Spread of Hepatitis Virus

Hepatitis is an inflammation of the liver. This condition can resolve spontaneously or can progress to fibrosis, cirrhosis or hepatocellular carcinoma (HCC). Hepatitis viruses are the most common cause of hepatitis in the world but other infections, toxic substances and autoimmune diseases can also cause hepatitis. There are six main hepatitis viruses, referred to as types A, B, C, D, E and G. The hepatitis attributed to these six different viruses are of greatest concern because of the burden of illness and death they may cause and the potential for outbreaks and epidemic spread.

Hepatitis B virus (HBV) is a small, enveloped, hepatotropic virus with a partly double-stranded, circular DNA genome.

HBV is the prototype member of the hepadnaviridae family. Other animal hepadnaviruses, including woodchuck hepatitis virus (WHV), duck hepatitis B virus (HBV) were also known but do not seen to establish infections in people. However, they provide better model systems for the study of viral replication, pathogenesis and evaluation of antiviral drugs against HBV.

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Natural infections with HBV can be transient with resolution or result in chronic infection. Transient infection may be characterized by acute hepatitis and, in rare cases, fatal fulminant hepatitis may also occur. Chronic infection is a major public health burden affecting an estimated 350 – 400 million individuals worldwide and carries a high risk for the development of chronic active hepatitis, cirrhosis and primary hepatocellular carcinoma (HCC).

Since the time between infection and clinical illness in chronic infections is usually decades, there is a significant opportunity for therapeutic intervention.

It had been documented in many reports that most of chronic carrier's cases of HBV in the world acquired the infection neonatally from their infected mothers. There have been reports of transmission via blood consuming arthropods, but its public health significance has not been established. Most transmission can be accounted for by person to person contact through parenteral routes; however, the source of as many as one-third of the transmissions remains unclear. There are no natural animal intermediates or vectors, although replication is supported in chimpanzees and possibly tupaia. Despite the fact that most adulthood HBV infections are transient, approximately 1 to 5 % of people infected as adults and more than 90% of those infected as neonates fail to mount a sufficient immune response to clear the virus, and develop a life-long chronic infection. However, it had been seen that antibodies developed against the HBs envelope protein are protective.

Their appearance following natural infection is associated with resolution, and their elicitation following immunization is the basis of protection. Initially, subviral particles devoid of viral nucleic acid, purified from the circulation of chronic HBV carriers, were used as a vaccine and found to be efficacious. The first HBV vaccine to be developed was a subviral particle (hepatitis B surface antigen) purified from the inactivated plasma of asymptomatic carriers of HBV. This was followed by a vaccine developed from cloned HBV DNA fragments encoding the S protein, first in mouse L cells and then in yeast cells. Both plasma-derived and cell-based vaccines are safe and effective and have been utilized since the 1990s in some but not all parts of the world.