“The reaction was first seen following treatment in early and later stages of syphilis treated with Salvarsan, mercury, or antibiotics. Jarisch thought that the reaction was caused by a toxin released from the dying spirochetes.” WKPD
“It is an acute, transient, febrile reaction that occurs within the first few hours after treatment for syphilis. The condition peaks at 6–8 hours and disappears within 12–24 hours after therapy. The temperature elevation is usually low grade, and there is often associated myalgia, headache, and malaise. It is usually of no clinical significance and may be treated with salicylates in most cases. The pathogenesis of the reaction is unclear, but it may be due to the liberation of antigens from the spirochetes.” ABFM
Reference
Am Fam Physician 2012;86(5):433-440.