How a virus works

How a virus works

Author: John Lui
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How does a virus infect?

How do viruses infect?

Viruses do not have the chemical machinery needed to survive on their own. They, thus seek out host cells in which they can multiply. These viruses enter the body from the environment or other individuals from soil to water to air via nose, mouth, or any breaks in the skin and seek a cell to infect.

A cold or flu virus for example will target cells that line the respiratory (i.e. the lungs) or digestive (i.e. the stomach) tracts. The HIV (human immunodeficiency virus) that causes AIDS attacks the T-cells (a type of white blood cell that fights infection and disease) of the immune system.


Viruses are not simply taken into cells. They must first attach to a receptor on the cell surface. Each virus has its specific receptor, usually a vital component of the cell surface. It is the distribution of these receptor molecules on host cells that determines the cell-preference of viruses. For example, the cold and flu virus prefers the mucus lining cells of the lungs and the airways.

Life cycle of a basic virus

There are a few basic steps that all infecting viruses follow and these are called the lytic cycle. These include:
A virus particle attaches to a host cell. This is called the process of adsorption
The particle injects its DNA or RNA into the host cell called entry.
The invading DNA or RNA takes over the cell and recruits the host’s enzymes
The cellular enzymes start making new virus particles called replication
The particles of the virus created by the cell come together to form new viruses. This is called assembly
The newly formed viruses kill the cell so that they may break free and search for a new host cell. This is called release.

Source: Dr Ananya Mandal, MD

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