune tolerant" phase, is characterized on high levels of HBV DNA replication, hepatitis B e antigen (HBeAg) positivity, and normal serum transaminase evens In the acutely infected child or adult, this stage portray by actions the incubation period before immune rejoinder to HBV. In neonates, the immune-tolerant stage may last for years to decades.