The most common etiological agent for acute bronchiolotis in infancy is: March 2011
**Core Concept**
Acute bronchiolitis in infancy is a common lower respiratory tract infection characterized by inflammation and obstruction of the small airways. The etiology of bronchiolitis is multifactorial, but respiratory viruses play a significant role.
**Why the Correct Answer is Right**
The most common etiological agent for acute bronchiolitis in infancy is the respiratory syncytial virus (RSV). RSV is a single-stranded RNA virus that primarily infects the epithelial cells of the respiratory tract, leading to inflammation, edema, and necrosis of the bronchiolar epithelium. This results in the production of excess mucus and cellular debris, which obstructs the small airways and impairs gas exchange. The high viral load and rapid replication of RSV contribute to the severity of the disease.
**Why Each Wrong Option is Incorrect**
* **Option A:** Adenovirus is another common cause of respiratory infections in children, but it is less frequently associated with bronchiolitis compared to RSV.
* **Option B:** Parainfluenza virus can cause croup and other respiratory illnesses, but it is not the primary etiological agent for acute bronchiolitis.
* **Option D:** Influenza virus can cause respiratory illness, but it is not typically associated with bronchiolitis in infancy.
**Clinical Pearl / High-Yield Fact**
RSV infection can occur in all age groups, but the severity and frequency of the disease are highest in infants under 6 months of age. The first episode of RSV infection often occurs between 6 and 24 months of age, and subsequent infections can occur throughout childhood.
**Correct Answer:** A. RSV