Question

Choose one of the forms of viral hepatitis (A–E) and explain one of the characteristics of this form of hepatitis (incubation period, carrier state, severity, or prevention). 

Answer 1

Hepatitis (inflammation of liver) viruses are viruses that attack or infect the liver. These viruses are of different types: A, B, C, D, and E. There is a possibility of a G virus too. Of these, A, B and C viruses are the most commonly found viruses. All of these viruses can cause acute hepatitis, however, only virus Bad n C causes chronic hepatitis.

Hepatitis B is a major health concern for humans as it can cause chronic infection. Hepatitis B infection can result in death due to liver cirrhosis and liver cancer. The virus is a DNA virus with an incomplete + strand. HBsAg, HBcAg and HBeAg are present on the virus with the HBsAg have four phenotypes: adw, adr, ayw and ayr.

Carrier State: Carrier state is the presence of hepatitis B antigen (HBsAg) in circulation for more than 6 months and can last lifelong. The virus may no longer be actively replicating during this stage. HBsAg is one of the major antigens present in hepatitis B virus. Hepatitis B carrier state is important as it causes severe effects on the liver. Effects of the HBsAg in blood vary from minor changes in liver function, chronic active hepatitis, cirrhosis, or even hepatocellular carcinoma. The carriers of hepatitis B may have a normal liver or develop liver cirrhosis. Liver cirrhosis takes around 4-5 years to develop. Some carriers may develop hepatocellular carcinoma. Carrier state may be a result of childhood infection than infection in adults. It is frequent in males mostly due to deficiencies in acquired or natural immunity. 5-10% of Infected adults exhibit a carrier state. Another HBeAg is common in young adults.

HBsAg appear first post infection, usually after 2-8 weeks before jaundice sets in, along with signs of liver damage. The next markers are DNA polymerase of virus and HBeAg. HBcAg is not visible in serum, despite its synthesis, as antibodies to these antigens are generated. Chronic HBsAg carriers have decreased specific cell mediated immunity. The carrier state is divided in two phases:

1) The virus replicates on this phase with production of HBeAg, viral DNA, and DNA polymerase. HBeAg is the antigen that determines the infectivity of the virus. This phase of chronic infectivity has replicative forms of HBV DNA in the liver. The virus replication will decline subsequently due to development of HBe antibodies.

2) HBsAg persists in this second phase even in the absence of active virus replication. The DNA of hepatitis B virus integrants in to the chromosomes of liver hepatocytes. This integration is important for development of transcription of HBsAg and can later be a stage for development of hepatocellular carcinoma.

The carriers that are e+ve have more infectivity than e-ve carriers. Chronic active hepatitis is more common in e+ve carriers as e antigen is important for active infectivity. However, e-ve carriers develop Cirrhosis and hepatocellular carcinoma (HCC) more frequently.