VOLSET FOUNDATION

                                     THE HIDDEN KILLERS

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 cannot 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.

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.

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 infected 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.

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 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.

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 outsides 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.

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.

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 cell's 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

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 cell's DNA. Instead, they pretend they are part of the cell's 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 cell's 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 cell's genetic code.

Retroviruses follow these steps:

1. RNA changes to DNA
2. DNA is incorporated into cell's DNA
3. DNA makes messenger RNA
4. Messenger RNA directs the rest of the cell to make viruses.

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.

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.

The good       

    Ref:      http://library.thinkquest.org/23054/gather/index.shtml