human herpesvirus 6, a T-cell lymphotrophic virus belonging to the subfamily Betaherpesvirinae that has a high affinity for CD4 lymphocytes. It exists as two variants, A and B. Variant A is isolated mainly in immunocompromised individuals. Variant B causes roseola infantum. Most healthy adults carry the virus and are asymptomatic; infection results in lifelong persistence. See also herpesvirus, roseola infantum.
