Baby ferrets bought at the pet store seem to be responsible for many of these cases. Also, the simple act of holding an infected ferret then going home to your ferret can infect your ferret. There is no medicine or drug that will treat ECE directly. Many vets will prescribe antibiotics to control any secondary infections made possible by the ferret's stressed immune system. ECE has only recently been positively determined to be viral in origin, and as such, antibiotics will have no effect on the virus.
Treatment is simply supportive in nature.
The ferret MUST eat and drink. If it won't eat on its own, then it must be force fed both food and water. A ferret will die from dehydration long before it starves to death, and diarrhea causes severe dehydration, so fluids are essential. It can't be stressed enough that your ferret has to eat and drink, no matter how much it doesn't feel like doing so. Feed at least 4 times a day, more if the ferret can only be made to eat small amounts.