Two of my New York City fosters had ringworm. I was able to keep it from spreading. My vet prescribed Program off label (there is strong evidence that high dose Program works for ringworm) and Trezaderm for the sores. Both of these have low toxicity (I asked about that since they were kittens at the time.) It took about 6 weeks for it to go away.

It's a royal pain in the tush, but not very dangerous.