Mind control sexually transmitted virus scenario:
One day, doctors and and health care professionals began noticing a sudden rise in sexual problems between couples. But this time, it's not due to the lack of sex but it's due to couples can't get enough of it and this affects their daily lives negatively. Police were also out of hands handling reports of adultery and sex in public places.
Later on, scientist discovered a completely new strain of virus without any familial connection to any known virus on the earth in these affected people. This strain apparently hijacks a human carrier's brain and raises his/her lust through the roof in order to achieve its objective to spread. Sex sessions between two carriers are often fatal if one or both have heart problems because they just grind endlessly till they are exhausted and collapse. Another thing is especially mind boggling - that the carriers don't have any negative symptom beside the uncontrollable lust. This could be the start of a nightmare - that the virus could very well also trick the human's immune system to make it not consider the thing as a threat!
Rumor has it that a scientist has found a way to end this catastrophe. Meanwhile, a new global sex cult is surfacing. They are trying to find him and end his life.