1750. Viral infection with haemolysis is seen in -
The hepatitis B virus consists of a core containing DNA and a DNA polymerase enzyme needed for virus replication. The core of the virus is surrounded by surface protein (Fig. 22.24). The virus, also called a Dane paicle, and an excess of its surface protein (known as hepatitis B surface antigen, HBsAg) circulate in the blood. Humans are the only source of infection. Hepatitis B is one of the most common causes of chronic liver disease and hepatocellular carcinoma worldwide. Approximately one-third of the world's population have serological evidence of past or current infection with hepatitis B and approximately 350-400 million people are chronic HBsAg carriers. Hepatitis B may cause an acute viral hepatitis; however, acute infection is often asymptomatic, paicularly when acquired at bih. Many individuals with chronic hepatitis B are also asymptomatic. The risk of progression to chronic liver disease depends on the source and timing of infection (Box 22.36). Veical transmission from mother to child in the perinatal period is the most common cause of infection worldwide and carries the highest risk of ongoing chronic infection. In this setting, adaptive immune responses to HBV may be absent initially, with apparent immunological tolerance. Several mechanisms contribute towards this: * Firstly, the introduction of antigen in the neonatal period is tolerogenic. * Secondly, the presentation of such antigen within the liver, as described above, promotes tolerance; this is paicularly evident in the absence of a significant innate or inflammatory response. * Finally, very high loads of antigen may lead to so-called 'exhaustion' of cellular immune responses. The state of tolerance is not permanent, however, and may be reversed as a result of therapy, or through spontaneous changes in innate responses, such as interferon alpha (IFN-a) and NK cells, accompanied by host-mediated immunopathology. Chronic hepatitis can lead to cirrhosis or hepatocellular , haemolysis carcinoma, usually after decades of infection (Fig. 22.25). Chronic HBV infection is a dynamic process that can be divided into five phases (Box 22.37); these are not necessarily sequential, however, and not all patients will go through all phases. It is impoant to remember that the virus is not directly cytotoxic to cells; rather, it is an immune response to viral antigens displayed on infected hepatocytes that initiates liver injury. This explains why there may be very high levels of viral replication but little hepatocellular damage during the 'immune- tolerant' phase Ref Davidson 23rd edition pg 875
Hepatitis-B
Hepatitis-C
Prolong fever
Hepatiitis-A
Haematology