**Question:** Pneumonia alba is due to -

A. Viral infection
B. Bacterial infection
C. Fungal infection
D. Parasitic infection

**Core Concept:** Pneumonia alba refers to a type of pneumonia characterized by a white, cloudy appearance on chest X-ray. This is often due to an overwhelming inflammatory response triggered by an infection, rather than a specific pathogen. The condition can be caused by various pathogens, including viruses, bacteria, fungi, and parasites.

**Why the Correct Answer is Right:** The correct answer, D (parasitic infection), refers to the possibility of pneumonia alba being caused by a parasitic infection, particularly by a protozoan like Histoplasma, Cryptococcus, or Pneumocystis. These organisms can lead to an excessive inflammatory response, resulting in the typical X-ray appearance of pneumonia alba.

**Why Each Wrong Option is Incorrect:**

A. Viral infection (Correct Answer D) is not the correct answer because pneumonia alba can also be caused by viral infections. Viral infections typically cause a milder inflammatory response, which is why it is not the most specific answer.

B. Bacterial infection (Option B) can also lead to pneumonia alba, but the presence of pneumonia alba does not always indicate a bacterial cause. A bacterial infection often results in a milder inflammatory response compared to parasitic or viral infections.

C. Fungal infection (Option C) can cause pneumonia alba due to the excessive inflammatory response triggered by the fungal infection. However, this option is less specific than parasitic infection and viral infection.

**Clinical Pearl:** Pneumonia alba is essential to recognize as it can indicate a severe inflammatory response rather than the presence of a specific pathogen. While viral and parasitic infections are more likely causes, bacterial infections can also lead to pneumonia alba. It is crucial to consider the clinical context, patient's history, and other radiological features to reach a precise diagnosis.