Poliomyelitis
POLIOMYELITIS
Poliomyelitis, or infantile paralysis, is a highly infectious disease caused by three serotypes of polioviruses. These viruses belong to the Enterovirsus genus of the family Picornaviridae. The infection is transmitted from person to person and rarely produces clinical symptoms. Less than 1 percent of infections will result in paralysis. Death may result, however, especially if respiratory muscles are affected.
Although archeological findings suggest that paralytic poliomyelitis existed before the modern era, the importance of the disease was not recognized until the late nineteenth century. Annual outbreaks of poliomyelitis involving thousands of cases occurred during summer and early fall in various areas of the northern hemisphere during the first half of the twentieth century, making poliomyelitis the leading cause of permanent disability and the cause of numerous premature deaths. The Drinker respirator, also known as the "iron lung," allowed a rapid reduction of poliomyelitis mortality in the 1930s and 1940s.
A major breakthrough in poliomyelitis control took place in 1949, when John F. Enders, Frederick C. Robbins, and Thomas H. Weller developed a tissue culture system for polioviruses. The availability of cultured viruses opened the way to vaccine development. The first poliovirus vaccines were licensed for use in the United States in 1955. These vaccines, developed by Jonas Salk, consisted of formalin-inactivated viruses administered through injections. In 1963, a live oral vaccine, developed by Albert Sabin, was licensed. Within ten years of the introduction of vaccines, the number of poliomyelitis cases decreased by over 95 percent in the United States, and the last case induced by indigenous transmission of wild poliovirus in the United States was detected in 1979. Poliovirus vaccines also allowed rapid declines in disease incidence in Canada, most European countries, Australia, and New Zealand. In Cuba, a two-round mass vaccination campaign in 1962 interrupted poliovirus transmission and rendered the island free of polio.
Most developing countries did not benefit from effective poliomyelitis control before the development of national control programs in the late 1970s. Mass vaccination campaigns, introduced in the Americas during the early 1980s, proved to be an effective means of bringing poliomyelitis under control. The last case of poliomyelitis in the Americas was detected in Peru in 1991, and the western hemisphere was certified as poliofree in 1994.
In 1988, the World Health Assembly launched the Poliomyelitis Eradication Initiative, with a goal of terminating the circulation of wild polioviruses by the year 2000. This worldwide effort relies on three main strategies: high levels of vaccination through routine programs; supplementary vaccination in the form of national immunization days
and local door-to-door immunization ("moppingup") campaigns; and surveillance and investigation of all cases that resemble acute poliomyelitis (acute flaccid paralysis). From 1988 to 1999, the global number of estimated poliomyelitis cases decreased from 350,000 to 20,000.
An important benefit of achieving the Poliomyelitis Eradication Initiative goal will be the discontinuation of poliovirus vaccination. Stopping vaccination will require certifying all areas of the world to be free of wild poliovirus. It will also be necessary to ensure that all infectious and potentially infectious material are contained in maximum safety facilities and to stockpile enough vaccines to respond to any outbreak that might occur should poliovirus be released intentionally or unintentionally. In this way poliomyelitis eradication would follow the path pioneered by smallpox eradication.
PATRICK L. F. ZUBER
(SEE ALSO: Communicable Disease Control; Immunizations; Smallpox)
