AIDS is an acronym for acquired immune deficiency syndrome. It is a viral disease that weakens a person's immune system. When a person's immune system is weakened, it is more vulnerable to an outside influence such as another disease. So if a person has AIDS and their immune system is compromised, the body is unable to fight off the herpes simplex virus and they become infected with the herpes virus. Also, once infected, these people can be more severely affected by complications from the herpes virus than an otherwise healthy person. This is why herpes simplex is an opportunistic disease. It can also infect people with weak immune systems due to reasons other than AIDS, including newborns or people who have undergone major surgery.