----- Original Message -----
From: "HepC Info" <hepcvets@...>
To: "brad scalf" <bscalf@...>
Sent: Tuesday, August 27, 2002 4:57 PM
Subject: HEP C INFO: The Basics Of A Virus:Characteristics Of A Virus


> The Basics Of A Virus:
>
> Characteristics Of A Virus
>
> Viruses are different from anything else found on earth and are mainly
characterized by their size, shape, and half alive/half dead existence.
>
> The big difference between viruses and all else, is that fact that viruses
are so small they can not be viewed without the help of an electron
microscope . This is because viruses are, on average, smaller than a regular
wavelength of visible light. In effect, the viruses can hide between light
waves, thus making them colorless. They can not be seen by the naked eye or
a regular microscope. Viruses are so small in fact, that the largest virus
is equal in size to the smallest bacteria. The smallest virus measures only
20 nanometers in length. Because of their incredibly small size, viruses are
extremely hard to study and understand.
>
> Shape is also a defining characteristic of viruses. The basic shapes
viruses tend to take are rods, filaments, crystals, helixes, polyhedrons and
spheres, with added extensions. Almost all human viruses are close to being
spherical. Every virus carry proteins and nucleic acids in a protective
coat. This protective membrane is called the capsid. Extensions on any virus
are called antigens. The antigens allow viruses to identify, attack, and
enter its target host. Viruses are not classifiably alive or dead. They seem
to be in limbo between each state. Viruses exist this way because they are
strictly parasites. That is, they can not survive and thrive without a host
or group of host cells. The hosts provide viruses with all the chemicals and
molecules they need to survive and reproduce. You might think of viruses' as
robots that need to take over a factory to make more of themselves. Without
that, the viruses are dormant . Viruses can lie dormant within any host or
environment until the proper conditions for their activity are provided.
This is why we sometimes say that viruses have incubation periods of certain
lengths. Some viruses are also classified as 'persistent viruses'. Such
viruses can enter and exit host cells without killing them. Even so, each
different virus is stimulated by different conditions and they all have
different, specific functions they affect in their host. They are mysterious
and dangerous creatures.
>
> Evolutionary History
>
> Scientists say, that viruses have existed since the beginning of life on
Earth. Viruses have plagued animals, plants, fungi and protozoa as long as
anyone can possibly trace back in time. Even as the years passed, and life
evolved from a primitive 'primordial ooze' into more complex vertebrates,
viruses maintained their reign of terror. But does this mean that viruses
haven't changed at all over the millennia? Of course not. Just as life
evolved, developed and adapted to the new and changing environment, so did
viruses.
>
> In their humble beginnings, viruses existed primarily as unprotected
genetic strands that carried hereditary information from newly developed
life to its offspring. They were messengers. Over time the ever-changing
environment of Earth influenced many changes in the method of this transfer
of information. The genetic messengers evolved as their hosts did, and they
eventually developed protective outer casings to protect themselves from the
elements. As life became more complex and cells began to self-reproduce,
viruses lost their primary function. Cells took over the messenger role, and
so viruses began to infect rather than exchange genes with their hosts.
Almost seemingly set on revenge, the newly evolved viruses infected every
living thing, and proscribed each cell with their own genetic formulas. They
became parasites. They were unstoppable.
>
> Continuing to progress, viruses developed the ability to jump from species
to species by changing their genetic material to fit the new hosts' bodies.
They were determined to survive throughout the centuries no matter the cost
of life. The viruses of today are highly complex and elusive. Over their one
million plus years on Earth, viruses have developed their own protection,
means of survival and efficient ways of infecting their hosts. The medical
researchers of today are constantly studying viruses in hopes that we will
soon be able to understand them. But fighting viruses is like fighting an
enemy who keeps up with every new advancement in weapons technology; the
more time they have, the more precocious and powerful they become.
>
> Vaccines
>
> About 200 years ago Edward Jenner might as well have been known as the
luckiest man alive. It was in the year 1796 that this country doctor made
one of the most astounding discoveries ever. Of course, at the time Jenner
didn't know the magnitude of the medical powers he was experimenting with.
