Herpes is a common infection caused by a virus. Herpes is usually mild but can be serious in a patient treated for cancer.
There are two types of herpes simplex virus: hsv1 and hsv2. Their deoxyribonucleic acid (DNA) is similar in shape and organisation. 50% of their DNA is identical although their pathogenic potential, epidemiology, and usual clinical features on the skin or mucous membranes are different.
The viruses are fragile and can only be transmitted by direct skin or mucosal contact: kissing, hands contaminated by saliva, skin breaks, sexual intercourse, or childbirth. After initial contact (primary infection), which may or may not be apparent, the virus multiplies at the inoculation site and then spreads through the blood or along the nerves.
The usual lesions of herpes are vesicles on the skin or mucosal membranes. hsv1 infects the lips (cold sores) or the mouth and hsv2 affects the genital mucous membranes.