I've seen news reports about rats monkeys and pigs that were geneticly engineered to have the glow in the dark gene from an algi(spelling?). could a virus aquire that gene from those specimens and end up crossing the species barrier and infecting humans with the green glow genes? I believe it woulnd be extremellly hard to have the virus cross the barrier, since viruses have crossed from species much more distant to humans (bird flu for example), pigs rats and monkeys have been used in researches because from their similarities in many aspects to humans, so i believe a virus comming from the would have relative easyness when trying to infect humans, but I might be wrong...
Re: human firefly virus on the wild
Try the links in the MadSci Library for more information on Genetics.