The experiment Jenner performed would now be considered extremely crude and
dangerous. While practicing medicine in the small town of Gloucestershire,
England, he decided to experiment with the effects of cowpox and smallpox.
Cowpox was a common occupational hazard in the dairy country of England.
Coming from sores on the udders of dairy cows, cowpox was a highly
contagious disease with caused fever, nauseas and pustular sores on certain
areas of the skin. Based only on an old wives' tale he heard as a teenage
apprentice -- milkmaids who had been infected with cowpox never became
infected with smallpox--Jenner decided to infect his first son with cowpox.
A few days later, he infected Ed Jr. with smallpox. His son never got the
disease.
>
> With this encouraging result, Jenner decided to infect a young boy, James
Phipps, with the contagious material of both diseases. This boy's cowpox
infection also healed quickly, and he was back in perfect health after only
a short amount of time. Afterwards James was injected with smallpox, but was
seemingly unaffected, just like Jenner's son. Although no one at the time
understood what exactly had prevented the boy from becoming infected with
smallpox, it was certain that this obscure doctor had performed a miracle.
Dr. Edward Jenner had discovered the first official vaccine, recorded on the
14th of May 1796. Throughout 1796, cowpox invaded the English countryside,
providing Jenner with yet another opportunity to test his promising
vaccination theories. He not only began investigating cases of milkers who
were protected from smallpox by cowpox, but he also studied other
inoculations for diseases such as swinepox and a number of bacterial
infections. Jenner went on to publish papers on his experimentation. The
paper describing the first discovered vaccination was appropriately titled,
"An inquiry into the Causes and Effects of the Variolae Vaccineae, a Disease
Discovered in some of the Western Counties of England, particularly
Gloucestershire, and known by the name of the Cowpox by Edward Jenner, M.D.
F.R.S. & C." Within two years, it was translated into many languages and
reprinted all around world. Jenner became famous, but met both good and bad
criticism. Newspapers and Magazines mocked his work. They would print
cartoons showing vaccinated patients sprouting horns and mooing, with titles
like "The Cowpock ? or the Wonderful Effects of the New inoculation." Jenner
had no idea why the vaccination worked, just that it did, but he spawned the
first organized field of viral study. A year before he died in 1823, another
great man that would change our view of the world was born.
>
> Discover Of The Virus
>
> Ninety years after Jenner's first vaccine experiments, a French chemist
and renowned microbe hunter, Luis Pasteur, performed a similar marvel.
Pasteur, at the time, had been studying the effects of another deadly
disease of that time: rabies. He had done a great deal of research with
animals, and had begun to notice certain things about infected body tissue.
It seemed that as the tissue was transferred from species to species, it
became less infective and less potent. Pasteur's theory, was that if this
weakened tissue was somehow injected into humans already infected by rabies,
that it would protect them from the disease's deadly effects. Pasteur, like
Jenner, first tested his vaccination on a young boy, this one bitten badly
by a rabid dog. This vaccination was also successful, and the boy remained
rabies free for the rest of his life. Pasteur was more conscious of what he
was doing than did Dr. Jenner, but he was never able to locate the
'bacteria' that he thought caused rabies.
>
> Still, even with these amazing break-throughs in disease prevention, none
of the scientist of the time had any clue to what kind of 'monster' they
were dealing with. In 1892, Russian Dmitri Ivanovski discovered the very
first clue that set these microbes in a class of there own. Even though he
was not in the practice of studying human diseases, Ivanovski gave us the
first proof that viruses so exist. Ivanovski's main research included the
tobacco mosaic disease. Using special filters Ivanovski attempted to
separate out the bacteria that was causing the infection. To his dismay,
even after several iterations of the filtering process and exposing it to
alcohol and fermalin, the tobacco plants continued to become infected and
die.
