**Core Concept:**
Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis, which predominantly affects the lungs but can also affect other organs. Multi Drug Resistant TB (MDR-TB) is a form of TB that is resistant to two key antibiotics: isoniazid and rifampicin. The World Health Organization (WHO) provides regular updates and reports on TB burden worldwide.

**Why the Correct Answer is Right:**
The correct answer, **India**, accounts for over 60% of the world's Multi Drug Resistant TB cases. India has one of the highest TB burdens globally, with a high prevalence of MDR-TB due to factors like poor treatment compliance, inadequate diagnosis, and inadequate drug supply.

**Why Each Wrong Option is Incorrect:**
A. **China**: While China has a considerable TB burden, it does not account for over 60% of MDR-TB cases worldwide.
B. **USA**: The United States has a low TB incidence and a low MDR-TB prevalence, making it an unlikely choice.
C. **Nigeria**: Nigeria has a significant TB burden, but it is not the country responsible for over 60% of global MDR-TB cases.

**Why Each Wrong Option is Incorrect:**
D. **Russia**: Although TB and MDR-TB are prevalent in Russia, it does not account for over 60% of the world's MDR-TB cases.

**Clinical Pearl:**
MDR-TB is a serious global health concern, and awareness of its prevalence and contributing factors is crucial for healthcare professionals working in TB control and treatment programs. Improving prevention, diagnosis, and treatment strategies can help combat MDR-TB and reduce its impact on public health globally.