Common cold is caused primarily by:
**Core Concept**
The common cold is a viral infection affecting the upper respiratory tract, primarily caused by rhinoviruses. These viruses trigger an inflammatory response, leading to the characteristic symptoms of runny nose, sneezing, and congestion.
**Why the Correct Answer is Right**
Rhinoviruses (RV) are the most common cause of the common cold, with over 160 serotypes identified. They infect the nasal epithelial cells, causing the release of pro-inflammatory cytokines and chemokines, which attract immune cells and lead to the characteristic symptoms. The RV viruses are transmitted through respiratory droplets, direct contact, or contaminated surfaces.
**Why Each Wrong Option is Incorrect**
* **Option A:** Adenoviruses can cause respiratory infections, including the common cold, but they are not the primary cause. They are more commonly associated with conjunctivitis and gastroenteritis.
* **Option B:** Coronaviruses can cause the common cold, but they are less common causes compared to rhinoviruses. They are more commonly associated with severe respiratory infections like COVID-19.
* **Option C:** Influenza viruses cause influenza, a different type of respiratory infection with distinct symptoms, such as fever, cough, and body aches.
**Clinical Pearl / High-Yield Fact**
Rhinoviruses are highly contagious and can be spread through respiratory droplets, direct contact, or contaminated surfaces. To prevent the spread of the common cold, it is essential to practice good hygiene, such as frequent handwashing and avoiding close contact with infected individuals.
**Correct Answer: D. Rhinoviruses**