Viruses are tiny infectious agents that need a host cell to reproduce. They don't have the cellular machinery to replicate independently. Instead, they invade cells and hijack their cellular mechanisms to create more viruses.
The Viral Replication Cycle
The process generally involves these steps:
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Entry: A virus enters the body through various routes, such as the nose, mouth, eyes, or skin (Source: How a Virus Infects the Body). Once inside, it travels along cell surfaces until its proteins bind to specific receptors on the host cell (Source: How viruses travel through the body. Once a virus gets into a host's body, it travels along the surfaces of cells until its proteins begin to bind with receptors on the cells). This binding triggers fusion, allowing the virus's genetic material (DNA or RNA) to enter the cell (Source: How viruses travel through the body. Once a virus gets into a host's body, it travels along the surfaces of cells until its proteins begin to bind with receptors on the cells).
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Hijacking: Inside the host cell, the virus releases its genetic material and proteins (Source: After entering a host cell, a virus hijacks the cell by releasing its own genetic material and proteins into the host. It uses the host's cellular machinery to...). It then takes over the cell's machinery to create copies of its own genetic material and proteins (Source: The virus uses the host cell's machinery to make more copies of itself. Pieces of the virus assemble, wrapping up the genetic material in the...). A virus puts its genetic information into the cell, providing instructions for the cell to create more viruses (Source: A virus puts its information into a cell—a bacterial cell, a human cell, or animal cell, for example. It contains instructions that tell a cell...). Some viruses, like retroviruses, even integrate their genetic material into the host cell's chromosomes (Source: Some types of virus, such as retroviruses, integrate their genetic material (including the new gene) into a chromosome in the human cell).
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Assembly & Release: New viral components assemble, forming complete viruses. These new viruses are then released from the host cell, often destroying the cell in the process, to infect other cells and repeat the cycle (Source: The virus uses the host cell's machinery to make more copies of itself. Pieces of the virus assemble, wrapping up the genetic material in the...).
Types of Viruses & Their Mechanisms
Viruses vary widely in their structure, genetic material (DNA or RNA), and method of infection. For example, mRNA vaccines work by introducing a piece of mRNA corresponding to a viral protein, triggering an immune response without causing infection (Source: mRNA vaccines work by introducing a piece of mRNA that corresponds to a viral protein, usually a small piece of a protein found on the virus's outer membrane).
This explains how viruses generally work; however, specific mechanisms vary significantly depending on the virus.
