It is very rare to contract an STD from receiving fellatio. Plus, if she's a Virgin, your chances are pretty much non existent. However, good hygiene should be a criterion for oral pleasure, just saying :)
this is not the doctor sforum - you need to pay to post there.
if she's a virgin, it's very unlikely she has a std though she could have one orally. Unless you get obvious symptoms, not really worth any testing for.
www.ashastd.org has terrific info on all std's for more reading.
grace