Poliomyelitis, otherwise called polio, is known to be a highly infectious disease caused by a virus through invasion of the nervous system thereby causing paralysis in some body parts especially the limbs within hours (http://www. polioeradication. org/disease. asp). Poliomyelitis can generally be defined as the process that involves the inflammation of the gray matter of the, leading to the destruction of the multipolar cells. Although it is generally regarded to attack indiscriminately with regards to age, over 50% of total cases reported are children under the age of five years (http://www.
polioeradication. org/disease. asp). Polio is in the family Picornaviridae and subfamily Enterovirus. It is caused by a virus called poliovirus, which are naturally host specific to only human being. They are usually ingested by the victim through the mouth, before they move along the alimentary canal and settle in the gastrointestinal tract. The taxonomy of the poliovirus is as indicated in the table below; During the time of movement, it multiplies through the throat up to the gastrointestinal tract before joining into the bloodstream from where it is transported to the.
Here, it replicates to overwhelming numbers before starting the process of destroying the cells of the motor neuron (http://american history. si. edu/polio/virusvaccine/how. htm). This makes them very dangerous since it these motor neurons that control the muscles responsible for respiration, swallowing, circulation, and legs, trunk, and arms. Reasons for the preference of these motor neurons still remain a mystery (http://americanhistory. si. edu/polio/virusvaccine /how. htm). Poliovirus was isolated as early as 1909 by researchers Erwin Popper and Karl Landsteiner.
It was described as a small Enterovirus that it consist of a positive sense Ribonucleic Acid (RNA) genome, which is about 7. 5 kb long and is enclosed within a protein shell known as a capsid. It is this protein shell that helps not only to protect the genetic material of the virus, but also aids it during the process of attacking the host cells. The genome is only able to encode the number of genes small enough to encode the viral proteins that is just enough for the effective invasion by the virus as well as replication within the human cells. This number could be as many as 10 genes (Rogers, 2007).
There are three main types of poliovirus, each with different capsid proteins as well as numerous strains. These types include Type 1 (PV1), Type 2 (PV2) and Type 3 (PV3). All these are very virulent, though the PV1 is the most virulent and since it is the most common, it is closely associated with paralysis. All these types of poliovirus exhibit similar symptoms of the poliomyelitis disease (http://www. medscape. com/viewarticle/416890). During the attack, the poliovirus gets attached to the protruding structure of protein found on the surface of the nerve cells, whose function as well is not very clear, and begins the infections.
The virus does gain entry by binding itself to the poliovirus receptor (CD155), which is found at the surface of the cell. The engagement between the poliovirus and the CD155 causes conformational change of the virus necessary for its entry. This change is mostly irreversible. After the virus has attached itself to the cell membrane, it is believed that it enters its nucleic acid into the cell in two ways: it could be through the formation of some kind of a pore in the membrane and the material is then injected through this pore into the cell plasma of the host human being.
The other theory postulates that the virus link up and taken by the endocytosis that is mediated by receptor (Mueller, Wimmer and Cello, 2005). Recent developments have backed the latter argument. As the virus moves from the mouth, it multiplies through the throat up to the gastrointestinal tract before joining into the bloodstream from where it is transported to the. Here, it replicates to overwhelming numbers before starting the process of destroying the cells of the motor neuron (http://american history. si. edu/polio/virusvaccine/how. htm).
This makes them very dangerous since it these motor neurons that control the muscles responsible for respiration, swallowing, circulation, and legs, trunk, and arms. Reasons for the preference of these motor neurons still remain a mystery (http://americanhistory. si. edu/polio/virusvaccine /how. htm). Once the virus has penetrated inside, it takes control of the process of cell assembly and then is able to produce copies of itself, thousands of copies in as little as one hour. In the process, it ends up killing that particular cell before spreading to the others (http://americanhistory. si. edu/polio/virusvaccine/how. htm).
From the gastrointestinal cells where the virus usually divide, it spreads to the follicular dendritic cells in the tonsils, mesenteric and cervical lymph nodes, as well as the intestinal lymphoid tissue before being taken in by the bloodstream (Yin-Murphy and Almond 1996). The presence of these viruses in the blood system, otherwise referred to as viremia, facilitates a great deal the distribution of the virus inside the body where they can survive for periods of up to 17 weeks (Yin-Murphy and Almond, 1996). The virus can also replicate in such areas like tissues of the reticuloendothelial, brown fat and muscles (Sabin, 1956).