>
> Six years later, a Dutch botanist, Martinus Biejerinck performed a similar
experiment. However, he had not read about Ivanovski's work since it was
only published in not very well known Russian journals. He performed the
same filtering method, but he took it a step further. Though the filtering
method might have removed the bacteria, it might not have removed toxins
created by bacteria. These toxins could also cause diseases. To see if it
was the toxins, he infected a healthy plant and then tried to infect another
plant with fluid from the now infected healthy plant. If it was toxins, the
next plant would not be infected. It did however, telling Biejerinck that it
wasn't toxins. Trying something different, he let the sap from an infected
plant sit for three months and tried to infect a healthy plant. It still
infected. He tried adding alcohol and formalin which would be enough to kill
microorganisms. It did nothing to prevent the fluid from infecting again. So
what was causing this disease in these plants if it wasn't toxins or
bacteria? Perhaps it was bacterial spores? They could pass through the
filters. To test this, Biejerinck heated the fluid to ninety degrees
centigrade. All of a sudden, the fluid stopped infecting the plants!
However, this didn't prove it was bacterial spores. Quite the contrary. It
takes a hundred degrees centigrade to kill the spores, not ninety. This was
something else completely.
>
> Through their research, Biejernick and Ivanovski had discovered a new
disease-causing agent. Biejernick believed this agent to be a fluid, he
called it a "contagious living fluid." Later this liquid was renamed 'virus'
for the Latin word poison.
>
> The Host
>
> The average virus experiences a rather dull presence on Earth. In fact,
the sole purpose of a virus's existence is to duplicate itself and create
more viruses.
>
> There are basically three completely different 'types' of viruses. They
are animal, plant and bacterial viruses. Each type of viruses is independent
of the others. Meaning that a plant virus can not be transmitted to a
bacterium and such. So far, there has never been any type of life found on
Earth, which is not susceptible to viruses. Some species have more than one
hundred different viruses plaguing their kind.
>
> Within each classification, viruses are specific to a certain kind of
cell. Viruses tend to be very picky about their hosts. They also have
preferred ways of entrance into their hosts. A virus' method of entry is
very specialized, and it is one of the main ways a virus is able to locate
it's victims. Take, for example, a virus that targets host cells located in
the stomach. If a person inhaled such virus particles they would not be
harmed. On the other hand, if any virus molecules were ingested into the
stomach, the hosts would immediately be infected. Some viruses even require
cells to be in certain stages of life. These viruses may prefer actively
dividing cells or cells that are younger.
>
> Viruses use a simple marking process to identify the cells they attack.
All viruses have special molecules on the outer covering that can search out
and identify particles on cell surfaces. Every cell has a unique set of
markers that identifies it to other cells. These surface molecules dictate
the cells the each virus can recognize and infect. The interaction between
the virus surface and the cell surface determines whether infection of the
host will be successful or not. Host cells have to be of a very specific
type or viruses will not be able to replicate and survive. All cells have
surface receptors, which viruses use to identify the cell by their markers
and if they match, attach themselves to it. Both sides have to be in good
contact, and conditions have to be just right. When a virus securely
attaches itself to a host cell in good condition, the infection begins.
>
> How Viruses Infect
>
> Viruses do not possess any life sustaining characteristics, and do not
require any nutrients. In fact, without a proper host viruses lie dormant
indefinitely. Infection takes place when a virus comes in contact with its
intended host. As soon as a virus encounters its victim, it attaches itself
to the organism. Furthermore, most viruses prefer a certain type of host
cell and a specific mode of entrance. Naked viruses, those without a
structured casing, directly enter the cells while other types of viruses
fuse themselves to the outside of their victims and inject their genetic
material inside the cell. Once the genetic material of a virus is
transferred to the host cell, the virus can 'take over' by incorporating its
DNA into the hosts DNA much like they used to do in the prehistoric days.
The infected cell is essentially a factory in charge of virus manufacturing.
In a process called budding, mature viruses leave the cell a few at a time.
Lysis is the much more devastating cousin of budding. In lysis, the cell
membrane of the host is completely destroyed, killing the cell. The new
viruses are unleashed instantaneously. Almost all viral infections result in
the death of the host, but in rare cases viruses leave their host cells
alive. When this happens the cells are normally damaged beyond repair. With
each successive transmission between hosts a virus is able to replicate
itself thousands of times, and ensure the continuance of its reign of
terror.
