**Core Concept**
The question is testing the understanding of the indicators of an effective leprosy control program, which is a crucial aspect of public health and tropical medicine. Leprosy, also known as Hansen's disease, is a chronic bacterial infection caused by *Mycobacterium leprae*. Effective control of leprosy requires a combination of early detection, multidrug therapy, and public health measures.

**Why the Correct Answer is Right**
An effective leprosy control program can be indicated by a steady decline in the annual incidence rate, a high percentage of new cases being detected at the paucibacillary stage (i.e., with fewer than five skin lesions), and a high percentage of new cases being treated with multidrug therapy (MDT). This is because these indicators suggest that the program is able to detect cases early, prevent the spread of the disease, and provide effective treatment.

**Why Each Wrong Option is Incorrect**
**Option A:** Incidence of leprosy is increasing in the region. This is incorrect because an effective leprosy control program would be characterized by a decrease in incidence, not an increase.

**Option B:** High percentage of new cases being detected at the multibacillary stage (i.e., with five or more skin lesions). This is incorrect because an effective program would aim to detect cases early, at the paucibacillary stage, to prevent the spread of the disease.

**Option C:** Low percentage of new cases being treated with multidrug therapy (MDT). This is incorrect because an effective program would ensure that a high percentage of new cases are treated with MDT, which is the recommended treatment for leprosy.

**Clinical Pearl / High-Yield Fact**
One important aspect of leprosy control is early detection and treatment, particularly in the paucibacillary stage. This can prevent the spread of the disease and reduce the risk of disability and deformity.

**Correct Answer:** D.