Relapsing fever is an acute bacterial infectious disease caused by spirochaetes transmitted through bloodsucking insects (lice, ticks) and characterized by periodic paroxysms of fever. The attack terminates after 3 to 10 days. After 1 to 2 weeks a somewhat milder relapse occurs. Recovery eventually occurs after the person develops immunity by experiencing 3-10 relapses. The overall mortality rate for relapsing fever is very low. With treatment, the initial attack is modified and relapses are prevented or reduced in number. Man is the only sufferer of epidemic (louse-borne) relapsing fever; both man and animals suffer from endemic (tick-borne) relapsing fever.
Epidemic relapsing fever occurs mainly in countries with poor cultural and economic development; endemic relapsing fever is found an all the continents.