I can understand your concern about genital herpes transmission. As you may also know, genital herpes is one of the worst known sexually transmitted disease and is one of the most common one. There are two types of virus, which causes herpes. They are the HSV type 1 and HSV type 2. Of these, HSV type 1 is what cause cold sores in mouth and facial areas. It causes fever sores, cold sores and blisters. HSV type 2 causes almost similar sores and blisters in genital areas. Both of these infections can be caused through sexual contacts and even through oral sex. Transmission can occur from an infected person who do not have visible sores or symptoms. But the diagnosis will be easier in people having blisters or sores, as from testing sores infection can be found easily. Doctors can find the sores visibly by inspecting it. Blood test for antibodies also help in detecting infection. It is better to continue sexual contact only after testing for infection.