My understanding is say w/ HIV there are different strands. Say one partner has a strain of HIV A...and their partner has HIV B. If they have unprotected sex and pass along the HIV...they could now both have a strain HIV AB.
They were probably on a certain medicine regiment or "cocktail" they call them. The meds that WERE working to combat their own virus might stop working now that they have strain HIV AB.
If one of these partners has unprotected sex w/ another partner who has HIV C...now they've created an HIV ABC. This is one reason this disease is so hard to fight b/c it is constantly mutating.
I do not know if this theory happens w/ other STDs like Gonorrhea, Herpes, etc.
I am sure one of our Drs can explain more and correct any misunderstandings on my part.
