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Over the countless number of years prevalent viruses have caused numerous infection and even fatality. Among these deadly viruses the one that stand out is the Polio Virus, which is short for Poliomyelitis. Even though Polio has been virtually eliminated in the western hemisphere, it is still endemic in under developed countries such as, Nigeria, Afghanistan, India, and Pakistan. Polio has been amongst the human race for decades and even centuries; however, it was not until the 1900's that Polio virus was considered to be endemic. Over time, Polio virus has become stronger and very successful in infection. In this paper, we will discuss how this vicious virus functions, the different ways to treat and prevent it, and how to make the world more polio free.
Polio, according to the dictionary, is an acute viral disease marked by inflammation of nerve cells of the brain stem and spinal cord. For the most part, when someone thinks of the word Polio the automatic assumption defines the word as a virus causing paralysis to its victims; however, that is not the only manifestation of the virus. In fact only about 1% of polio victims actually develop paralysis in the worst case scenarios. In reality polio is asymptomatic in 95% of the cases. There are three strands of Polio, PV1, PV2, and PV3. PV1 or abortive polio is the most common and virulent out of the three strands. Even though PV1 shows no symptoms in the infected, in some rare cases mild flu like symptoms may be seen. Since 1999, PV2 has not been observed in the world. Nonetheless PV2 is a more serious strand than PV1, and is associated with meningitis and is known as the non-paralytic polio. Finally, PV3 is the vigorous paralysis causing polio found in very rare occurrences; it is known as paralytic polio. Victims infected with PV1 and PV2 generally make a full recovery, however victims infected with PV3 will develop muscle paralysis that may even result in death. Nevertheless, infection of one strand does not result in immunity to infection of other stands. So if someone is diagnosed with abortive polio they are still susceptible to getting infected with either non-paralytic, paralytic polio or both.
An infection with polio usually occurs through the oral fecal route, such as intake of contaminated food, unwashed hands and fingers in the mouth, or ingestion of water contaminated with sewage material. The virus is commonly found in the throat and intestinal tract of an infected host. From the intestinal tract it can enter into the blood stream which allows it to travel to the central nervous system. There it can cause damage of the spinal cord cells. The death of these cells causes muscle paralysis, usually seen in the limbs. However, the virus is usually housed just in the intestinal tract for most of its life cycle.
Polio's life cycle is very comparative to most RNA viruses. Polio falls under the sub class of Enterovirus that is found amongst the class of viruses known as Picornavirus. These are RNA viruses classified as Baltimore class four. They are non-enveloped, single stranded positive sense RNA viruses with one large open reading frame. They are shaped icosahedraly with no 5' cap. However, their genome is slightly altered at both ends; at the 5' end a basic protein known as VPg (viral protein genome -linked) is covalently attached, which may act as a primer for RNA synthesis, and on the 3' end you will find a poly(A) tail (polyadenylation).
Polio, once it has infected the victim, starts its long journey by attaching itself onto the host's cells to start the production of more viruses. It attaches to the cell by the PVr receptor also known as poliovirus receptor. The virus will then enter the cell which can be done via two different methods. One technique it can use to enter the cell is through receptor- mediated endocytosis. This method involves absorption of molecules, in this case the virus, from outside of cell into the cell through engulfment. The second way it can enter is through a conformational change in the vesicles which will allow the capsid to form a pore where the RNA will be injected through into the host cell's cytoplasm. If the virus entered into the cell through endocytosis then it will undergo a step called uncoating. Uncoating will occur in a compartment that is formed inside the host cell. There it will uncoat the virus or break open the virus so the genetic material is easily available. Once the virus has been uncoded, then only the genome will be released into the cytoplasm.
Soon after viral genetic material has entered the cytoplasm, it is ready for transcription. Since Polio is a positive strand RNA virus, it can acts as an mRNA and does not need to be transcribed. It does not consist of the methylated cap at the 5', and as an alternative it has internal ribosome binding site (IRES) which allow the ribosomes to bind without the cap. The entire RNA is first, translated into a large polyprotein, and then soon after the proteases breaks the large protein allowing it to cleave itself into smaller proteins that will be divided into two proteins. Proteases will also shut of host cells protein synthesis to insure the host cells will translate the viral genome, and to promote cell death after the virus is assembled in order to spread the new virus.
Following translation and transcription the RNA will be replicated. Replication takes place exclusively in the cytoplasm. Due to the RNA strand, Polio will undergo replication twice. First, the original strand of RNA is replicated to make the complementary strand by RNA-dependent-RNA polymerase. VPg, mentioned earlier, is the protein that is found on the 5' end will acts as the primer for replication to be synthesized. Secondly, the complementary strand will be replicated as well. This is done make certain that the genome is replicated with the original base pairs and not the complementary base pairs.
