**Question:** Rotavirus is a double-stranded RNA virus with a double-walled capsid. Which one of the following statements best describes rotavirus?

A. Rotavirus is a single-stranded RNA virus with a single-walled capsid.
B. Rotavirus causes type 2 diabetes.
C. Rotavirus is a bacterium.
D. Rotavirus is associated with Alzheimer's disease.

**Correct Answer:**

**Core Concept:**
Rotavirus is a group of viruses that primarily infects the small intestine of various mammals, including humans. These viruses are known for causing severe diarrhoea, particularly in young children and immunocompromised individuals. Double-stranded RNA viruses have a distinctive double-stranded genetic material, while a double-walled capsid refers to the structure of the viral envelope surrounding the genetic material.

**Why the Correct Answer is Right:**
Rotavirus belongs to the Reoviridae family of viruses and is characterized by its double-stranded RNA genetic material enclosed within a double-walled capsid. This structure is unique to rotavirus and sets it apart from other viruses, such as single-stranded RNA viruses or those with a single-walled capsid. In this case, option A is correct because it specifically mentions the viral genetic material and capsid structure of rotavirus.

**Why Each Wrong Option is Incorrect:**
- Option B incorrectly associates rotavirus with type 2 diabetes, which is unrelated to the virus.
- Option C mistakenly claims rotavirus is a bacterium, which is not the case as it is a virus.
- Option D incorrectly links rotavirus to Alzheimer's disease, which is a neurodegenerative disorder caused by different factors, not rotavirus infection.

**Clinical Pearl:**
Understanding the distinctive characteristics of rotavirus, such as its double-stranded RNA genetic material and double-walled capsid, is crucial for identifying and diagnosing viral infections. This knowledge helps differentiate rotavirus from other viruses and bacterial pathogens causing diarrhoea.