identification of a herpes simplex labialis susceptibility region on human chromosome 21. | most of the united states population is infected with either herpes simplex virus type 1 (hsv-1), herpes simplex virus type 2, or both. reactivations of hsv-1 infection cause herpes simplex labialis (hsl; cold sores or fever blisters), which is the most common recurring viral infection in humans. | 2008 | 18199027 |