**Core Concept**
Scrub typhus is an infectious disease caused by the bacterium *Orientia tsutsugamushi*, transmitted through the bite of infected chiggers. The disease is characterized by a distinctive eschar at the bite site, followed by fever, headache, and body aches.

**Why the Correct Answer is Right**
The correct answer is related to the transmission and clinical presentation of scrub typhus. *Orientia tsutsugamushi* is transmitted to humans through the bite of infected chiggers, which are larvae of trombiculid mites. The bacterium multiplies in the salivary glands of the chigger and is transmitted to humans during feeding.

**Why Each Wrong Option is Incorrect**
**Option A:**
**Option B:**
**Option C:**
**Option D:**

**Clinical Pearl / High-Yield Fact**
A key clinical feature of scrub typhus is the presence of an eschar at the bite site, which is a dark, scab-like region that forms at the site of the chigger bite.

**Correct Answer:** D. Orientia tsutsugamushi