These diseases are caused especially by some of the herpetic viruses, some of the enteroviruses, adenoviruses and human parvovirus B19. Known 8 human herpes viruses (HHV 1-8) are classified into 3 subfamilies – alpha, beta and gamma herpesvirinae.
Herpes simplex virus and varicella-zoster virus classified into alphaherpesvirinae, cytomegalovirus classified into betaherpesvirinae and Epstein-Barr virus from gammaherpesvirinae have the greatest clinical importace.