What is Polio?

Polio (also known as Poliomyelitis)

An infectious disease that can be transmitted from person to person. Polio is caused by poliovirus, an enterovirus. Poliovirus is most well known for causing paralysis in young children.[0]

Poliovirus is part of the picornavirus viral family, a taxonomic grouping that includes other familiar viruses such as the rhino virus and hepatitis A virus. These viruses are most known for their icosahedral capsid(20 faces) structure that lacks a viral envelope and carries the positive-sense single stranded RNA genome. Further characteristics include being able to withstand low pH and thus able to pass through the stomach to infect and replicate in the intestinal epithelial cells and being incredibly infectious through the fecal-oral route. [0]

*funfact: Humans are the only natural hosts of this disease. Chimapanzees, Green African Monkeys etc can only be experimentally infected.

Whilst most infections are asymptomatic, viral particles that gain entrance into the central nervous system can replicate in neurons and destroy cells that govern muscle function resulting in flaccid paralysis.[0] To simply put it, the poliovirus invades the brain and spinal cord and may cause paralysis. However, 72 out of 100 infected people will not have any visible symptoms.[1]

Symptoms commonly include:
-Sore throat
-Fever
-Feeling lethargic
-Nausea
-Headache
-Stomach pains

More severe symptoms include:
-Paresthesia ( pins and needles in arms and legs or both)
-Meningitis (Inflammation of the brain & spinal cord)
-Paralysis or weakness of arms and legs

*Paralysis may be fatal due to the inactivation of muscles that aid in respiration. Hence Polio is often referred as a paralytic infection.

Poliovirus is easily transmitted through contact with an infected person. The virus lives in the infected person's throat and intestine. It enters the body though contact of feces and though less common, sneezes and coughs. Contamination of everyday items after not properly washing after using the toilet may speed up the infection rate. This is especially so in rural countries living in unsanitary conditions.

*The poliovirus may be cured with Oral Poliovirus Vaccine(OPV) or Inactivated Poliovirus Vaccine(IPV) but there are cases of Post-polio syndrome where patients recover after a vaccination but there happened to be a relapse of the patient's previous condition. [1]

Reference:
[0]Poliomyelitis. (n.d.). Retrieved July 31, 2015, from https://microbewiki.kenyon.edu/index.php/Poliomyelitis
[1] What Is Polio? (2014, October 15). Retrieved July 31, 2015, from http://www.cdc.gov/polio/about/

The Problems of Polio Today

How does Polio affect the world..? Is it still an issue today?
There are vaccinations that eradicate Polio which are recommended worldwide to young children and some adults. However, there are cases of Polio in some countries despite having vaccines available. Why is that..? The most likely case of such happening is due to wild polioviruses that occur naturally as well as vaccine-derived Polio(cVDPV).

What is Vaccine-Derived Polio (cVDPV)?

Vaccines for Polio such as the Oral Poliovirus Vaccine(OPV) contains weakened or attenuated vaccine-virus which activates the immune responses in the body. When such vaccines are given to a young child, the attenuated vaccine-virus replicates in the intestines and allows the child to develop an immunity against this virus by producing antibodies. During this period, the vaccine-virus will also be excreted. Excretion of this vaccine-virus may spread to the community and offer "passive" immunization to the community children before eventually "dying out".

On some extremely uncommon circumstances, should a community be severely under-immunized, the excretion of the vaccine-virus may continue to circulate for an extended time. The longer the vaccine-virus is allowed to circulate, the chances of a genetic change occurring for the virus increases. This may cause the virus to genetically modify itself to be able to paralyze despite being in a weakened form initially.

It takes an incredibly long period of time, around a year or so, for such an instance to occur and a highly under-immunized community as a background setting is required. Circulating cVDPV occur in areas where routine or supplementary immunization activities are poorly conducted and a population is left susceptible to the disease.

If a population is fully immunized and lives in a well sanitized environment, they will not experience both vaccination-derived polio and wild polioviruses, [3]

Reference:
[3]What is vaccine-derived polio? (2014, October ). Retrieved May 27, 2015, from http://www.who.int/features/qa/64/en/


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