الفهرس 
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Abstract
Hepatitis B and hepatitis C viruses are important causes of liver disease worldwide. Both viruses share risk factors for infection and probably by means of various mechanisms can induce liver damage ranging from acute and chronic hepatitis to cirrhosis, and eventually hepatocellular carcinoma.
As both viruses share common modes of transmission their combined infection is quite a frequent occurrence, particularly in areas where the two viruses are endemic. Dual infection is identified by the presence of both HBsAg and anti HCV antibodies in the patients’ serum.
Hepatitis B virus infection in patients who lack detectable HBsAg is called occult hepatitis B infection, which is generally defined as detection of HBV DNA in the serum and/or liver tissue of patients who test negative for HBsAg.
Occult HBV can occur with or sometimes without serologic markers of previous HBV infection (anti HBs and anti HBc) this type of HBV infection may be related to low level HBV infection with subdetectable levels of HBsAg or infection with HBV variants that can not express S protein or any HBV proteins, also it is possible that some of these patients had transient acute HBV infection with clearance of HBsAg and decline of anti HBc and anti HBs titers to undetectable levels.