The etiological agent for roseola infantum is –a) Parvovirusb) Human herpes virus 6c) EBVd) CMV

**Core Concept**
The question tests knowledge of the etiological agents responsible for specific infectious diseases, focusing on roseola infantum, a common illness in infants characterized by a high fever followed by a rash. **Roseola infantum**, also known as sixth disease, is primarily caused by a viral infection. Understanding the **virology** behind this condition is crucial for diagnosis and management.

**Why the Correct Answer is Right**
Human herpes virus 6 (HHV-6) is identified as the primary cause of roseola infantum. The virus leads to symptoms such as high fever, which typically lasts for 3 to 4 days, followed by the appearance of a rash once the fever resolves. **HHV-6** infects most children by the age of two, leading to this condition.

**Why Each Wrong Option is Incorrect**
**Option A:** Parvovirus is incorrect because it is associated with erythema infectiosum, or fifth disease, not roseola infantum.
**Option C:** EBV (Epstein-Barr Virus) is incorrect as it is primarily known for causing infectious mononucleosis.
**Option D:** CMV (Cytomegalovirus) is incorrect because, although it can cause disease in infants, it is not the primary agent of roseola infantum.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **HHV-6** infection is very common in early childhood and usually results in a self-limiting illness, but it can be severe in immunocompromised individuals.

**Correct Answer:** b. Human herpes virus 6