You remove a tick from an individual by grasping it by the head. four days later, the individual develops a bull's eye around the bite and complains of fever and body aches. what is the likely cause?

The cause is a tick-borne disease,

According to the symptoms, its certainly a Lyme disease.

The bullseye (also called erythema migrans) around a tick bite leads to a bacterial infection: Borrelia burgdorferi.

Concerning the tick, it's from the genus Ixodes.