>
> Types Of Infections
>
> Most people relate viruses with 'the cold' and 'the flu,' viral infections
that bring out a familiar set of symptoms, and then leave as quickly as they
show up. These are examples of acute infections. Acute infections cause many
of the minor illnesses that humans have experience with. This type of viral
infection is, on the most part, rather harmless causing discomfort and minor
indications of cell damage. Acute infections, however, can become much worse
if they are recurring and do less damage to host cells. In this case acute
infections become chronic infections. Chronic infections can be dangerous
and sometimes deadly. In cases of chronic infection host cells may not be
damaged at all, but their functions may be disturbed. This can cause serious
recurring illness and disease. In many cases, chronic infections can be
monitored and the viruses that cause them can be cultured in labs. However,
scientists can not culture the types of viruses that cause latent
infections. Latent infections come from viruses that can manage to evade
attacks of the host's immune system. Latent viruses are persistent and
frequently cause deadly diseases.
>
> What's An Infection?
>
> In normal cells, nucleic acids make up the all the genetic material found
in the nuclei. Bundles of nucleic acids are collectively called genes, and
they stick together to form chromosomes. There are a total of 46 chromosomes
in every normal human cell nucleus. The smaller packets of nucleic acids
make it possible for normal cells to manufacture proteins, enzymes, energy
and heat. They also allow cells to carry out the everyday functions of life
and pass on their characteristics to their offspring. If we take the time to
inspect these nucleic acids more closely, we would see that they are
specialized molecules known as DNA (deoxyribonucleic acid) and RNA
(ribonucleic acid). These molecules are the basic building blocks of all
life and act as the master plans for all the cells in a body.
>
> While DNA can be considered the director of operations, RNA specializes in
carrying 'messages' from the nucleus to different parts of the cell. DNA is
made up of many separate fragments that each contains different coded
messages. In a process called transcription, a rough copy of the DNA's gene
is decoded and written onto a strand of RNA. The result is a form of
messenger RNA, which travels to each part of the cell carrying specific
instructions and commands. This process is vital for the survival of cells
in a body, and if something hampers its completion or alters the
instructions, the results can be deadly.
>
> Viruses are tiny packages of genetic material without a living cell
enveloping them. The key to their power is the nucleic acid they possess.
When a virus attacks and infects a vulnerable living cell, it pours its own
DNA and/or RNA inside. Once inside, the hereditary material begins a virtual
Coup d'état. It attaches itself to the cells existing DNA and sets up a new
command system. Now, instead of producing substances the cell needs to
survive, it is forced to produce viral nucleic acid. One cell can be used to
create thousands of new, mature viruses. The fastest virus only needs 24
minutes to explode a cell and release new virus particles. Cells are damaged
and destroyed with each new birth, and chaos is all that is left in the
wake.
>
> RNA/Retroviruses
>
> The majority of viruses force hosts to do their bidding by regular DNA to
RNA transcription. There are, however, other types of viruses called RNA
viruses that follow a slightly different method. RNA viruses such as polio,
are made up of messenger RNA instead of the regular DNA. They skip the step
of incorporating their genetic material into the cells DNA. Instead, they
pretend they are part of the cells regular messenger RNA and directly pass
messages to other parts of the cell to start making viruses.
>
> Usually, viruses follow this method:
>
> * 1. Incorporate DNA into cells DNA
>
> * 2. DNA makes messenger RNA
>
> * 3. Messenger RNA directs the rest of the cell to make viruses.
>
> However, RNA viruses skips some steps:
>
> * 1. Messenger RNA directs the rest of the cell to make viruses.
>
> Another type of RNA viruses called retroviruses are only able to take
control of these cells in reverse. Retroviruses contain a shorthand code of
directions coded on RNA strands. For these viruses to be able to replicate
and produce protein, they have to convert RNA messages to DNA. Retroviruses
contain a special enzyme called reverse transciptase, which allows this
process to take place. Once the coded messages are translated into DNA, the
virus' message is incorporated directly into the cells genetic code.
>
> Retroviruses follow these steps:
>
> * 1. RNA changes to DNA
>
> * 2. DNA is incorporated into cells DNA
>
> * 3. DNA makes messenger RNA
>
> * 4. Messenger RNA directs the rest of the cell to make viruses.
