**Question:** Broncho-pneumonia due to measles occurs due to

A. Inhalation of measles virus particles
B. Infection of lung cells by measles virus
C. Spread of respiratory secretions containing measles virus
D. Infection of the respiratory tract and subsequent spread to the lungs

**Correct Answer:** D. Infection of the respiratory tract and subsequent spread to the lungs

**Core Concept:** Measles is a contagious viral illness caused by the measles virus, a member of the Morbillivirus family. The primary route of transmission is through respiratory droplets containing the virus when an infected person talks, coughs, or sneezes.

**Why the Correct Answer is Right:** Broncho-pneumonia occurs when the measles virus reaches the respiratory tract and infects the epithelial cells lining the airways and alveoli. This leads to inflammation and damage to the lungs, impairing gas exchange and causing symptoms such as cough, fever, and shortness of breath. The correct answer, D, explains that the infection of the respiratory tract is the initial event leading to the development of pneumonia due to measles.

**Why Each Wrong Option is Incorrect:**

A. Measles virus particles are too large to inhale and directly cause broncho-pneumonia. The virus primarily affects the respiratory tract, not the airways or alveoli.

B. Measles virus primarily affects the respiratory tract, not lung cells directly. Infecting the respiratory tract is the initial event leading to the development of pneumonia.

C. Inhalation of respiratory secretions containing measles virus is a secondary event after the respiratory tract has already been infected.

**Clinical Pearl:** Measles pneumonia is a potentially severe complication of the disease, leading to increased morbidity and mortality. Early diagnosis and supportive treatment are crucial to improve patient outcomes.