Something is very weird, but it looks totally unrelated to terrorism. It's actually probably quite exciting for the scientists, they might even discover a new disease!
The symptoms flares up only when the students are in the school itself, which means something in the school is triggering the symptoms.
It could be that bacteria or fungi or virus particles are all over the school, being spread by something inside it, but that they have very low survival capabilities after they start attacking someone. In that case, the disease (or whatever it is) would not leave the school, and would die out after the scientists go to work.
It could be that some sort of agent like bacteria or a fungus is producing some nasty chemicals, which cause a rash in some of the students.
It doesn't seem like it would be any kind of dangerous disease or virus, because it isn't really hurting anyone and it isn't spreading outside of the school. I wouldn't get worried about it.
Another possibility, Pittariasis Rosea, is something my son just had. It's viral and not serious. Bumps and a certain degree of itchiness. It lasts several weeks. He lives in Virginia.