You are applying for the same job! Or um GM...thingit...not really a job since you won't be paid and all that. =P
Okay, so I'm going to build upon your idea Lirliel, even though it might not totally sound like it. You gave me an idea, more or less. But first I want to just say that the source of it doesn't really matter to me, by the time it reaches Felicity and Sydney it's rapey zombies looking to infect everyone.
My idea is something more along the lines of Interpol and/or the US gov't wanting to test the viability of a biological attack from terrorists. How it would spread and how quickly it could decimate the world. The idea, like you said, is either to give them a small rash or else to just give them a radioactive isotope that lets satellites see them, but is otherwise totally harmless. Their computer models are saying that either the person that's carrying it, if by touch or bodily fluids, will die in a couple of days, or the world will effectively end within a week...and everything between. So they have to run their real-life experiments with a harmless agent in order to find out the real result.
They find out pretty much what they feared. They "infect" a random person at a major airport (JFK, LAX, Atlanta) and they touch so many people even by accident that by the time that person gets home the isotope is showing up across the country, then a few hours after that across the world as planes land and take off again. The world would effectively be infected after a few days.
Now either the isotope hits someone that just had a new experimental treatment and turns them into basically a sex machine, never being able to get enough, and finally they rape someone. It's horrible but basically goes unnoticed by the police. Why? Because the woman (or man) is too ashamed to come forward. By the time they notice anything is wrong with them it's too late, they're arousal is through the roof, they can't think, they essentially become brain-dead but can still walk around and rape. For whatever reason having sex with another living person staves off the new "infection" for a few days until they need to do it again. At first it presents itself as a serial rapist. Normally this wouldn't be a big deal, but it seems like "patient zero" seems to be able to return to relatively normal functions after rape for the first few days of his/her infection. They travel a lot for business so it happens again and again, infecting more and more slowly, but with each one infected they then infect three to five (or more) more people, and then those infect that many more.
I figure the isotope gets destroyed after it mutates patient zero, so that the gov't doesn't really see what's up. By the time anyone realizes what's going on, there are hundreds if not thousands infected all over the world. And police forces would sooner try to arrest them than shoot them dead, especially not shoot them in the head. So then they get infected, society starts to break down, and everything really just goes to shit. Now we were thinking that the zombies might have higher-than-normal strength making it all the more difficult to fight them.
Martial Law could be mandated as national guard troops swoop in, they try to quarantine the place but all it takes is one member to get pulled away and raped then they get back into camp and the infection continues to spread. We could say it's some kind of mutated symbiotic virus or bacteria or something. I really see it as only being transmitted through sex, not through blood or anything like that, just to keep the game on track of having rape-type zombies rather than flesh-eating or whatever other kinds there are.
The other option would be that someone injects patient zero, or otherwise infects them with this symbiotic infection and it grows from there. So perhaps at Felicity's and Sydney's college one infected either rapes or has sex with someone else. By this time it's mutating people within seconds of the rape, so one guy rapes a girl, then he rapes another girl, but by that time the first girl has raped a guy...anyway by the time all is said and done before the cops can even be called a quarter of the campus would be infected, then by the time the cops got there half, they'd get overrun pretty quickly and raped themselves, and then the whole city would be infected just from the campus.
I hope that makes sense...and that really did come from Lirliel's idea, honest!