Saliva and stomach acids kill the viruses and other pathogens that concern you. The only concern that has clinical evidence of a chance for infection is contact with the mouth and throat. This has only been shown to be a risk when there are open sores of some type or what is referred to as "mico-abrasions".
I read once where a doctor recommended that women (or men I guess) use mouthwash before a date where CIM will happen instead of brushing their teeth. The reason... it's possible that the brushing action can cause microscopic abrasions in the mouth that can increase risks, but switching to mouthwash use or waiting an hour or two will allow the abrasions to close.
Also, here is something interesting reported by Associated Press and CNN.
(AP) Women who perform the act of fellatio and swallow semen on a regular basis, one to two times a week, may reduce their risk of breast cancer by up to 40 percent, a North Carolina State University study found.
Don't believe me? You can read it yourself here:
http://tatom.org/documents/CNN.com-S...studyshows.htm