herpes simplex
"I have been taking zovirax for over 12 years, 400 mg each night at bedtime.  I have only had a few outbreaks, caused by kissing my husband who had outbreaks.  On doctor's orders, I am to increase to 800 mg each night at bedtime when I do have an outbreak, or when I'm not feeling well.  Other virus' can set off a cold sore attack."