What is the primary cause of the Jarisch-Herxheimer reaction in patients receiving treatment for syphilis?

The Jarisch-Herxheimer reaction is primarily caused by the rapid lysis of spirochetes, particularly Treponema pallidum, which occurs after the administration of antibiotics for the treatment of syphilis. When these organisms are rapidly destroyed, the release of endotoxins and other bacterial components into the bloodstream leads to a systemic inflammatory response. This response can manifest as fever, chills, and other flu-like symptoms.

The reaction typically occurs within several hours of initiating treatment and is believed to result from a combination of an immune response to the influx of bacterial antigens, but the critical initial trigger is indeed the release of these components from the lysed spirochetes. While the increase in immune response and other factors might contribute to the symptoms seen in the Jarisch-Herxheimer reaction, the primary underlying mechanism is the abrupt release of substances due to rapid bacterial lysis. This understanding is crucial in clinical settings to reassure patients experiencing these reactions following treatment for syphilis.