History And Definition Of The Poliomyelitis Virus Biology Essay

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Poliomyelitis has plagued humans for many centuries and continues effecting people to date in developing countries even though a vaccine has been available for over fifty years. Michel Underwood, a British doctor, in 1789 was the first to formally define Polio in a clinical sense (NMAH, 2007). He first described Poliomyelitis as debility of the lower extremities in his children patients (CDC, 2007). It was originally thought to be heavy metals or a bacterium as the underlying cause of the disease.

It was discovered in 1908 by Karl Landsteiner and Erwin Popper to actually be a virus (NMAH, 2007). The two scientists proved that it was a virus with diseased spinal tissue and monkeys as their test subjects (Vaccinations, 2006). They blended a solution of water and the diseased tissue together and then directly inserted the mixture into the brain of a pair of monkeys (Vaccinations, 2006). As a result the first monkey did not survive testing and the second was paralyzed from the virus (Vaccinations, 2006). However, to confirm their hypothesis, the two scientists dissected their test subjects and found that each monkey suffered from the same affliction as the original human tissue donor (Vaccinations, 2006).

The first recorded outbreaks of the virus occurred in Europe during the early 19th century which then found its way to the United States in 1894 (CDC, 2007). The first outbreak occurred in Vermont with 132 cases (Timeline, 2007). From there the disease spread rapidly effecting large cities as well as rural areas. Epidemics were occurring at alarming rates with 13,000 to 20,000 paralytic cases reported each year (CDC, 2007). Even the 32nd president of the United States Franklin Delano Roosevelt, FDR, contracted the disease at the age of 39 showing just how widespread and serious the situation had become (Timeline, 2007).

FDR being a very public image was very open about having Polio to the American public, but not wanting to be considered weak he lied about the extent of his condition (Timeline, 2007) FDR may have had contracted polio but it did not slow him down as a president. He helped the nation recover from the Great Depression, get through World War II, founded the March Of Dimes, and in total FDR served four terms as the president of the United States (Roosevelt, 2007). The March of Dimes is a foundation that was setup by FDR for infantile paralysis that is still present to date. Sadly, however, FDR did not live to see all of his contributions for a Polio cure or prevention method become reality. FDR died in 1945 and the vaccine for polio was developed in 1952 (Timeline, 2007). However after Phase III clinical trials the vaccine was released to the public ten years to the day after his death on April 12, 1955 (Timeline et al Roosevelt, 2007).

The introduction of Dr. Salk's new killed virus vaccine dropped reported cases of Polio in the U.S. by 50% within the first two years (CDC, 2007). This was mainly due to the fact that Dr. Salk did not want to gain financially from vaccine and never patented it (Watson, 2007). The vaccine was produced by six major drug companies by order of the Federal Government plan and released to masses where Dr. Salk was referred to as a miracle worker (Watson et al Polio Vaccine, 2007). A few years later Dr. Albert Sabin developed a live attenuated vaccine which proved to be more effective because it stimulated both an antibody response along with B-memory cells which was given orally (Timeline et al CDC, 2007).

With the new oral vaccine now in place the last known reported 'wild type' Polio virus case was in 1979 (Timeline, 2007). This was chosen over Dr. Salk's vaccine because it provided better protection and it was cheaper to produce. Armed with the new vaccine the World Health Organization, WHO, started a program to eradicate to the Polio Virus in every country to which they are still fighting today with over 80% of the world Polio free (Figure 1 and 2).

Polio Virus

Poliomyelitis is a highly contagious disease that lives mainly in the intestinal tract and in feces of an infected person (Polio, 2007). There are two categories of Poliomyelitis: Nonparalytic and Paralytic (Polio, 2007). The virus is spread by contact with infected feces or in food and water supplies (Polioeradication, 2007). Polio, upon infection, then replicates in the gastrointestinal tract and in the throat where it enters the bloodstream (Polio, 2007). The replication cycle for the virus involves many steps and the whole process can happen without the presences of a nucleus (Blackwell, 2004). First the virus enters the cell through receptor-mediated endocytosis and hydrogen ions are pumped into the vesicle removing the coat proteins in a specific order (Blackwell, 2004).

