Patrick Bardill, Ph.D.:
Viruses are infectious agents that can only replicate inside a living host cell. They consist of genetic material wrapped in protein and sometimes lipid membranes. This genetic material can be RNA or DNA, depending on the type of virus. A virus enters a host cell and uses the machinery in that cell to create more copies of itself. New viruses leave the host cell by either pushing through the host membrane, which leaves the new virus with a lipid membrane, or when the host cell dies and ruptures.
Viruses can cause symptoms through stimulation of the immune system or damaging tissues in your body. It is usually a combination of these processes that produce disease pathology and symptoms.
For example, fever is a reaction from your body that raises your internal temperature to fight an infectious agent. However, in some individuals, the immune response can get out of control and be harmful to the person.
Jack Lipton, Ph.D.:
First thing to know is that viruses are not fully alive. A virus needs a living cell in order to reproduce and complete its function, which is to make more viruses.
When I was in high school, viruses were explained to me like this:
A virus is like a robot on a motorcycle.
The robot goes into a factory — a cell — and it takes it over. It changes around the machinery so that factory only produces robots and motorcycles. Then, after it uses up all the materials in the factory, it releases all of the robots on all of the motorcycles that the factory made, and they go to other factories to do the same thing all over again.
When we think of the illnesses that are produced by viruses, most of the symptoms you would associate with the illness come from your body’s immune response to this foreign invader. When your body finds a foreign invader – bacterium, virus – it uses the immune system to clean things up.
To do that, it uses chemicals that signal immune cells to move to the area. The process of releasing clean-up substances, which are toxic to the bacterium or virus, produces inflammation as a by-product. A fever is your body changing its thermostat setting to create an inhospitable place for invaders to live, but that process makes you feel sick. So your own immune system in its battle against invaders makes you feel sick. We call the by-products of these battle tactics symptoms.
The severity of someone’s illness from something like the flu or a coronavirus is often related to the magnitude of their immune response to the invader. If you have a very active immune system, you’ll produce a huge response to the infectious agent, and in the process of doing that, you’ll have worse symptoms.