Once the replicated strand and the translated protein are synthesized, the virus is ready to be assembled, packaged, and released with the new viral progeny. Like replication, assembly of the virus also takes place in the cytoplasm. The genome and sixty copies of each viral capsid proteins 1, 2, 3, and 4 are packaged inside the new mature capsids. Then the new capsids containing the viral information are released through a process called cell lysis, which involves bursting of the cell to release the viral capsids. Now the new progeny viruses are ready to infect other cells and start the process all over again.
As these small viruses start to replicate in the host's body, symptoms and signs are not publicized immediately. In fact it takes from seven to fourteen days for any symptoms to occur. Once contaminated with the disease, the victim is susceptible to transmit the disease a couple of day before and a few days after symptoms are present. Moreover, an infected person can continue transmitting the virus if it is still housed in the throat. If someone is infected with Polio, there are no true treatments for any of the polio strands.
Today, there are no medications for treating polio itself. There is only supportive treatment available for the symptoms of Polio. If infected with PV1 or PV2 fluids and medications such as ibuprofen are given to help ease the pain and fever. If infected with PV3 medications like antibiotics are given to prevent bacterial infection and breathing assistance may be required.
Back in the early 1900s, breathing assistance was provided through a spectacular machine known as the iron lung. An iron lung is about a 2 ton metal chamber that enfolds the patient's entire body except the head and with oscillating pressure helps the patient inhale and exhale. This machine was readily available to polio patients who suffered from chest paralysis. However, in the modern world, this enormous machine has been condensed down to a chest size. The new marvelous size allows the patient to be in the comfort of their home while receiving breathing assistance.
While there are no treatments for polio there are however ways to prevent it. There are two types of vaccines available for polio; one is an oral vaccine and the other is an inactivated vaccine. The inactivated vaccine (IPV) means that the virus is killed before being administered into the people. It was in 1952 when Dr. John Salk developed this vaccine. The oral vaccine (OPV) is the live small dosage of polio to the people. It was developed in 1958 by Dr. Albert Sabin. However, like a number of things in this world, both vaccines have their advantages and disadvantages.
The inactivated vaccine is considered to be easily managed since there is no risk of spreading the virus. Also this vaccine generates long term protection to all three strands of polio. On the other hand, the inactivated form of vaccination is awfully cost inefficient, it is five times more then the OPV and requires trained medical health works to administer it. There is no risk of VAPP (vaccine -associated paralytic polio) however, getting vaccinated by IPV makes the person act as a carrier of polio. The oral vaccine on the other hand, is considered to have biological and practical advantages. It is an attenuated vaccine which will develop and allocate lengthened exposure of immune system. This will result in more memory cell development. It also provides immunity to the virus however it prevents the vaccinated to be a carrier of polio. Also, OPV provides vaccination to surrounding people. Since it is a live vaccine, vaccinated people can transmit it to other unvaccinated individuals. However, unvaccinated individuals will be receiving the serotype of the lab vaccine virus and not the wild type. This will work as a vaccine for the unvaccinated and prevent the chances of getting the wild type polio. Nevertheless, the greatest advantage of all is that OPV is administered through sugar cube, or sugar liquid including the vaccine. This way any one can administer the vaccine. However there are still some disadvantages associated with the OPV. One of the biggest disadvantages is the VAPP. The OPV is live so therefore it can turn against the immunization once inside the body and cause a chronic infection instead of the normal acute infection. Nevertheless, both vaccines work hand in hand in immunizing the people against polio.
Today, the western hemisphere is pretty much polio free. This is because these vaccines and education have helped the westerns in advancing their step in the eradication of polio. Although polio is not easily identified, vaccines are available throughout the world. More and more people are standing up, especially in countries such as India and Pakistan, to help educate people and provide vaccinations. Despite the few glitches in the vaccines, they overall work splendidly and herd immunity is the best way to go. If we slowly keep spreading and continue to urge the people to get vaccinated we can be closer to the eradicated of polio.
Over all, this non-enveloped, single stranded positive sense RNA endemic virus is not as vicious if caught in time. However, this asymptomatic virus can become problematic in rare cases. Although replication and transmission of polio is well thought out, this overly developed virus is slowly diapering from the world due to advancement in research and understanding of the virus. As our technologies advance we can surely promote to a better lifestyle without Polio. This deadly disease has been haunting the human race for decades. If we keep using preventive strategies, vaccinations, and education we can win the fight against polio. Finally after intensive research being preformed, and comprehension of how polio works, science has given us great new hope of a polio free world that may rest before us.