**Core Concept**
Jarisch-Herxheimer reaction is a transient, usually self-limiting, febrile reaction that occurs after the initiation of antibiotic therapy for certain bacterial infections, such as syphilis, Lyme disease, or yaws. It is caused by the release of endotoxins or other bacterial products from the dying bacterial cells.

**Why the Correct Answer is Right**
The Jarisch-Herxheimer reaction is thought to be triggered by the release of endotoxins, which stimulate the production of pro-inflammatory cytokines, leading to symptoms such as fever, headache, and malaise. This reaction is more common in infections caused by spirochetes, such as Treponema pallidum in syphilis, where the bacteria are highly susceptible to penicillin. The reaction typically occurs within 24 hours of starting antibiotic therapy and resolves on its own within 24-48 hours.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the Jarisch-Herxheimer reaction is not typically associated with viral infections, which do not produce endotoxins.
**Option B:** This option is incorrect because the reaction is not caused by the antibiotic itself, but rather by the release of bacterial products.
**Option C:** This option is incorrect because the reaction is not a specific response to penicillin, but rather a general response to the death of bacterial cells.

**Clinical Pearl / High-Yield Fact**
The Jarisch-Herxheimer reaction can be managed symptomatically with antipyretics and analgesics, but it does not affect the long-term efficacy of antibiotic therapy.

**Correct Answer:** C.