Infection can be a cause of fever, but fever with no apparent reason can be an indicator of any cancer. In the Blood-related cancers like CLL, people tend to suffer more from unexplained fever. Fever of an unidentified basis is of greater than 101 degrees and persists more than three weeks without even one clear clarification.
Fevers linked with chronic lymphocytic leukemia can have several probable reasons, including underlying infections. In some conditions, the cancerous cells cause the brain to release such substances that can increase the body temperature.