A two year old unimmunized child presents to a primary health centre with fever since 5 days. Mother also gives a history of rash staing behind ear-pinna a day before coming to OPD. On examination, child is having running nose and congested eyes. Most probable diagnosis is:-

**Core Concept**
The child's presentation with fever, rash behind the ear, and respiratory symptoms suggests a viral infection. The rash behind the ear, also known as the "cervical lymph node region," is a distinctive feature of certain viral illnesses.

**Why the Correct Answer is Right**
The combination of fever, rash, and respiratory symptoms in a two-year-old unimmunized child is highly suggestive of measles. Measles is a highly contagious viral illness caused by the measles virus (Morbillivirus), which spreads through respiratory droplets. The rash typically appears 3-5 days after the onset of fever and starts behind the ear, then spreads to other parts of the body. The child's unimmunized status increases the risk of measles infection.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because rubella (German measles) typically presents with a milder illness, and the rash usually appears on the face and spreads to the trunk, rather than starting behind the ear.

**Option B:** This option is incorrect because chickenpox (varicella) presents with a characteristic rash that starts on the trunk and spreads to other parts of the body, often accompanied by fever and headache.

**Option C:** This option is incorrect because diphtheria is a bacterial infection that typically presents with a respiratory illness, including a sore throat and cough, and is usually accompanied by a characteristic membrane on the tonsils.

**Clinical Pearl / High-Yield Fact**
The "three Cs" of measles are: cough, coryza (runny nose), and conjunctivitis (red eyes). These symptoms often precede the onset of the rash.

**Correct Answer:** C. Chickenpox (varicella)

✓ Correct Answer: C. Measles