Kim, we had the same thing when our RB Naomi came to live with us. Vasea got the virus from her, although she looked perfectly healthy. We had to administer some shots and give him some pills. I was also VEEEEEERY scared. But he got well in a few days.
We even had a hilarius situation when he escaped from my brother's hands and started running through all the apt with the needle and syringe in his rear end That made us take it easier. If he was able to run like that, that meant he can get well.

I hope you will remember it one day just like a minor problem.
And, don't give up with the good work you're doing for all those cats.