I always don't get why would Shiro be able to make a plague. He was the envoy, his Shiro'Ken army makes sense but the plague, why? The Am Fah was able to control the plague, spread it and even control it to prevent further change from sickness. I don't see Shiro being a scientist. Also how did he make those monsters listen to him at all?
Even long after Shiro's death some Afflicted were further changing into monstrous size. It was also not explained.
Also the plague was more powerful than the Scarab one because it could affect even animals. But it was never properly explained. Is it magical? How does it spread? How did the Am Fah manage to control it?