**Core Concept:** Plague is a highly infectious bacterial disease caused by Yersinia pestis, which primarily affects humans and animals. It is transmitted through direct contact with infected organisms, flea bites, or contaminated food and water.

**Why the Correct Answer is Right:** Plague is primarily transmitted through direct contact with bodily fluids and secretions of infected mammals, such as rats, squirrels, and fleas. The most common mode of transmission is through direct contact with infected bodily fluids, like blood, pus, or saliva. In this case, the correct answer is **D** because it refers to contact transmission, which is a primary mode of plague transmission.

**Why Each Wrong Option is Incorrect:**

A. Flea bites are a secondary mode of transmission for plague, not the primary mode. Flea transmission occurs when a flea feeds on an infected animal and then bites a human, injecting Yersinia pestis into the human body.

B. Plague is not transmitted through airborne droplets like tuberculosis, which is why this option is incorrect.

C. Plague does not primarily spread through ingestion of contaminated food and water, unlike cholera, which is why this option is incorrect.

**Clinical Pearl:** While plague is a rare disease in developed countries, it continues to be a significant public health concern in some developing nations. Early diagnosis and prompt treatment with antibiotics can lead to successful outcomes.

**Correct Answer:** D. Direct contact with infected bodily fluids or secretions.