## **Core Concept**
The question assesses understanding of indicators for an effective leprosy control programme. Leprosy, also known as Hansen's disease, is a chronic infection caused by *Mycobacterium leprae*. Effective control programmes aim to detect and treat cases early to prevent disability and reduce transmission.

## **Why the Correct Answer is Right**
An effective leprosy control programme is indicated by several key performance indicators, including a decrease in the number of new cases detected with deformity/ disability, a decrease in the number of new cases detected, and an increase in the proportion of cases detected with multibacillary leprosy (indicating more effective detection of all types of leprosy). A decrease in the detection of multibacillary cases could indicate a failure in detecting cases, especially the more severe forms.

## **Why Each Wrong Option is Incorrect**
- **Option A:** A decrease in the number of new cases detected with deformity/disability is a good indicator of an effective leprosy control programme. Early detection and treatment prevent disabilities.
- **Option B:** A decrease in the number of new cases detected could indicate effective control measures but must be interpreted with caution, as it could also reflect under-detection.
- **Option D:** An increase in the proportion of cases detected with multibacillary leprosy could indicate improved detection efforts, as it suggests that more cases, including the more severe forms, are being identified.

## **Why Option C is Incorrect (Correct Answer)**
- **Option C:** A decrease in the detection of multibacillary cases might suggest that the programme is missing cases, particularly the more severe and infectious multibacillary forms. This would not indicate an effective control programme.

## **Clinical Pearl / High-Yield Fact**
A key indicator of an effective leprosy control programme is the **"Detection of new cases with disability"**, as it reflects both the programme's ability to detect cases early and the overall burden of disease in the community.

## **Correct Answer:** . Decrease in detection of multibacillary cases.