Human herpesvirus 6 (HHV-6) is one of the eight known viruses that are members of the human herpes family. The Human herpesvirus 6 is a virus within the Betaherpesvirinae subfamily of the genus, Roseoloviruses. There are seven other types of viruses in this family. HHV-6 has two known variants: HHV-6A and HHV-6B. Although the two variants are highly distinctive, diagnostic tests are usually unable to distinguish the specific culprit of an infection. The virus makes its home in almost 100% of the human population all over the world. While HHV-6A has not been linked to any diseases, HHV-6B is the cause of the common childhood illness, sixth disease, a near-universal childhood disease and other febrile illnesses.
The classical presentation of HHV-6 is a high temperature followed by a rash, malaise and irritability, and in tympanic membrane inflammation.
Most primary infections are at an early age; primary infection in adults tend to be more severe.
Noone knows how this virus is transmitted, but it is thought that the most common way is possible through the saliva. Both HHV-6B and HHV-7 are found on human saliva. Studies report varying rates of prevalence of HHV-6 in saliva (between 3% – 90%), which might point to the salivary glands as a container for persistent or latent viral infections.
For more info on HHV-6 please see these articles:
Human Herpes Virus 6 http://cmr.asm.org/content/10/3/521.full.pdf+html
Prevalence of herpesvirus DNA in MS patients and healthy blood donors http://www.ncbi.nlm.nih.gov/pubmed/11903118
HHV Foundation http://www.hhv-6foundation.org/