|
Hepatitis B virus (HBV) is a dangerous as a virus because it attacks the liver, thus inhibiting the functions of this vital organ. The virus causes persistent infection, chronic hepatitis, liver cirrhosis, hepatocellular carcinoma, and liver necrosis. Hepatitis B is not directly cytopathic. Instead, damage to the liver is mediated by the immune response. 11 This virus can to cause an acute infection, which appears 6 weeks to 6 months after exposure, as well as a chronic infection, which lasts for more than 6 months. It is common for acute infections to become chronic; the probability of someone becoming chronically infected with HBV is inversely related to the age of infection. Therefore, the younger a person is when she becomes infected with HBV, the more likely she is to become a chronic carrier of the disease. Thus, babies born to infected mothers are at very high risk of to becoming carriers and devoloping liver pathology. 19 Perinatal transmission is one common way that HBV is transmitted, along with transmission through sexual intercourse, mixing of blood products, and horizontal transmission among young children. Different modes of transmission are more prevalent in certain areas of the world and among certain high-risk groups, yet all areas of the world see HBV transmission through all of these avenues. About 90% of adults who acquire HBV recover from it completely and become immune to the virus. The other 10% of cases are the people who become chronic carriers. |
  |
Although anywhere from 50-67% of HBV infections are asymptomatic, 33-50% are symptomatic. Traditional symptoms of HBV infection include the following:
- Loss of appetite
- Jaundice (yellow skin and eyes)
- Nausea, with or without vomiting
- Fever
- Weakness, tiredness, inability to work or function for significant periods of time
- Abdominal pain
- Joint soreness
- Dark urine
- Muscle pain
image taken from Dr. Clarence Wong. www.hepnet.com
From the figure above, it is clear that most exposed adults eventually reach a full recovery. Unfotunately, neonatal exposure is more serious and results in a much greater likelihood of hepatocellular carcinoma. These symptoms are common to all viral Hepatitis infections. In order to obtain a definitive diagnosis it is necessary to do a serological test to confirm the presence of Hepatitis B surface antigen (HBsAg) . In acute infection, HBsAg and immunoglobulin M (IgM) will be present in the serum. The IgM is anti-Hepatitis B core antigen (HBcAg) immunoglobulin and anti-Hepatitis B envelope antigen (HBeAg) immunoglobulin. The presence of anti-HBsAg IgG indicates convalescence of the acute infection as this is the neutralizing antibody that serves as the correlate of immunity for HBV. Its presence indicates the end of acute infection and a state of immunity towards HBV. In contrast, HBsAg itself can be detected in the serum of chronic carriers for more than 6 months, often for life. In addition, the HBeAg is also detectable, while the IgM anti-HBcAg becomes indetectable about 6 to 9 months post infection. Link to our Virus Page to learn more about HBV itself.
Although both the humoral and cell-mediated branches of the immune system are required to eliminate HBV infection, it is believed that chronic infections develop as the result of a weak T helper (Th) cell response to the virus, in particular to the HBsAg. It is this T cell response that is responsible for clearing the infected cells in the host's system. When this clearance is inefficient, and the infected cells persist in the body, a chronic infection develops. The humoral branch of the immune system is responsible for clearing the actual free virus particles from the host's system. 19
data taken from Mahoney and Kane, 1999. 19 Following the titer of HBsAG and anti-HBs is a good way to understand the progression of infection. As the HBsAg titer increases, the patient moves into acute, symptomatic disease. When the titer of anti-HBs rises, the symptoms begin to decline and patient reaches the immune state. data taken from Mahoney and Kane, 1999. 19 When an individual becomes a chronic carrier of the virus, anti-HBs never appears, and the high levels of HBsAg remain in the serum.
In the case of acute HBV infection, no specific medical treatment currently exists. However, in the case of chronic infections, a number of antiviral medications have been tested. As of now, the treatment for chronic HBV infection is a protocol which consists of treatment with Interferon-alpha2b, which is FDA approved. The goal of this treatment has two parts: to eliminate the serological markers of HBV including the presence of HBsAg, and to improve the condition of the liver disease. The figure below represents the way in which this interferon is thought to work to suppress viral replication and clear the chronic infectious state of HBV. It is thought that IFN-alpha2b increases the ability of the innate immune system to recognize and attack HBV-infected cells and thus contribute to decreasing any inflammatory reactions. In this way, it is believed that IFN-alpha2b stimulates the clearance of chronic HBV infection. Thus far, it looks as if approximately 1/3 of the people on this treatment respond strongly to it, and of those that respond, remission seems to be long-lived. www.hepnet.com
See our Vaccine Future Page for another approach to clearing chronic infection that is still in the experimental stage.
image taken from www.hepnet.com
Epidemiology Virus Pathology and Treatment
The Vaccine The Vaccine Future Vaccine Issues
References Back to Front Links
