Hepatitis Delta (D) is a negative sense, single-stranded, closed circular RNA virus with a genome of approximately 1700bp. It is considered as a satellite virus since it can replicate only in the presence of the hepadnavirus (Hepatitis B virus suface antigene). 
Hepatitis delta virus (HDV) has an epidemiological distribution similar to HBV. It has been found worldwide with unequal distribution rates. There are around 10 million people infected with HDV around the world. It has mostly similar distribution patterns of HBV infection, but with different rates. There is a highest incidence HDV infection in Southern Italy, the Mediterranean region and in some parts of Africa and Asia. There is an average incidence of HDV infection in Turkey. 10% of the patients with HBV in the west and 15-25% of patients in the central and eastern regions have positive for anti-HDV. , 
Modes of Transmission
The modes of HDV transmission are mostly similar to those for HBV, including direct or indirect parenteral exposure to blood or body fluids, sexual and perinatal transmission. Sexual transmission is less efficient than that of HBV. Perinatal transmission occurs seldom since HDV infected mothers are generally anti-HBe positive and thus less infectious. 
The diagnosis and monitoring of HDV infection are mainly performed with serological tests based on determination of anti-HDV, IgM anti-HDV and nucleic acid tests based on detection of HDV-RNA in serum. This method got nullified in immunosuppressed patients with chronic or acute infection since HDV-Ag cannot be detected or rarely detected. The detection of HDV-RNA in serum is the most effective method of evaluating HDV-replication. It enables the detection where serological tests fail. Moreover quantification of HDV-RNA, may be an indicator in understanding of the pathophysiology of infection and also helps for the monitoring the severity of liver diseases and effect of treatment. 
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