Occult Hepatitis B infection and immunity

Abstract

Chronic hepatitis B virus (HBV) infection is a major global problem despite the availability of an efficacious vaccine. In Chronic HBV infection, liver cirrhosis and hepatocellular carcinoma (HCC) are associated with considerable morbidity and mortality. The detection of hepatitis B virus surface antigen (HBsAg) in serum remains the mainstay in the diagnosis of Chronic HBV infection and screening for HBV in most developing countries. The majority of individuals positive for HBsAg are also positive for HBV DNA in the serum. Occult HBV infection is characterized by the presence of HBV DNA in the absence of detected HBsAg. Recovery from an acute hepatitis B virus (HBV) infection is associated with loss of HBV DNA from serum, hepatitis Be antigen seroconversion (HBeAg), hepatitis B surface antigen (HBsAg) seroconversion, and normalization of serum aminotransferases. These changes generally imply clearance of virus, but clinical observations have shown that reactivation of HBV infection can occur either spontaneously or after immunosuppression. Recent studies showed that immune response to HBV remains vigorously long after an acute infection. In addition, HBV DNA can be detected by polymerase chain reaction (PCR) assay in serum, liver and peripheral blood mononuclear cells more than a decade after an apparent recovery from HBV infection. These findings suggest that recovery from acute hepatitis B may not result in complete virus elimination but rather the immune system keeps the virus at very low levels. The availability of PCR assays for HBV DNA allows the detection of 10 2 copies /ml compared with 10 6 copies /ml using hybridization assays. Using PCR assays, HBV DNA has been detected in some subjects who are HBsAg negative including those with no serological markers of HBV infection.