STD even if vergin?

You mean "Virgin", STDs can be transmitted through oral contact, i.e kissing (Chlamidya, & herpes). Common amongst teenagers, which is running rampant in British sixthforms is glandular fever, so look out for that.
Therefore, even without sexual intercourse, it is still possible to contract one. In addition to this, sharing needles can transmit blood related diseases such as AIDs or HIV*. HIV can be latent, as a retrovirus, it can reversibly transcribed into double stranded DNA, which can be intergrated into the hosts chromosome by intergrase. This defies central dogma of DNA synthesis. Being intergrated, HIV enters the lysogenic phase, where under certain environmental stimuli, can be triggered into the lytic pathway. The fact that HIV is intergrated into the chromosome, means that the virus can spread via blood.

Yes, but I said that with vergin I intend a person that never had a sexual act, of any kind, with no one.

Yes certainly. You can get STDs from kissing, oral and anal. Though its much more likely with the latter than the former. But the question is what's the probability of getting STDs given that you're a virgin? Very, very low.

So let's suppose that a couple, a man and a woman do a test and they result negative to all the STD.
They start to have regular sex acts.

They can get the STD, because one of them contracted it from a place?

Thanks.

P.S Can't understand why my T9 convert virgin in vergin automatically

No, you can’t get an STD from someone who is STD free. But people do lie about their sexual history, so using a condom just in case is recommended unless you really trust someone or get tested.

Maybe if bobs and vegene were involved.