ALEX BARTEL / SCIENCE PHOTO LIBRARY ALEX BARTEL / SCIENCE PHOTO LIBRARY
Herpes simplex virus infection. The Herpes simplex viruses are regarded as being the most common human virus parasites. Two types have been distinguished. Type 1 (HSV-1) infection used to be associated with most oral and central nervous system infections, with Type 2 (HSV-2) involved in genital herpes infections. This distinction is no longer clear-cut, due to a supposed increase in oral sexual activities. HSV-1 infection commonly occurs in childhood. After the primary infection, the virus persists in a latent state to re-appear and cause recurrent cold sores.
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