Jarisch-Herxheimer reaction

noun

Ja·​risch-Herx·​hei·​mer reaction ˈyä-rish-ˈherks-ˌhī-mər- 

: an increase in the symptoms of a spirochetal disease (as syphilis, Lyme disease, or relapsing fever) occurring in some persons when treatment with spirocheticidal drugs is started

called also Herxheimer reaction