Cryptosporodium is a nasty protozoan gut parasite which infects many species- and crosses between species too- you can catch it from pets so do be extra cautious woth hygiene especially if you have children around.
Unfortunately thete really are no effective treatments, not for humans or pets, so I'm afraid its a case of hanging in there with subcutaneous fluids, probiotics and recovery food, and hoping for the best
It is one of those things that unfortunately really gets a hold on stressed and immunocompromised baby animals from poor breeding facilities, especially if there is cross-sprcies contamination like perhaps in a pet shop breeder situation.
I'm sorry I cant give more positive news here but it is very often fatal for small animals and very serious even in small children. All you can do is provide supportive care. Best of luck x