Does nanophage "Grey Goo" count as a disease if it infects a person and waits a while before rapidly consuming their boddy and everythig else in the area? Several sci-fi settings (and more than a few others) feature parasites that will slowly grow inside the host until they reach some new stage in their growth cycle, and then burst out to seek new victims, killing the host in the process? Also common, and a little more disease-like, are creatures that lay eggs on or in a host, and when the eggs hatch... *somehow, through sheer willpower, managaes to hold down her breakfast* ...though this usually isn't instantly fatal if the eggs are laid somewhere non-vital, like a limb.
I imagine that for Nekos and Yamataians, any kind of autoimmune syndrome would be very, very, very, very bad.
Another possibility might be femtomachines or HSCS nanomachines going haywire (or being caused to go haywire) and acting like "mad cow disease" prions, only affecting the entire body instead of just the brain and nervous system.
Can Yamataians/Nekos get computer viruses?