Kinda looks like ringworm . That can be treated with medication from a vet. But honestly if it is I would just cull your colony and wash down all tacks with bleach and start over . It's highly contagious and will spread to all your rats and even you. Also if you don't know it's not actually a worm. It's a fungus. Why they call it ringworm I duno lol.
It could be mites. Again if it's mites you may as well start over. They are hard to get rid of and if you buy the stuff to treat your rats great, but you can't feed them to your snakes.
Or could just be an irritation.