It is hard to believe that a 'thing' so small and simple can cause so much havoc in the world.Viruses are so primitive that many scientists consider them to both living and non living things.In face they have the characteristics of both.
The Discovery of Viruses
As viruses are so microscopic they remained invisible until modern instruments were developed.But even before they were seen,some scientists though that they existed in the environment.The first such scientist was Louis Pasteur.In 1935 Wendall M.Stanley,an american Biochemist,was able to separate the virus from the plant cell in which it was growing. He.He was able to see the virus under an optical microscope,for the first time.Since the discovery of the electron microscope in the 1930's,virologists have understood several mysteriesabout the virus-its growth,structure and the changes it can cause in living things.
The Structure of the Virus
Viruses,unlike other organisms are not made of cells,Therefore,they lack some of the substances needed to live on their own.A typical virus has two basic parts,a core of the Nucleic Acid and an outer coat of protein.The nucleic acid contains the genes or 'instructions' which will determine how the organism will reproduce and develop.All other organisms larger than the virus have two types of nucleic acid,DNA and RNA.The virus has only one type of nucleic acid either DNA or RNA,never both.Hence,the virus is not a complete organism by itself.It enters another living cell and uses its material to live and reproduce.The protein coat of the virus gives it its shape.Some are like thin rods,others spherical,or tadpole like with tails attached.The protein coat also protein the nucleic acid and helps to get inside a cell.
How the Virus Reproduces.
Viruses that exist in the environment are carried into organism by air currents.Once inside,the virus will enter the cell and take control of it.The cell will then begin to produce the material needed by the virus to reproduce it self.Soon these new viruses will leave the cell and infect other cells.The new viruses become lifeless as soon as they leave the cell.But they return to life immediately on entering a new cell.They then begin the reproductive process.When a virus reproduces it changes the chemical make up of the cell.This change usually damages or kills the cell and causes disease if many cells are attacked.
The Virus and Disease.
Viruses can attack and cause disease in human beings,animals,plants and even bacteria.Viruses that infect people and animals may be breathed in or swallowed.They may even the body through cuts,insect bites and other means. Once inside,they can move around using their body fluids such as blood. Most viruses reproduce in specific cells for example,the viruses that cause colds reproduce in cells of the human respiratory tract.Besides the common cold other viral diseases in humans include, chicken pox, measles,mumps, rabies, polio,hepatitis,AIDS(Acquired Immune Deficiency Syndrome)etc.The AIDS causing virus is particularly dangerous because it stops the functioning of the body's immune system,the body's ability to fight diseases.Thus ,person with AIDS may get disease that a healthy person could fight off.
