An overview of tick-borne relapsing fever with emphasis on outbreaks in Texas.

Tick-borne relapsing fever (TBRF), a disease of humans and other animals, has been recognized in North America since early in this century. Caused by Borrelia spirochetes, TBRF is transmitted by softshelled Ornithodoros ticks, which may also act as reservoirs for the etiologic agents. Initial symptoms include sudden onset of fever, chills, headache, arthralgias, and myalgias. Persons with TBRF may suffer several febrile episodes or relapses unless they are diagnosed and treated promptly because TBRF spirochetes are able to alter their outer surface proteins and, thus, escape the infected host's immune response. Laboratory diagnosis is made by detecting spirochetes in peripheral blood specimens or by inoculating laboratory mice with blood collected during febrile episodes. In the 1930s and '40s, TBRF was reported commonly in Texas. More recently, fewer cases have been reported, although 13 cases were confirmed between 1990 and the first half of 1994.