Poliomyelitis

Updated: Feb 03, 2016
  • Author: Srinivasa Vidyadhara, MBBS, MS, DNB; Chief Editor: Jeffrey D Thomson, MD  more...
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Overview

Background

Poliomyelitis is first known to have occurred nearly 6000 years ago, as evidenced by the withered and deformed limbs of certain Egyptian mummies. It was not until the 1950s that a vaccine became available.

Since May 1988, when the World Health Assembly resolved to eradicate poliomyelitis, the estimated global incidence of polio has decreased by more than 99%, and three World Health Organization (WHO) regions (the Americas, the Western Pacific, and Europe) have been certified as polio-free. Since 1994, when the countries of the WHO South-East Asia Region (SEAR) began accelerating polio-eradication activities, substantial progress toward that goal has been made.

Problems remain due to the difficulties involved in extending immunization coverage to some regions (especially Africa), integrating new vaccines into routine immunization schedules, and securing sufficient funding for programs. Injection safety is also a major problem that should be resolved by utilization and proper disposal of single-use autodisabling syringes. The forthcoming availability of new vaccines and the action of the Global Alliance for Vaccines and Immunization hold reasonable hope for the future. Other problems remain, such as new conditions resembling polio paralysis caused by viral infection other than by poliovirus 2 and postpolio syndrome (PPS).

It is safe to assume that acute and residual poliomyelitis is still encountered in the developing world. In developed countries, on the other hand, residual poliomyelitis is still occasionally seen in the elderly and immigrants. [1, 2, 3, 4, 5, 6, 7, 8]

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Pathophysiology

Poliovirus is spread by the fecal-oral route and by aerosol droplets. The poliovirus is shed in oral secretions for several weeks and in the feces for several months. The poliovirus destroys the anterior horn cells in the spinal cord.

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Etiology

Acute poliomyelitis is caused by small RNA viruses of the Enterovirus genus of the Picornaviridae family. The single-stranded RNA core is surrounded by a protein capsid without a lipid envelope, which makes poliovirus resistant to lipid solvents and makes it stable at a low pH. Three antigenically distinct strains are known, with type 1 accounting for 85% of cases of paralytic illnesses. Infection with one type does not protect from the other types; however, immunity to each of the three strains is lifelong.

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