Why Do you think Ivan has such a high fever?
I think he hasn't been well fed and is not healthy. Since he is in a prison, he must not get the nutrients his body needs to survive. According to BrightHub.com, the five things that humans need to survive are oxygen, water, food, shelter and sleep. Clearly, Ivan is not getting most of these things and he is having I think he hasn't been well fed and is not healthy.
How did Ivan get there?
It is not known how he got too this prison, but he must have committed some sort of crime, (unfair or fair) he is in prison now. He might have had different beliefs which made him go into this place, likely against communism.
I believe that this book has not shown much yet. From the chapters I've read the book seems a little boring and paces slowly. I have no predictions of what will happen