8 Year old boy presented with swelling on both sides of the face, below the ears of 4 days duration. It first started on the left side and then 3 days later on the right side Cause for the disease will be

**Core Concept**
The clinical presentation suggests an infection of the **parotid glands**, which are located on both sides of the face, below the ears. This condition is known as **parotitis**. The key concept being tested is the identification of the cause of parotitis, particularly in a pediatric patient.

**Why the Correct Answer is Right**
The most common cause of parotitis in children is **mumps**, a viral infection caused by the **mumps virus**. The virus affects the **salivary glands**, particularly the parotid glands, leading to swelling and inflammation. The fact that the swelling started on one side and then progressed to the other side is consistent with the typical presentation of mumps.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the description does not match a typical bacterial infection.
**Option B:** Incorrect as it is not a common cause of parotitis in children.
**Option C:** Incorrect because it is not a known cause of parotitis.

**Clinical Pearl / High-Yield Fact**
Mumps is a highly contagious viral infection, and the diagnosis is often made clinically based on the presentation of parotid gland swelling. Vaccination against mumps is available and is part of the standard childhood immunization schedule.

**Correct Answer:** D. Mumps virus

✓ Correct Answer: C. Paramyxo virus