兩大類: Louse-borne (LBRF, B. recurrentis) — refugee/poverty, epidemic high mortality; Tick-borne (TBRF, multiple Borrelia) — Western USA, cave/cabin exposure; 多次 fever-afebrile cycles 因 antigenic variation; doxycycline / ceftriaxone treat; Jarisch-Herxheimer 強烈。