This would make for an interesting scifi plot. A global virus spreads that has multiple parts and people must limit their contact with specific people or risk acquiring components that activate the parts of the virus they carry.
That episode of STNG is about a virus which targets a specific DNA.
> In sickbay, Crusher reveals to Riker that Volnoth was killed by a microvirus. The interesting part was that the microvirus was specifically designed for a certain strain of DNA in Acamarians, approximately one in a million. Riker notes that this is unnatural, which leads Crusher to presume that Volnoth was murdered.
In one of Greg Egan's short stories there is a religious maniac who engineers a deadly STD so as to permit only one lifetime sexual partner, lest the virus be activated and kill the fornicator. (If I remember the plot correctly. It's in the "Axiomatic" short story collection.)