Then the positive-sense RNA is translated into large polyproteins since this strand is most like the host mRNA (Blackwell, 2004). Then viral replicase is released from a precursor protein that mediated in the production of more mRNA, but this is not like the host's original mRNA (Blackwell, 2004). The host no longer produces any of it own proteins because the virus has basically hijacked the system so that only the viron proteins are made (Blackwell, 2004). The newly synthesized RNA with a mixture of VPg proteins at the 5' end result in the capsid maturing when the viral genome enter (Blackwell, 2004).

This process is continued repeatedly in the cell cytoplasm until lysis or cell death occurs causing the virus to be released (Blackwell, 2004). The virus capsid forms when the precursor proteins bind to form promoters, and then the promoters assemble as pentamers (Blackwell, 2004). A total of twelve of these come together to assemble a procapsid which the viral RNA is incorporated, and the capsid is matured by cleaving certain VP proteins (Blackwell, 2004)(Figure 3). Once it enters the bloodstream the virus is then carried throughout the body where it attacks the spine and brain that may cause paralysis (Polio, 2007). It can do this because motor neurons also have receptors for the poliomyelitis virus (Blackwell, 2004).

The Baltimore Classification system categorizes Poliovirus as a Class IV positive single-stranded RNA virus in which it is a nonenveloped Picornavirus because it needs to be translated because the viral RNA is oriented the same as the host mRNA (Wagner, 2004). The virus has three different serotypes: 1, 2, and 3. Serotype 3 was used in Albert Sabin's oral vaccine because it is the most prevalent cause for paralytic poliomyelitis (Blackwell, 2004). It contains 7 anti-parallel beta sheets along with 11 alpha helices (Figure 4). The serotype 3 for the Polio virus contains 5 different chains with a hydrophobic core and hydrophilic outer layer (Figure 5).

Symptoms and Treatment

A person can be infected with Poliomyelitis and not show symptoms of having the disease (Polio, 2007). There are two forms of Poliomyelitis as mentioned in the above section each has common set of symptoms nausea, diarrhea, fever, sore throat, and/or vomiting basically like the flu (Polio, 2007). With the Nonparalytic Poliomyelitis these symptoms usually go away after a week or two (CDC, 2007). But the Paralytic Poliomyelitis causes paralysis in either one side or both sides of the body but less than 1% of those infected develop this version of the disease (Polio et al Polioeradication, 2007). Typically the paralysis is more serve on one side of the body (Figure ). However these individuals are treated with a positive pressure ventilator because without respiratory therapy the disease can be fatal (Polioeradication, 2007). In the 1940's and 50's this technology wasn't available yet so patients were treated with a big metal machine called the Iron Lung (Polioeradication, 2007). This was where the patient was place in a long metal cylinder tube and a positive pressure was placed in the atmosphere around the patient forcing air into their lungs, because the patient may have lost the ability to breathe on their own when paralysis set in (Polioeradication, 2007).

There is no cure for the Poliomyelitis virus once infected (CDC, 2007). There is only supportive treatment where the patient is made as comfortable as possible (Polio, 2007). When the patient recovers from the virus they are put on a daily exercise plan to strengthen there weak muscles (Polio, 2007). The best way to treat the disease is not to get it at all. The first vaccine that became available was a killed-virus treatment by Dr. Salk (Timeline, 2007). Where the virus was isolated from an infected source, purified, and heated to kill it (Watson, 2007). Then came Dr. Sabin's live attenuated vaccine in which virus can only replicate to a certain point (Blackwell et al CDC, 2007). This vaccine provides more protection because it stimulates both an antibody response and memory cells since the virus can replicate which gives it a longer duration period in the body (Blackwell et al CDC, 2007).

Outlook for a Cure

There is no known cure for Poliomyelitis, so the best way to stop the disease and spread is by preventative measures. If someone does contract the virus the best medicine we have at this time is Therapeutic medicine in which symptoms are treated to the best of ability and the patient is observed until it passes or they are deceased. The oral vaccine has been given to millions of people around the world and has proven to be effective in protecting against the virus. It has even eliminated it from the country all together like the U.S., Canada, U.K., China and other countries. Developing countries however are still having difficulty eradicating the disease like in the U.S. Some countries in Africa and also India are still waging war on the virus. This could be due to lack of resources either to buy the vaccine or even education about the dangers of Polio. Another factor could be that the countries themselves have not made the vaccine mandatory. But Polio eventually will be a disease of the past like smallpox.