SEN diseases (Thom et al., 2010). HighSEN diseases (Thom et al., 2010). High

SEN virus (SEN-V) is a small, circular, single-stranded (ss), blood borne, non-envelope DNA virus (Sharifi et al., 2008) (Shibata et al., 2001). It belongs to the Circoviridae family, Circovirus genus and it contains approximately 3800 nucleotides (Abbasi, 2016) (Khazaal, Alhamdani, and Faeq, 2015). 

The SEN-V represent a subfamily of very heterogenous agent varying in nucleotide sequence by 15% to 50% from each other and by 40% to 60% from the prototype of TT virus family in the genus Circoviridae. (Alter, H. J.,2009)

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It was discovered in Italy by a group of researchers who aimed to search for a viral cause of those cases of post-transfusion hepatitis that are not caused by hepatitis B virus (HBV) or hepatitis C virus (HCV) (Mohamed et al., 2011). SEN-V nomenclature was obtained from the initials of the infected patient, a human immunodeficiency virus (HIV)–infected injection drug user from whom the virus was first separated (Tanaka, 2001). 

It is classified into nine different genotypes (A to I) which differ by at least 25% in their nucleotide sequences (Pirouzi et al., 2014) (Hosseini and Bouzari, 2016). The most predominant SEN-V genotypes are SEN virus D (SEN-V-D) and SEN virus H (SEN-V-H) which usually found in patients with hepatitis from an unknown origin (non A-E hepatitis), but less common in healthy blood donors sera (Pirouzi et al., 2014) (Karimi and Bouzari, 2010). SEN-V-D and SEN-V-H were also detected in patients with fulminant hepatitis which confirms that those two types may participate in causing liver diseases (Thom et al., 2010). High prevalence of SENV-H in cirrhotics may indicate its conceivable part in the advancement of cirrhosis. SEN-V genotype B, A and E are less commonly found in blood donors and do not contribute in causing non A to E hepatitis (Dehkordi and Doosti, 2011).SEN-V is distributed worldwide among healthy blood donors from various geographic regions. 
The high frequency level of SEN-V among thalassemic patients proves the route of blood transfusion (Karimi and Bouzari, 2010). It is also transmitted by: drug addiction by injection uses, hemodialysis and organ or haematological progenitor cells transplantation, and mother to fetus (Khazaal, Alhamdani, and Faeq, 2015). 
A study reveals that SEN-V not only hepatotropic but also able to liver
damage (Rizvi et al., 2013).