Polio is a paralytic disease caused by a short, single-stranded RNA virus. Poliovirus is currently found as 2 serotypes in nature: Wild PolioVirus Type1 (WPV1), and Wild PolioVirus Type 3 (WPV3), [Type 2 has been eliminated globally].
In nature, poliovirus causes poliomyelitis* only in human beings. In less than 1% of poliovirus infections, acute flaccid paralysis (AFP) of one or more limbs or chest, or both develops, usually in children.
An infected person harbors the virus in the intestines, passing virions in the feces, promoting fecal-hand-oral transmission of the disease. Oral-hand-oral spreading is also possible, from infected respiratory material or saliva.
Poliovirus is highly contagious. An infected person who enters his home transmits polio infection at a rate of nearly 100% to susceptible children and 90 percent of susceptible adults.
The time from viral exposure to onset of symptoms-the incubation period-is 7 to 14 days. Over 95% of people with a new poliovirus infection have only mild symptoms, such as low-grade fever and malaise, without AFP, but are contagious, shedding poliovirus for months.
As it replicates in the new host, the virus enters the blood stream from the intestines, circulating.
On cell membranes in the body, the neurotropic poliovirus attaches itself to a specific protein: human poliovirus receptor, a member of the immunoglobulin superfamily, occurring in brain, spinal cord, and other organs.[1]
In the nervous system of those predisposed, attachment of poliovirus to immunoreceptors in the spinal cord causes inflammation and destruction of gray matter cells. These cells in health transmit impulses to muscles, especially in the legs, allowing, for instance, walking.
Acute poliomyelitis may damage or destroy these gray matter cells leading to paralysis of leg muscles, sometimes arm muscles, and rarely muscles of respiration, where life-threatening respiratory failure may occur. AFP is a marker of new onset poliomyelitis, which is confirmed by stool analysis for the virus.
Supportive care and rehabilitation, leg braces, crutches, and wheelchairs may be needed long term. Paralysis of the legs may leave children and youths permanently in a form of “crawling” locomotion, with contractures of the hips, withered legs, callused and contracted knees (See Figure 1), and equinus deformities of the ankles and feet, witnessed yet in endemic** countries.
Preventive vaccination requires three or more doses of live attenuated virus administered by mouth or of killed virus administered by injection.
The history of poliomyelitis is quite interesting.✝ A global effort has been pushing toward eradication of poliomyelitis from the face of the earth.✠
References:
[1] Instituut voor Tropische Geneeskunde www.itg.be/…/17_Poliomyelitisp3.htm
[2] N. Engl. J. Med. 2013;368:58-59.
[3] MMWR March 30, 2001 / 50(12);222-4
[4] www.polioeradication.org
*Etymology of “Poliomyelitis:” polio = gray, myelitis = inflammation of the spinal cord, hence poliomyelitis = inflammation of the gray matter of the spinal cord.
**Endemic: belonging to a people, prevalent in a particular nation, as with an endemic disease.
✝ History of Polio
3700 BC: Egyptian mummy found dating to this time with signs of polio.
1580 BC: Priest Ruma with withered leg and equinus foot, depicted in metal plaques, showing signs of polio.
1789: Michael Underwood described debility of the lower extremities of English
children, the first recognizable cases of poliomyelitis.
1834: First epidemic of poliomyelitis on the island of St. Helena.
1843: First outbreaks in the United States reported.1855: Duchenne first describes the pathologic process of poliomyelitis involving the anterior horn cells of the spinal cord.
1908: Transmission of poliomyelitis to a monkey by Landsteiner.
1909: Passage of the virus through a monkey by Flexner.
1949: Growth of the virus in tissue culture.
1951: Three types of poliovirus isolated and identified.
1952: Paralytic polio cases peak at 21,000 in the United States.1954: First large scale trial of Salk (dead vaccine) by injection.
1958: First general use of Sabin (live attenuated vaccine) by mouth, followed by
rapid decline in polio cases in the US.
1979: Last case of wild type polio seen in US.
1988: World Health Assembly of WHO resolves to eradicate polio by 2000.
1999: Last case of poliovirus type 2 recorded.
2000: 3 WHO regions (the Americas, Western Pacific, and Europe) certified polio-free, and poliovirus type 2 declared globally eradicated. Polio types 1 (the most virulent), and 3 remain in Asia and Africa.[2,3]
✠ Global Polio Eradication Initiative
India, as of January 9, 2013, has seen no child paralyzed by wild poliovirus for 2 years, a country once considered the most complex challenge to polio eradication.[4]
Response to Niger outbreak: First immunization activities start in Niger on January 15, 2013, in close coordination with Nigeria-the outbreak is due to imported wild poliovirus in 2012 of Nigerian origin.
73 public health experts from 41 countries are taking part in Stop Transmission of Polio (STOP) training from January 17-18, 2013, in Atlanta, USA. STOP participants are trained in polio eradication strategies and operations; these new participants will join 111 experienced ‘STOPpers’ to be deployed to work closely with national Ministries of Health in countries with a shortage of public health staff skilled in polio eradication.
The WHO (World Health Organization) reports as of January 10, 2013, to date for 2012, 55 cases of type 1 polio, and 3 cases of type 3 in Pakistan; 37 cases of type 1 polio in Afghanistan; 102 cases of type 1 and 19 of type 3 in Nigeria; 5 cases of type 1 in Chad, and 1 case of type 1 in Niger. These numbers have improved from 2011, except for Nigeria.
Total Wild Polio Virus Cases in the World in 2011 = 650
Total Wild Polio Virus Cases in Endemic Countries in 2011 = 341
Total Outbreak Wild Polio Virus Cases in 2011 = 309
Total Wild Polio Virus Type 1 Cases in the World Year 2012 to date (as of 01/10/2013) = 200
Total Wild Polio Virus Type 3 Cases in the World Year to Date 2012 = 22
Total Wild Polio Virus Cases in the World Year to Date 2012 = 222
Total in Endemic Countries to Date 2012 = 216
Total Outbreak Cases to Date 2012 = 6
The Global Polio Eradication Initiative is spearheaded by the World Health Organization, Rotary International, the CDC, UNICEF, and supported by the Bill and Melinda Gates Foundation, and others.
Reference:
- https://www.polioeradication.org
