WHAT IS A VIRUS

WHAT IS A VIRUS ???

A virus is an infectious agent that is the simplest form of life, if life is defined as having the capacity to reproduce. Viruses indeed have that capacity but only when they are in a host cell, when they capture the replicating mechanism of the cell to duplicate the virus in many copies. These new viruses then may invade more cells and repeat the process, which explains how rapidly an infectious disease may progress.

Many people scoff at the idea of calling viruses “living” because they are so simple, composed of nucleic acid (DNA or RNA) and an outer structure that “holds” the contents together..a protein coat known as a capsid.

As far as I am concerned even though they may be obligate parasites (as are some bacteria), their basic structure and ability to replicate is why I refer to them as living. But that is a not very important difference even though some people take the argument seriously. What does matter is that they are capable of invading cells and taking over, sometimes causing serious disease, sometimes causing death; they may be transmitted as airborne particles or by ingestion as are most pathogenic bacteria. They are increasingly responsible for some of the most serious diseases emerging around the world, and are considered the most probable cause of the next pandemic, which could sicken and kill a large proportion of humanity.

Human activity is the major reason for “emerging viral diseases” because of a process called “spillover”. This refers to a disease caused by a pathogen which lives within a host animal without causing a disease in that host, but which, when infecting another animal (like humans) may cause severe disease. That is the story of how AIDS became a worldwide disease.

The transmission from reservoirs to susceptible hosts is frequently caused by changes in the ecosystem of the reservoir, which may cause those animals to leave that ecosystem and invade new areas, or which may involve humans invading their ecosystems, as when they destroy forests to crease farmland. In those cases the humans come into contact with the reservoirs by various routes, such as killing and eating them for food.