Human Herpesvirus 6 (HHV-6) is a set of two closely related herpes viruses known as HHV-6A and HHV-6B. HHV-6B infects approximately 70% of children by the age of three and often results in fever, diarrhea, sometimes with a rash known as roseola. Although rare, this primary infection HHV-6B infection can also cause febrile seizures, encephalitis or intractable seizures. Little is known about the prevalence of HHV-6A or how it is acquired.