The non-specific super-fungi Deadlius Diseasus is spreading throughout the world. Actually, this disease is badly named: it doesn't kill anybody - it just infects them, then after a period of ~1 week, starts causing euphoria. In a big way. So much so that anybody infected with the disease is utterly demotivated to do anything other than laze around all day, because nothing can bring them greater happiness than they are currently experiencing.
The disease is airborne. It transmits itself through microscopic and therefore invisible spores which are released from any and all bodily orifices in infected humans.
The UN has met and decided that this disease, once it has infected enough people, will cause the end of the human race because people are too apathetic to work and therefore food cannot be gathered.
However, the average person has no massive problem with the existence of this disease, because it has no bad effects (apart from massive laziness).
How can they stop the spread of this disease when most people are not motivated to stop themselves becoming infected?
The disease cannot live anywhere except for on humans, but the spores can lie dormant on objects for an extended period. People who are infected are so apathetic, they do nothing at all, even at risk to their own health.