Polio Research Paper

Microbe Report: Polio

Stephanie May

Microbiology

Poliomyelitis is a life-changing, sometimes deadly disease caused by the poliovirus. This virus, spread through human feces, once paralyzed many, including US President Franklin Delano Roosevelt, leaving some of its victims trapped in an iron lung for the rest of their lives, and even killing many. A vaccine against this virus was developed by Jonas Salk in the 1950s, and polio infections have dropped tremendously, with the Americas being declared polio-free in 1994 by the World Health Organization1. Efforts are underway to eradicate this deadly disease by the year 2018.

Poliovirus is an enterovirus, which is a genus of positive-sense single-stranded RNA viruses. Positive-sense single-stranded

RNA viruses are able to replicate their genetic material directly using the ribosomes of the host cell. Enteroviruses inhabit the gastrointestinal track and can tolerate acidic environments2. Poliovirus contains a capsid. There are three different serotypes of the poliovirus, and each serotype has a slightly different capsid protein, which makes each serotype specific to different receptors on the host cell. Immunity to one serotype does not produce immunity to the others, which is referred to as minimal heterotypic immunity2.
The poliovirus uses immunoglobulin-like receptors to enter human cells. This virus enters through the mouth and begins replicating in the pharynx and gastrointestinal tract. As the virus moves from the throat through the gastrointestinal tract, it may enter lymphoid tissue and spread to the central nervous system through the bloodstream. When this happens, the patient may become ill with poliomyelitis7.

Most poliovirus infections are asymptomatic. The patient sheds the virus with no symptoms and likely does not even realize that he or she was infected. In about 4% to 8% of polio infections, symptoms are minor and include sore throat, fever, nausea, and vomiting. These symptoms are the same as those of many other viruses, and the patient usually makes a full recovery within a week to 10 days. In about 1% to 2% of polio infections, the patient experiences nonparalytic aseptic meningitis, which creates stiffness in the neck, back, and legs. With this type of infection, the patient usually makes a full recovery in about two to ten days. In less than 1% of polio infections, the patient experiences paralysis, called paralytic poliomyelitis. In one in 200 cases of paralytic poliomyelitis, the patient will become irreversibly paralyzed. About 5% to 10% of those paralyzed will die when their breathing muscles becoming paralyzed1. When examining a patient for polio, a health care provider will look for abnormal reflexes, back stiffness, and a stiff neck. Cultures of the throat, stools, or spinal fluid may also be taken. Antibody testing for the poliovirus may need to be done, and a spinal tap may need to be performed7.
There are three subtypes of paralytic poliomyelitis: spinal polio, bulbospinal polio, and bulbar polio.

Spinal polio, which accounts for about 79% of all cases, is the most common form of paralytic poliomyelitis. In spinal polio, the virus invades the motor neurons of the grey matter of the spinal column. The grey matter is responsible for movement of trunk, limb, and intercostal muscles. As the virus destroys the spinal neurons, the patient loses control of the affected muscles, resulting in paralysis. Usually, paralysis is limited to one side, but sometimes, the patient will experience paralysis on both sides of his or her body. Bulbar polio, which makes up about 2% of the cases of paralytic polio, destroys the neurons in the bulbar region of the brain. This hinders the activity of cranial nerves V (Trigeminal), VII (Facial), IX (Glossopharyngeal), X (Vagal), and XI (Accessory). This causes the patient to experience difficulty breathing, speaking, swallowing, chewing, and the patient may have an abnormal respiratory rate and heart rhythm. Complications of bulbar polio include pulmonary edema and shock. Bulbospinal polio accounts for about 19% of all paralytic poliomyelitis cases. In bulbospinal polio, the virus affects both the bulbar region of the brain and the grey matter of the spinal column. In this subtype of paralytic poliomyelitis, the nerves of cervical vertebrae C3-C5 are affected. The phrenic nerve is part of this plexus, and since this innervates

the diaphragm, it may leave the patient unable to breathe without the help of a ventilator8.
Negative pressure ventilators, commonly known as iron lungs, have been used to keep those whose breathing muscles have been paralyzed alive. The negative pressure ventilator helps to force the negative pressure required for breathing when muscles have been paralyzed. Negative pressure ventilators were developed in 1927 by Drs. Philip Drinker and Louis Agissiz Shaw at Harvard University. Prior to this invention, most patients died when breathing muscles became paralyzed9. There are still seven people in the United States living in the iron lung, including Paul Alexander, now a lawyer, who has been living in an iron lung since he was paralyzed by polio in 1952 at the age of six4.

