HHV6, or Human herpesvirus 6, is one of nine known human herpes viruses. It comprises two variant species HHV-6A and HHV-6B within the genus, Roseoleovirus. The HHV6 virion is an enveloped, spherical double stranded DNA virus. Its genome is 162-Kbp long with 97 predicted genes. HHV6A and 6B are 90% identical in nucelotde sequence. Transmission of the virus is believed be mainly driven by shedding into the saliva. Effective detection has been demonstrated by western blotting of tonsils.