Disease of the soul (Based off of Disease of the mind.)

There is a disease for monsters that started right after the barrier opened. Where monsters will become savage giant beasts, Humans aren't immune except the disease would kill them. The disease is spread through bite and scratch, And it's uncureable. But there is still a sliver of hope someone just needs to reach it.
Sans for some reason kept some of his thoughts in tact. For instance he doesn't care about spreading the disease just taking care of his still normal brother although it isn't easy. When Papyrus died Sans was so close to loosing it when Melody showed up. He had the actual intent to kill her when he froze...What's gonna happen next?