12 feb. 2014

Polio is caused by a human enterovirus called the poliovirus. Wild polioviruses are those that occur naturally.

The virus

Polio is caused by a human enterovirus called the poliovirus. Wild polioviruses are those that occur naturally.

The poliovirus consists of an RNA genome enclosed in a protein shell called a capsid. There are three serotypes of wild poliovirus – type 1, type 2, and type 3 – each with a slightly different capsid protein.
Scanning electron micrograph of the wild poliovirus
The wild poliovirus as seen through a microscope. The virus invades the nervous system, causing paralysis in one out of every 200 children.
From GPEI site photo gallery
Type 2 poliovirus has been eliminated in the wild – the last wild type 2 poliovirus was detected in India in 1999. 
In this final stage of polio eradication, only type 1 and type 3 wild poliovirus continue to circulate in endemic areas. Both are highly infectious and both cause paralytic polio. Type 1 is the most pervasive strain of poliovirus, with type 3 highly localized in northern India, northern Nigeria, Pakistan and Afghanistan.






Polio and prevention
Polio is a crippling and potentially fatal infectious disease. There is no cure, but there are safe and effective vaccines. The strategy to eradicate polio is therefore based on preventing infection by immunizing every child until transmission stops and the world is polio-free.
The disease
Polio (poliomyelitis) is a highly infectious disease caused by a virus. It invades the nervous system and can cause irreversible paralysis in a matter of hours.
Indian boy with polio
An Indian boy’s legs are shrunken from paralysis caused by polio
WHO/T. Moran

Who is at risk?

Polio can strike at any age, but it mainly affects children under five years old.

Transmission

Polio is spread through person-to-person contact. When a child is infected with wild poliovirus, the virus enters the body through the mouth and multiplies in the intestine. It is then shed into the environment through the faeces where it can spread rapidly through a community, especially in situations of poor hygiene and sanitation. If a sufficient number of children are fully immunized against polio, the virus is unable to find susceptible children to infect, and dies out.

Young children who are not yet toilet-trained are a ready source of transmission, regardless of their environment. Polio can be spread when food or drink is contaminated by faeces. There is also evidence that flies can passively transfer poliovirus from faeces to food.

Most people infected with the poliovirus have no signs of illness and are never aware they have been infected. These symptomless people carry the virus in their intestines and can “silently” spread the infection to thousands of others before the first case of polio paralysis emerges.

For this reason, WHO considers a single confirmed case of polio paralysis to be evidence of an epidemic – particularly in countries where very few cases occur.

Symptoms

Most infected people (90%) have no symptoms or very mild symptoms and usually go unrecognized. In others, initial symptoms include fever, fatigue, headache, vomiting, stiffness in the neck and pain in the limbs.

Acute flaccid paralysis (AFP)

One in 200 infections leads to irreversible paralysis, usually in the legs. This is caused by the virus entering the blood stream and invading the central nervous system. As it multiplies, the virus destroys the nerve cells that activate muscles. The affected muscles are no longer functional and the limb becomes floppy and lifeless – a condition known as acute flaccid paralysis (AFP).

All cases of acute flaccid paralysis (AFP) among children under fifteen years of age are reported and tested for poliovirus within 48 hours of onset.

Bulbar polio

More extensive paralysis, involving the trunk and muscles of the thorax and abdomen, can result in quadriplegia. In the most severe cases (bulbar polio), poliovirus attacks the nerve cells of the brain stem, reducing breathing capacity and causing difficulty in swallowing and speaking. Among those paralysed, 5% to 10% die when their breathing muscles become immobilized.
In the 1940s and 1950s, people with bulbar polio were immobilized inside "iron lungs" – huge metal cylinders that operated like a pair of bellows to regulate their breathing and keep them alive. Today, the iron lung has largely been replaced by the positive pressure ventilator, but it is still in use in some countries.

Post-polio syndrome

Around 40% of people who survive paralytic polio may develop additional symptoms 15–40 years after the original illness. These symptoms – called post-polio syndrome – include new progressive muscle weakness, severe fatigue and pain in the muscles and joints.

Risk factors for paralysis

No one knows why only a small percentage of infections lead to paralysis. Several key risk factors have been identified as increasing the likelihood of paralysis in a person infected with polio. These include:
  • immune deficiency
  • pregnancy
  • removal of the tonsils (tonsillectomy)
  • intramuscular injections, e.g. medications
  • strenuous exercise
  • injury.

    Treatment and prevention

    There is no cure for polio, only treatment to alleviate the symptoms.  Heat and physical therapy is used to stimulate the muscles and antispasmodic drugs are given to relax the muscles. While this can improve mobility, it cannot reverse permanent polio paralysis.

