How is a fistula generally treated?

Depends on the cause: Fistulae caused by Crohn's disease can be treated with medications such as remcade. Others often require surgery or occasionally can be treated by injection with fibrin glue.

Depends: What fistula are you referring to. There can be a fistula in the abdomen or in the peri anal area. Abdominal fistulas are lot more complex to treat. Anal fistulas are of several types and treatment ranges from a simple division of a fistula tract to having a colostomy or a drain and requiring multiple procedures.