User blog comment:Omega natsu2/Episode 201: Delivery, Review./@comment-4449950-20140927033705/@comment-7418318-20140928205110

F-Rogue and F-Lucy just went through once. The Spirits on the other hand came into skin-to-gate contact once when closing it and then probably again when Lucy and Yukino tried to destroy it.

Then the keys were also put directly into the Gate to unlock it and if there was any "magical radiation" from the moment the Gate was destroyed, the keys were also right there to catch it.

So there was certainly enough opportunity to expose them to the more harmful components of the Gate's magic. Not to mention that the Gate was build partially with Celestial Spirit Magic, which might have contributed to something resonating/infecting/affecting the Spirits.

Then there's also the possibility that the Eclipse might have disrupted the veils seperating the different worlds and affected them in this way.