Cool game. The idea in itself fits the theme well (reminds me of that game back on old Windows systems, where you play a spider trying to trap a snake), and the art/audio complements it really well.
The single player is quite hard. It either needs careful planning or is unbeatable as of now.
I tried playing multiplayer on my own as well, but it's impossible to independently coordinate both players. If I press "A" for one, I automatically end up pressing the left arrow button for the other as well xD Anyway, I think you intended it to be Vs, but it looks like it could be a cool CoOp-MP, since for example blue colored diseases erase the green player, so blue should be helping out green and vice versa to keep both diseases in check.
Overall a good entry, just a bit too difficult to beat.