**Core Concept**
The control of tuberculosis (TB) and leprosy relies on the implementation of public health measures, including the use of antibiotics and vaccines to prevent and treat these infectious diseases.

**Why the Correct Answer is Right**
TB and leprosy are both chronic infections caused by Mycobacterium tuberculosis and Mycobacterium leprae, respectively. Effective control of these diseases involves the use of antibiotics such as isoniazid, rifampicin, and dapsone, which target the bacterial cell wall and inhibit cell division. Additionally, BCG vaccine is used to prevent TB in high-risk populations, such as children and healthcare workers.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while chemotherapy is a crucial component of TB and leprosy control, it is not the only factor involved.
**Option B:** This option is incorrect because while the BCG vaccine is effective in preventing severe forms of TB, it does not provide complete protection against the disease.
**Option C:** This option is incorrect because while public health measures such as contact tracing and screening are important in controlling TB and leprosy, they are not the primary means of control.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the control of TB and leprosy requires a multi-faceted approach that includes the use of antibiotics, vaccines, and public health measures.

**Correct Answer: D. Chemotherapy. Chemotherapy is the primary means of controlling TB and leprosy.**