Herpes simplex infected cervical cell, light micrograph. Herpes simplex is a virus that causes cold sores and genital herpes. Genital herpes is usually caused by the HSV-2 virus (as here), while cold sores are more commonly caused by the related HSV-1. However, either virus can affect either area. Cells infected with HSV-2 characteristically develop many nuclei (dark purple), which causes them to grow in size. The nuclei contain the viral DNA. The virus is transmitted by contact. Herpes causes the appearance of a recurring sore or lesion on the genitals. There is no cure for the condition, as the virus hides in nerve cells.