Fig 1: Shows how the Poliovirus attacks a Nerve Cell Source: http://americanhistory. si. edu/polio/virusvaccine/how. htm The virus can easily survive in raw sewage, body or fresh water systems. Moreover, they are predominant in places where raw sewage enters directly into a water source without first being treated. The virus can either be transmitted through direct person to person contact or indirectly through getting into contact with materials that do contain the virus like saliva, contaminated water and or sewer, and or feces (http://www.
brown. edu/Courses/Bio_160/Projects1999 /polio/polweb. html). Mostly, people suffering from this virus show little or no signs at all. Other however, may express some short term signs like fever, headache, and general tiredness of the body as well as some pain in the muscles. Others may experience some kind of stiffness in the back and neck. In situations where the virus affects the brain nerves, there can be paralysis of the muscles responsible for breathing and swallowing.
On the other hand, when the spinal cord nerves are invaded, it can result into the legs, arms and or trunk being paralyzed. These symptoms may begin to express themselves after the incubation period that takes between one to two weeks from the time of exposure to the virus (http://www. dhpe. org/infect/polio. htm). Other symptoms include weakness of the muscles, poor temper control constipation and bloated feeling especially in the abdomen. Drooling, abnormal sensation as well a difficulty while starting urinate (Kenneth, 2008)
Treatment of the disease involves a concerted effort to control the symptoms themselves as the disease goes on to infect other areas. It is therefore not possible to wholly treat the disease. In cases of severe attack, some supportive care can be provided. These may include breathing help. In the process of tackling the symptoms, the treatment approach is purely based on the severity of the symptom. They may include providing antibiotics to treat the infections along the urinary canal, supplying pain killers to lower the effects of headache, pains in the muscles as well as spasms.
The patient may also be supplied with medication so as to treat the problem of urinary retention (Kenneth and Wener, 2008). As it is always said, prevention is better than cure; and because once the disease strikes, it can never be cured; researchers have worked around the clock to come up with vaccines for the same. It has been established that once administered, there is 90% chance of not being attacked by the poliovirus. This is usually done on children under the age of five years, who are at a very high risk of contracting the disease. References
http://americanhistory. si. edu/polio/virusvaccine/how. htm Retrieved on 13th December, 2008 http://www. brown. edu/Courses/Bio_160/Projects1999/polio/polweb. html Retrieved on 13th December, 2008 http://www. umm. edu/ency/article/001402all. htm. Retrieved on 13th December, 2008 http://www. polioeradication. org/disease. asp . Retrieved on 13th December, 2008 Kenneth M. and Wener, MD, (2008, January). Department of Infectious Diseases, Lahey Clinic, Burlington, MA. Review provided by VeriMed Healthcare Network. Available online at http://www.
umm. edu/ency/article/001402all. htm. Retrieved on 13th December, 2008 Mueller S, Wimmer E, Cello J (2005). “Poliovirus and poliomyelitis: a tale of guts, brains, and an accidental event”. Virus Res 111 (2): 175–93. Doi: 10. 1016/j. virusres. 2005. 04. 008. PMID 15885840. Ohri, Linda K. ; Jonathan G. Marquess (1999). “Polio: Will We Soon Vanquish an Old Enemy? “ Drug Benefit Trends 11 (6): 41–54. http://www. medscape. com/viewarticle/416890. Retrieved on 13 December, 2008. Rogers, M. (2007), “Health and Fitness” http://www.
answerbag. com/q_view/166253 . Cited on 13th December, 2008 Sabin A (1956). “Pathogenesis of poliomyelitis; reappraisal in the light of new data”. Science 123 (3209): 1151–7. Doi: 10. 1126/science. 123. 3209. 1151. PMID 13337331. Retrieved on 13th December, 2008 Yin-Murphy M, Almond JW (1996). “Picornaviruses: The Enteroviruses: Polioviruses”. Baron’s Medical Microbiology (Baron S et al, Eds. ) (4th ed. ed. ), Univ of Texas Medical Branch. pp. e-text. ISBN 0-9631172-1-1. http://www. ncbi. nlm. nih. gov/books/bv. fcgi?