**Core Concept**
The plague is a zoonotic infection caused by Yersinia pestis, transmitted primarily through the bites of infected fleas or direct contact with infected animals, leading to a range of clinical manifestations from bubonic to pneumonic plague.

**Why the Correct Answer is Right**
The plague is characterized by its distinct clinical presentations, including bubonic plague, where patients develop swollen lymph nodes or "buboes," and pneumonic plague, which is a highly contagious respiratory form of the disease. Yersinia pestis, the causative agent, is a Gram-negative coccobacillus that invades the lymphatic system, leading to the characteristic buboes. The correct answer is related to the clinical manifestations of plague.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it contradicts the fact that the plague is caused by Yersinia pestis, a specific bacterium. The plague is not caused by a virus.
**Option B:** This option is incorrect because it is not a recognized form of the plague. The pneumonic and bubonic forms are well-documented manifestations of the disease.
**Option C:** This option is incorrect because it implies that the plague is primarily transmitted through contact with infected humans, which is not accurate. The primary mode of transmission is through the bites of infected fleas or direct contact with infected animals.

**Clinical Pearl / High-Yield Fact**
The plague is a notifiable disease, and prompt recognition and reporting are crucial for public health control. Healthcare providers should be aware of the clinical presentations and risk factors for plague, particularly in areas where the disease is endemic.

**Correct Answer: B. Pneumonic plague is a highly contagious respiratory form of the disease.**