Hepatitis C Risk –Transmitted via blood-to-blood contact, this illness is harder to acquire from sexual contact. While there is little evidence proving Hepatitis C acquisition through oral sex, a theoretical risk exists if there is any blood present in the giver and receiver. Thus, a risk of transmitting Hepatitis C via cunnilingus, fellatio or analingus exists if there is any menstrual blood, bleeding gums, a throat infection, cold sores, canker sores, genital warts, hemorrhoids or any other breaks in the skin in any involved body structure – vagina, clitoris, labia, penis, testicles, anus, perineum, lips, tongue or anywhere else on the genitalia or inside the mouth.
Experts believe that viral hepatitis is more likely to be transmitted if either the positive or the negative partner has another STD, especially one that causes sores or lesions. Thus, suspicious symptoms should always be checked by a doctor before engaging in oral sex.
http://www.hepatitiscentral.com/mt/archives/2009/10/can_you_get_vir.html