#1. What is a Virus

While diseases caused by viruses date back to ancient history, the causative agent, a virus, remained  mystery until the middle 1900s. Viruses are too tiny to be observed under a light microscope; they will pass through most filters and they cannot be propagated on any medium or nutrient broth. Hence viruses were not seen and identified until the mid 1900s. It required development of the electron microscope and modern chemical technology.

It turned out, a virus is simply a bit of DNA (or RNA) surrounded by a protective coat of protein. (See: https://www.utmb.edu/virusimages/the-virus-images) There is no chemistry (enzymes or pathways) for growing, replication, making proteins or anything else. Hence, viruses cannot rightly be called living organisms; they are better called “infectious particles”. 

How does a virus cause disease if it is not, itself, a living organism? On gaining access to a living cell, the virus is able to hijack the cell’s metabolic machinery; has the cell read the virus’s DNA, which directs the cell to drop whatever it is doing and start making more virus particles. When the cell is full of virus particles, it ruptures releasing the many hundreds of new viruses, each capable of repeating the process. Is it any wonder that a virus disease can be fatal?

The body has a defense mechanism, the immune system. Via this complex system, the body is able to recognize invading foreign (virus) particles. In turn, it produce antibodies, special cells that are able to attach to and destroy the virus particles. This takes time, however. Thus, it is a race between the virus invasion and the response of the immune system. The outcome of the race is the difference between recovery and death. 

There are no medicines (yet) that effectively prevent or stop a virus from doing its thing. The best remedy is prior vaccination. Vaccination amounts to injection or otherwise exposing the body to some facsimile of the virus particle. This is recognized by the immune system as the actual virus and it makes antibodies accordingly. With antibodies on hand, the body has a significant head start in the race between the virus and the immune system. In most cases, the virus is destroyed before it gets a start. Who would not want such protection against such deadly infections. 

There is obviously a great deal of research involved in developing, testing, and producing a vaccine for a given disease, Then new diseases keep coming along, e.g. Covid 19, and old disease viruses mutate to new forms. Therefore, this is an ongoing process always with new challenges. It is the section of biology called virology. A scientist in the field is known as a virologist. Consider becoming a virologist.