In the movie District 9, Wikus van der Merwe goes through a transformation into an alien after being exposed to an alien artifact. Throughout the development of the story, it is revealed that the artifact contains a type of fuel needed to operate the alien ship.
When Wikus first discovered the artifact, he tried to open it. Some of the contents was expelled (looked like it may be under pressure) into his face, triggering the transformation.
Was the substance that triggered the transformation, and the fuel collected by the alien Christopher the same thing? In addition, given the potent nature of the substance that affected Wikus, would he not have been spreading it to everyone he came into contact with?