    Polio can be prevented through immunization. Polio vaccine, given multiple times, almost always protects a child for life.
    Related links

    History of polio

    In the early 20th century, polio was one of the most feared diseases in industrialized countries, paralysing thousands of children every year. Soon after the introduction of effective vaccines in the 1950s and 1960s however, polio was brought under control and practically eliminated as a public health problem in these countries.

    It took somewhat longer for polio to be recognized as a major problem in developing countries. Lameness surveys during the 1970s revealed that the disease was also prevalent in developing countries. As a result, during the 1970s routine immunization was introduced worldwide as part of national immunization programmes, helping to control the disease in many developing countries.

    In 1988, when the Global Polio Eradication Initiative began, polio paralysed more than 1000 children worldwide every day. Since then, 2.5 billion children have been immunized against polio thanks to the cooperation of more than 200 countries and 20 million volunteers, backed by an international investment of more than US$ 8 billion.

    Today, polio has been eliminated from most of the world and only four countries remain endemic. In 2009, fewer than 2000 cases were reported for the entire year.

    Use this interactive timeline to trace the history of polio from 1580 B.C. to the present.


    http://www.polioeradication.org/Polioandprevention/Historyofpolio.aspx



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    Post Polio Litaff, Association A.C _APPLAC Mexico

    UCLA gets $6 million to Study new ways to restore hand movement after Paralysis


    The National Institute of Biomedical Imaging and Bioengineering has awarded UCLA researchers Dr. Daniel Lu (Brentwood) and Dr. Reggie Edgerton (Bel Air) a $6 million, five-year grant to explore new therapies for the approximately 273,000 Americans living with spinal-cord injuries. Some 12,000 Americans suffer such injuries each year.
    The UCLA research will focus on restoring hand function to patients paralyzed from the neck down. Cervical spinal-cord injuries—those involving the neck—make up more than half of the cases in the U.S.
    "Spinal-cord injury typically strikes people in the prime of their lives, with nearly half between ages 16 and 30," said Lu, an assistant professor of neurosurgery at the David Geffen School of Medicine at UCLA and a clinician at the UCLA Spine Center. "Currently there are no effective treatments for spinal-cord injury, and the resulting paralysis has been viewed as permanent. We are exploring ways to change that."
    In seeking to help people with cervical spinal-cord injuries regain the use of their hands, the UCLA team is looking to build on findings from Edgerton's earlier work, conducted with Russian scientist Yury Gerasimenko, on lumbar spinal-cord injuries—those to the lower spine.
    "Recovering the ability to use one's hands is a top priority for people with cervical spinal-cord injury," said Lu, who grew up in Palos Verdes. "We aim to restore patients' independence by returning their ability to type on a keyboard, open doors and transfer themselves between their bed and wheelchair."
    The most promising therapy uses electrical impulses to stimulate dormant pathways within the spinal cord, allowing the brain's previously unrecognized signals to reach past the injured area.
    The research team screens candidates by placing an electrode on the person's skin. If the electrical stimulation elicits a positive response, the patient may choose surgical implantation of the electrode under the skin near the spinal injury.
    Lu is testing the stimulation at various power levels, rates and locations to fine-tune the most effective dosage and application, which will be customized to each patient and their injury.
    A second approach will explore drugs to improve function, particularly the off-label use of serotonergic agonists, medications approved by the Food and Drug Administration that are typically prescribed to treat depression.
    Nerve cells communicate in part through the neurotransmitter serotonin. By using drugs that increase serotonin levels within the spinal cord, the researchers hope to open up communication pathways that cells ordinarily wouldn't recognize and to study how this affects patients' ability to use and control their hands.
    "The spinal cord is smart," said Edgerton, a distinguished professor of integrative biology and physiology and of neurobiology at UCLA. "The nerve-cell networks in the spinal cord are capable of initiating movement without any input from the brain. This is partly due to muscle sense, or signals sent from the hands and legs directly to the spinal cord.
    "In other words, the spinal cord can independently interpret sensory feedback and direct the extremities to balance and move with minimal involvement from the brain."
    Provided by University of California, Los Angeles
    This Phys.org Science News Wire page contains a press release issued by an organization mentioned above and is provided to you “as is” with little or no review from Phys.Org staff.
    Post Polio Litaff, Association A.C _APPLAC Mexico

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    México Post Polio Una Vida Un Camino Una Experiencia
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    Post Polio LITAFF A.C.

    www.postpoliolitaff.org/
    Postpoliolitaff.- Asociación Post Polio Litaff A.C Primera Organización oficial sobre Síndrome de Post Poliomielitis En México.


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