Post-polio syndrome affects some people for years after becoming ill with polio. Symptoms include progressive muscle and joint weakness and pain, fatigue, muscle atrophy, breathing and swallowing problems, and sleep-related breathing disorders such as sleep apnea5. Unlike polio, post-polio syndrome is not contagious. The only people affected by post-polio syndrome are polio survivors. The exact cause of post-polio syndrome is unknown, but some theories do exist. One theory suggests that the nerve cells were overworked during the course of the polio, while another suggests that poliovirus can potentially cause brain damage. To be diagnosed with post-polio syndrome, the patient must have experienced paralytic poliomyelitis with evidence of motor neuron loss, have a period of recovery after the paralytic poliomyelitis, and experience progressive and persistent muscle weakness or decreased endurance, all of which must be present for at least a year. In addition, other illnesses must be ruled out before making a diagnosis of post-polio syndrome. Currently, there is no effective medical treatment for post-polio syndrome. Patients with post-polio syndrome may experience relief from symptoms with lifestyle changes and should talk with their physician about their condition6.

The first polio vaccine was developed by Dr. Jonas Salk in 1952, and it was licensed in 1955. An oral vaccine was developed by Dr. Albert Sabin in 1957 and was licensed in 1962. The injectable vaccine contains an inactivated form of the poliovirus, and the oral vaccine contains a weakened form of the virus3. Dr. Salk’s injectable vaccine provides highly effective immunity for both poliovirus types 2 and 3. It is less effective at protecting against poliovirus type 1. In 1987, another modified polio vaccine became available that offered greater protection against poliovirus type 1. This is the vaccine that is currently in use today. The live oral polio vaccine has been known to cause vaccine-associated paralytic polio in one per 2.4 million doses. People over 18 years old and immunocompromised children are far more likely to acquire vaccine-associated paralytic polio. In the United States, most children receive the inactivated injectable vaccine for this reason2. Children in the US should be vaccinated against polio at two months, four months, between six and 18 months, and between ages four and six before entering school. Most adults are not given polio vaccines as most already have immunity against polio. Only some adults who are at high risk for polio will receive a booster shot. High-risk adults include those who are immunocompromised, such as HIV patients, and those who are traveling to an area of the world where polio is still endemic5.

The World Health Organization has set a goal of eradicating polio by the year 2018.

The polio vaccine has helped lower polio rates tremendously since the 1980s. In 1988, there were about 350,000 cases of polio. This number decreased 99% to 416 cases of polio in 2013. The last case of naturally occurring polio in the US occurred in 1979, but polio is still endemic, or commonly found, in Afghanistan, Pakistan, and Nigeria1. The figure below from the United States Center for Disease Control shows the profound impact that the polio vaccine has had on polio rates. As is snown, when the inactivated vaccine was approved in 1955, poliomyelitis rates

plummeted2.

Once a public health nightmare, polio is well on its way to becoming an disease of the past, thanks to vaccines and the work of the World Health Organization with its plan to eradicate polio by the year 2018. While this disease does not present with symptoms in all of its hosts, it has had a profound impact on the lives of those left paralyzed, those who have lived their lives in iron lungs, and those who it has killed.

1. World Health Organization Poliomyelitis Fact Sheet. Updated October 2014. http://www.who.int/mediacentre/factsheets/fs114/en/
2. Centers for Disease Control Polio Vaccine Fact Sheet. http://www.cdc.gov/vaccines/pubs/pinkbook/polio.html
3. Polio vaccine—Wikipedia. http://en.wikipedia.org/wiki/Polio_vaccine
4. “The Man in the Iron Lung.” 1 Dec 2014. Barry Hoffman. MedicineNet. http://www.medicinenet.com/script/main/art.asp?articlekey=185514
5. Mayo Clinic Diseases and Conditions. Polio. Updated May 11, 2014. http://www.mayoclinic.org/diseases-conditions/polio/basics/definition/con-20030957
6. National Institute of Neurological Disorders and Stroke. Post-Polio Syndrome Fact Sheet. Last updated February 23, 2015. http://www.ninds.nih.gov/disorders/post_polio/detail_post_polio.htm
7. MedlinePlus Medicine Encyclopedia. http://www.nlm.nih.gov/medlineplus/ency/article/001402.htm
8. Wikipedia. Poliomyelitis. http://en.wikipedia.org/wiki/Poliomyelitis
9. NMAH. Polio: The Iron Lung and Other Equipment. http://amhistory.si.edu/polio/howpolio/ironlung.htm
10. Poliovirus – Wikipedia. http://en.wikipedia.org/wiki/Poliovirus
11. “The Symptoms and Progression of Polio Infection.” Boston University Medical Center. Last updated December 12, 2013. http://sphweb.bumc.bu.edu/otlt/MPH-Modules/PH/Polio/Polio_NEW3.html