Relapsing fever is characterized by recurring episodes of fever and septicemia s

Relapsing fever is caused by Borrelia recurrentis. This bacterium continually changes its antigenic surface components throughout its life cycle in its human host. Because the body's defense is to create antibodies directed against these surface molecules, some bacteria with surface antigens different from the antigens being targeted by the immune response manage to evade the immune system. These surviving spirochetes go on to multiply and cause a relapse of the fever. This cycle continues, with a few changed spirochetes evading the system each time and causing the next round of the disease.