Viruses are very
simple forms of life, consisting of genetic information
- DNA or RNA - surrounded by a protective layer of
protein called a capsid. Some viruses have another
protective layer made of lipids (waxes or oils) called
an envelope surrounding them. Viruses are difficult to
identify, as they are too small to see under a light
microscope and are difficult to culture.
Viruses
are infectious agents that can be found in virtually all
life forms - humans, animals, plants, fungi, and
bacteria. When viruses infect a life form, referred to
as the host, they invade living cells, where the virus
replicates at an rapid rate.
Humans are in a
constant battle with viruses. Human vaccine is usually
reformulated each year to contain current antigenic
strains of viruses.
Human borne viruses can
spread in several ways from person-to-person. Depending
on the type of virus, catching it could be as simple as
breathing the same air as an infected person such as
with the common cold, or influenza, or by putting
something in the mouth that has been contaminated by a
person with, for example, Hepatitis A. Other viruses
include the Ebola virus, the West Nile Virus, and of
course HIV, the virus that causes AIDS. Viruses are now
thought to be implicated in up to one in five cancers.
Infected persons with no symptoms at all can still
spread a virus.
Viruses mutate all the time.
That's why we don't really have a cure for the common
cold, and why SARS, and the Avian flu, diseases of
animals are now a danger to human beings. HIV that
causes AIDS mutates so fast that the immune system
cannot keep up with this ever-mutating virus.
Plant viruses are transported by feeding insects or
plant pests, although some viruses are transmitted by
nematode worms or fungi, or transmitted by mechanical
means such as touching or rubbing leaves with hands or
tools contaminated by contact with diseased plants.
Plant viruses are responsible for major diseases and
yield losses of crops worldwide. Examples of plant
viruses are the Tomato spotted wilt virus, Cauliflower
mosaic virus, and the Tobacco mosaic virus which can be
harboured in cigarettes.
There is no cure for a
viral infection whether it be an animal, human or plant
virus. Viral infections cannot be treated with
antibiotics; in fact, in some cases the use of
antibiotics makes the infection worse. The vast majority
of human viral infections can be effectively fought by
the body's own immune system.
Information
obtained from the Wikipedia web site. Wikipedia the free
encyclopedia.
