They called it the QBE virus. Short for Quintessence Bifurcation Enhancement, it was so named because the scientist that discovered it fancied himself a bit of a poet... But also because it seemed to separate humanity into two separate evolutionary paths. The public quickly picked up on the fact it sounded very much like "Cubi", from the mythological "succubus" demon , made famous by religions and, of course, popular culture (ie. Porn).
It was a strange, almost miraculous affliction, with an impressive - some would say worrying - ability to adapt and overcome any and all antiviral treatments. In fact, there has yet to be a cure of any kind developed for the virus. Some people believe that the reason there is currently no cure is because nobody WANTS to find a cure. After all, it has turned out to have numerous, often beneficial effects.
The first effect is simple, yet with far-reaching consequences. The body of the carrier becomes... more efficient. Neural signals are sent and interpreted faster, muscles and organs process oxygen and energy quicker and with fewer losses. The entire digestive tract become so good at wringing energy and useful nutrients from food that, in most cases, there is no longer any need to urinate or excrete at all.
Another side effect is that the body becomes more youthful in appearance; wrinkles and scars fade and disappear, eyesight becomes 20/20 or better, joints regain their range of motion and aches and pains become a thing of the past. Flexibility and elasticity go through the roof, not to mention healing in general is sped up dramatically.
With all these positive effects, one might ask why the public would be so divided to the point it resembles racism... The answer would be the secondary effects of the virus. As one might have guessed from the nickname given to it, the virus also significantly enhances and alters the sexual characteristics of its carriers. These changes vary from person to person, but often include such things as penis, testicle and breast growth, hermaphroditism, increased semen and/or milk production, as well as most commonly an extremely heightened libido, often to the point of addiction. 
The virus seems to -feed- on sexual fluids, creating withdrawal symptoms more extreme than any known drug, resulting in the deaths of hundreds of not thousands of victims who were 'starved' either by their own beliefs, or that of those around them. To facilitate and encourage the act of intercourse, carriers of the virus are capable of producing extremely potent pheromones that act as universal aphrodisiacs; they seem to have a much more pronounced effect on those who are not currently infected, perhaps to aid in the spread of the virus.
These combined effects create what some people call a "growing legion of sex-crazed deviants" and unfortunately the issues didn't stop there...
The virus was transmittable through sexual fluid transfer, blood and, most regrettably, it was hereditary. This meant that not only could children catch this virus, but it could be passed on to newborn children. The only saving grace was that the virus remained in its incubation stage until 4 years of age, but after that... The children would also require a regular, and rather specific, diet. Some were fortunate enough to be able to survive only on breast milk, while others were... not so lucky. It was a very uncomfortable situation for a lot of people.
Over the years, as more knowledge was accumulated about the virus and it's effects, it was gradually incorporated into society in a variety of ways. Special gated communities were created, advertised as safe spaces for those infected (who often liked to forgo clothing) but they also served as a way to keep the carriers away from those who didn't wish to be exposed or infected. Government assistance and incentives were provided, though everything was very meticulously documented and specially trained security forces were always on standby.
These communities grew, flourished and thrived, which frustrated those who vilified their lifestyle, but crime levels and violence were at an all time low - practically a utopian society.