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
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.
A 3-dimensional representation of the Canine Adenovirus Virus
www.grandarts.com/
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.
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.
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
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.
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.
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.