Human Herpesviruses in Hematologic Diseases

The members of the Herpesvirales containing more than 130 different herpesviruses have already been isolated from all animal species representing the higher steps of evolution. According to our knowledge, eight herpesviruses are classified as human herpesviruses: Herpes simplex virus 1 (Human herpesvirus 1, HHV-1), Herpes simplex virus 2 (Human herpesvirus 2, HHV-2), Varicella-zoster virus (Human herpesvirus 3, HHV-3), Epstein-Barr virus (Human herpesvirus 4, HHV-4), Cytomegalovirus (Human herpesvirus 5, HHV-5), Human herpesvirus 6 (HHV-6A and HHV-6B), Human herpesvirus 7 (HHV-7), and Human herpesvirus 8 (HHV-8 or Kaposi's sarcoma associated herpesvirus, KSHV). It is a characteritic of herpesviral infections that after the frequently fulminant initial infection, they persist in the neurons or the Band T-cells of the body throughout life. Sometimes they reactivate. With respect to lymphotropic human herpesviruses, HHV-4 and HHV-8 reproduce mainly in the B-cells, while HHV-5, HHV-6 and HHV-7 reproduce in Tcells. HHV-4 causes most of the infectious mononucleosis cases and can immortalize Blymphocytes. HHV-5 can also cause infectious mononucleosis. A significant part of primary infections occurs in an asymptomatic way. Immunsuppression makes virus reproduction easier. A wide range of diseases may appear in an immunodeficient state. HHV-6 was first described in 1986 and was isolated from patients suffering from lymphoproliferative disease. It infects CD4+ T-lymphocytes and it reproduces in them. Two variants of it, HHV6A and HHV-6B, are known. Variant B is the pathogen of exanthema subitum (roseola infantum) and it can also cause latent infection with fever, diarrhoea, neural symptoms, and hepatitis. After transplantation, HHV-6 can reactivate and it is able to replicate in liver-cells. HHV-6 can activate the replication of HHV-4; it reduces or increases the replication of HIV, and accelerates the expression of antigens coded by HPV. HHV-7 was isolated from CD4+ cells in 1990 and was purified from a healthy patient. It is the pathogen of pityriasis rosea, but it can also cause exanthema subitum. Additionally, it can create latent infection in Tlymphocytes and productive infection in salivary gland epithelial cells. During pregnancy, viremia is more frequent and may adopt urogenital, perigenital and congenital transmission. HHV-7 may play a role in cases of immunodeficient patients; in the case of immunosuppression HHV-6 and HHV-7 play the role of cofactor in states accompanied by