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What Is A Virus?




What is a Virus?

What is a Virus?


How do Viruses Work?

How are Viruses Classified?

Can Viruses Change?

How do Animals Defend Themselves?

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Glossary


  What is a Virus?

A virus is a very tiny infectious agent.  Viruses are so small that the information the virus can carry is actually not enough to allow it to make copies of itself on its own.  Therefore, a virus must enter, or infect, a living cell and highjack that cell’s machinery to be able to multiply. After the new virus copies have been synthesized and assembled they are able to leave the living cell and infect others.  

adenovirus 
A 3-dimensional representation of the Canine Adenovirus Virus
www.grandarts.com/art/adenovirus-2244.jpg

Structurally viruses are quite simple and are mainly made up a small amount of genetic information surrounded by a protein coat called a capsid.  A membrane referred to as a viral envalope surrounds some viruses.  The genetic information carried by viruses can be in the form of RNA or DNA.


   
How do Viruses Work?

Viruses lead very simple lives, if you consider them to be alive that is!  All they do is exist and make more viruses. A virus enters a cell by first attaching to a specific structure on the cell's surface. The result of viral infection is the exposure of virus genetic material inside the entered cell. Then, the virus material essentially takes over the cell and nothing but viral parts are made, which assemble into many complete viruses. These viruses are mature and leave the cell either by a process called budding, in which case one or a few viruses leave the cell at a time, or by a process called lysis, in which the cellular membrane ruptures and releases all of the virus particles at once.

Viruses do not only infect people and animals.  So far, there is not a living thing identified that doesn't have some sort of susceptibility to a particular virus. Plants, animals, bacteria - every living thing, whether multicellular or single-celled, can be infected with a virus specific for the organism. And, there may be 100 or more different viruses which can infect that species alone. So, whenever viruses are discussed, they are discussed as being either plant, animal or bacterial viruses.


   
How are Viruses Classified? 

Viruses come in all shapes and sizes and have a huge variety of different kinds of organization of basic genetic material within them. It is the arrangement and type of genetic material which is the method used for classification of a given group of viruses. For example, the animal virus group can be divided into the following groups: DNA viruses, which are subdivided into double-stranded DNA and single-stranded DNA;  and RNA viruses, which are subdivided into double-stranded RNA; single-stranded RNA, and, retroviruses. However, for all viruses, regardless of the kind or arrangement of genetic material, the virus is capable of replicating within a living cell and can produce offspring which are usually absolutely identical to the original virus

   
Can Viruses Change? 

Sometimes during the process of viral replication, mutations do occur. If the mutation is harmful, the new virus particle might no longer be infectious. However, because a given virus can generate many, many copies of itself, even if 200,000 particles are no good, 100 might still be just fine. Also, some mutations don't lead to harm to the virus, but instead lead to a functional but now brand-new strain of virus which has never been seen by the immune system of the host organism.


   
How do Animals Defend Themselves?

Luckily, animals have several methods of protecting themselves from viral infections. First, if a particular virus infects one or more cells of a given tissue in our body, the infection leads to the synthesis and secretion of substances called interferons. Interferons are proteins that interact with adjacent cells and help these cells become more resistant to infection by the virus. Following interferon release, the body's immune system takes over and begins to fight the infection by killing the virus on the outside of the cells, and killing the infected cells too. Usually with time the virus will be completely removed, and the animal will get over the illness.

Recently, there have been anti viral drugs designed in the laboratory and isolated from natural sources that are being used to fight certain viral infections.  However, these drugs are generally expensive and are often dangerous to take.  The best option for control and prevention of viral disease today is vaccination.