**Core Concept**
Spirillary rat bite fever is a rare zoonotic infection caused by *Spirillum minus*, transmitted through bites from infected rodents. The disease is characterized by a unique clinical presentation and distinct laboratory features.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of spirillary rat bite fever, which involves the formation of a characteristic lesion at the site of the rat bite. This lesion is known as an eschar, a necrotic area that develops into a black scab. The eschar is a hallmark of spirillary rat bite fever, distinguishing it from other types of rat bite fever.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the presence of a lymphangitis is not a specific feature of spirillary rat bite fever. While lymphangitis can be present in some cases, it is not a distinguishing characteristic of this disease.

**Option B:** This option is incorrect because the presence of a rash is not a specific feature of spirillary rat bite fever. While a rash may be present in some cases, it is not a distinguishing characteristic of this disease.

**Option C:** This option is incorrect because the presence of a fever is a non-specific symptom that can be present in many different infections, including spirillary rat bite fever. However, fever alone is not a distinguishing characteristic of this disease.

**Clinical Pearl / High-Yield Fact**
* Spirillary rat bite fever should be considered in the differential diagnosis of patients who present with a characteristic eschar at the site of a rat bite.

**Correct Answer: D. Eschar formation at the site of the rat bite.**