My cat is about a year old. He has been vaccinated, dewormed, etc.

He was recently exposed to a large number of other cats at a shelter.

For the past couple days, he has been sneezing. Then today, he stopped sneezing, but he is listless with a runny nose and is not eating or drinking. He feels as though he has a fever. He's been sleeping all day.

So far, all we've done is use a dropper to feed him water (assuming he'll dehydrate).

First, what is likely the illness. Second, what can we do to help him?

Thanks,

Bill & Lyuda