relapsing : Idioms & Phrases

• noun marked by recurring high fever and transmitted by the bite of infected lice or ticks; characterized by episodes of high fever and chills and headache and muscle pain and nausea that recur every week or ten days for several months
  recurrent fever.
  

WordNet

• (Med.), an acute, epidemic, contagious fever, which prevails also endemically in Ireland, Russia, and some other regions. It is marked by one or two remissions of the fever, by articular and muscular pains, and by the presence, during the paroxism of spiral bacterium (Spirochæte) in the blood. It is not usually fatal. Called also famine fever, and recurring fever.

Webster 1913