How does influenza affect the body?

Influenza, commonly known as the flu, is a highly contagious respiratory illness caused by influenza viruses. It affects the respiratory system, particularly the nose, throat, and lungs. Here's an overview of how influenza impacts the body:

1. Infection and Replication:

- Influenza viruses enter the body through the mouth or nose.

- The virus binds to receptors on the surface of respiratory tract cells and gains entry.

- Once inside the cells, the virus starts replicating rapidly, producing numerous new viral particles.

2. Tissue Damage:

- As the virus replicates within the cells, it damages the lining of the respiratory tract, including the cells lining the鼻咽。

- This damage leads to inflammation and destruction of the affected tissues, resulting in the typical symptoms of the flu, such as a runny nose, sore throat, and cough.

3. Release of Pro-inflammatory Cytokines:

- In response to the viral infection, the body's immune system releases pro-inflammatory cytokines, such as interleukin-1, interleukin-6, and tumor necrosis factor-alpha.

- These cytokines trigger systemic inflammation, causing symptoms like fever, chills, muscle aches, fatigue, and loss of appetite.

- In severe cases, excessive inflammation can lead to complications such as pneumonia and acute respiratory distress syndrome (ARDS).

4. Weakened Immune System:

- Influenza infection can temporarily weaken the immune system, making individuals more susceptible to secondary bacterial infections, such as pneumonia or ear infections.

5. Respiratory Complications:

- In certain individuals, influenza can cause severe respiratory complications, particularly in people with underlying medical conditions, the elderly, and young children.

- Severe illness may require hospitalization or intensive care with mechanical ventilation.

6. Viral Shedding:

- Infected individuals can transmit the virus to others from 1-2 days before symptoms appear until several days after the symptoms have resolved.

- The duration of viral shedding varies from person to person.

Influenza typically lasts for about 2-7 days, with symptoms gradually improving over time. However, some individuals may experience more severe illness, requiring medical attention or leading to complications.