>
> HIV, the virus that causes AIDS, is one of the better known retroviruses.
Some scientists theorize that RNA viruses are the cause of cancer. Although
it is not yet proven, this solution would explain how the form and function
of cancerous cells are affected.
>
> Beyond Viruses: Viroids
>
> For the longest time, virologists were fairly certain that there was
nothing on Earth comparable to viruses. Then, in 1964, Dr. Theodore Diener
made an amazing discovery, which questioned these old theories. Diener had
accidentally stumbled upon a new and exotic infecting agent. This new
microorganism had the same devastating effects as viruses, but lacked many
of the properties that define viruses. Viroids are found only in plants and
are believed to be a more primitive version of the ordinary virus. In fact,
viroids may be living fossils of the genetic messengers (see The
Evolutionary History of Viruses) which existed before animal cells were
created. Viroids are naked strings of amino acids with absolutely no
covering of their genetic material. They are free-floating, single stranded
RNA. Viroids are known for their simplicity. Once thought to be the smallest
infectious agents, Viruses are now considered larger and more complex than
viroids. There was great skepticism concerning his discovery, but Diener was
eventually able to prove the existence of the viroid, the lethal younger
brother of the virus.
>
> Virus Research
>
> Everyday, virologists study harmful viruses trying to understand exactly
what these mysterious beings are, and how they behave. The goal of their
research is simple. They want to find ways to prevent control and ultimately
cure many of the deadly viruses that plague life on Earth. Already their
work has been able to prevent several epidemics and wipe out the threats of
many viruses. In fact, many vaccines can already control viruses such as
smallpox, yellow fever, polio and influenza. The most dangerous viruses,
including AIDS and certain brain-destroying viruses are of the highest
priority right now. An incredible amount of time and money is being poured
into the search for medications and vaccines to help solve their devastating
effects. A drug called AZT is one important result of these studies. AZT
blocks virus replication in cells and has helped many AIDS patients to
resist infections. Further studies are also being done to try and connect
viruses with cancer.
>
> By studying viruses directly, scientists have been able to learn a lot
about ourselves in the process. We have discovered an incredible amount of
information about the actual DNA, RNA and genes of living beings. Once they
are able to identify the life controlling functions of specific genes, they
may be able to design special drugs to target virus vulnerabilities.
>
> Unfortunately, development of drugs cost biotech companies millions of
dollars of research and testing. This limits the types of disease that are
being studied. Diseases that predominately affect the poor are often ignored
because they are not "profitable" to look at. However, diseases that affect
the poor are the ones that are of the greatest concern. These are the
diseases that affect the majority of the human population. Thus, the irony
of the whole situation.
>
> We've come a long way since Jenner and Pasteur. With our new technology
and methods of experimentation, scientists aim to ultimately strip viruses
of their mystery, and learn how to prevent the disaster they cause.
>
> General Prevention Of Viral Infections
>
> There are no miracle drugs against viruses. However, there are a few
antivirals that have been developed, but they don't come close to being as
effective against viruses as antibiotics are against bacteria. Vaccines are
currently the best medical option available in preventing and treating viral
infection. We are still far away from finding effective medical treatments
against these diseases.
>
> The good news is that most of the effective preventive measures aren't
related with medicine at all. For example, the best way to prevent blood
related viruses such as HIV is to:
>
> * 1. Practice safe sex.
>
> * 2. Don't be involved in sharing needles.
>
> * 3. Avoid having contact with an infected person's blood without proper
protective measures.
>
> Plus, the biggest advancement we have against fighting any disease, not
just viral ones, comes from the invention of the... toilet! Yup! Sanitation
is the best method we have of protecting humans. Most of these diseases
plague poor third world countries where sanitation is not very good. While
most of the U.S. are relatively sanitary, with our sewer systems, clean
water, etc., parts of this country as well as other industrialized nations
are also faced with similar sanitation problems. As long as these places
exist, viruses and other diseases will continue to be a problem for the
human race. These Hidden Killers will continue to stalk.
>
> Source:http://hepcvets.com/viral/basics.html
>
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