How does viruses cause disease in humans?

Viruses cause disease in humans by disrupting the normal function of cells. Viruses are not cells themselves, but rather are made up of a protein coat and a core of genetic material. When a virus infects a cell, it injects its genetic material into the cell's cytoplasm. This genetic material is then used to make new viral proteins, which are assembled into new viruses. The new viruses then leave the cell and can infect other cells.

The process of viral infection can cause damage to cells and tissues, leading to a variety of symptoms, including fever, chills, muscle aches, and fatigue. In some cases, viral infections can also lead to more serious complications, such as pneumonia, meningitis, and encephalitis.

Some of the most common ways that viruses cause disease in humans include:

* By damaging cell membranes. Some viruses, such as influenza virus, damage the cell membranes of infected cells. This damage can cause cells to leak fluid and proteins, which can lead to cell death.

* By disrupting cellular metabolism. Some viruses, such as HIV, disrupt the cellular metabolism of infected cells. This can interfere with the cell's ability to produce energy and make new proteins, leading to cell death.

* By inducing an immune response. Some viruses, such as measles virus, induce an immune response in infected cells. This immune response can lead to inflammation and tissue damage, which can cause a variety of symptoms, such as fever, rash, and swelling.

* By directly killing cells. Some viruses, such as rabies virus, directly kill infected cells. This can lead to tissue damage and a variety of symptoms, depending on the location of the infected tissue.

Viruses can infect people of all ages, but they are most commonly spread through contact with an infected person or animal. Some viruses can also be spread through the air, through contaminated food or water, or through contact with contaminated surfaces.