## **Core Concept**
Yaws is a tropical disease caused by a specific bacterial infection. It primarily affects the skin, bones, and joints. The causative agent belongs to the genus *Treponema*, which also includes the bacteria causing syphilis.

## **Why the Correct Answer is Right**
The correct answer, *Treponema pallidum* subspecies *pertenue*, is the causative agent of Yaws. This bacterium is a spirochete, similar to the one causing syphilis, but it leads to a distinct clinical condition known as Yaws or Frambesia. The infection typically enters the body through cuts or abrasions in the skin, leading to a primary cutaneous lesion known as a "mother yaw." The bacteria then disseminate through the bloodstream, causing secondary lesions and potential long-term damage if left untreated.

## **Why Each Wrong Option is Incorrect**
- **Option A:** *Leishmania donovani* is incorrect because it causes visceral leishmaniasis or kala-azar, a completely different disease involving parasitic protozoa.
- **Option B:** *Mycobacterium leprae* is incorrect because it causes leprosy, a chronic bacterial infection primarily affecting the skin, nerves, and mucous membranes.
- **Option D:** *Bordetella pertussis* is incorrect because it causes whooping cough or pertussis, a highly contagious respiratory tract infection.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that Yaws is one of the endemic treponematoses, along with Bejel (caused by *Treponema pallidum* endemicum) and Pinta (caused by *Treponema carateum*). These diseases are distinct from syphilis but share a similar causative agent.

## **Correct Answer:** C. *Treponema pallidum* subspecies *pertenue*.