Poliomyelitis

Poliomyelitis is an acute infectious disease due to a virus which attacks the nervous system, primarily the anterior horn cells of the spinal cord and brain-stem. The usual route of infection is the alimentary tract via personal contact with healthy carriers and abortive cases and via the faecal contamination of food. The disease is characterized by symptoms ranging from a mild nonparalytic infection to an extensive flaccid paralysis of voluntary muscles.

Mild cases of polio may last only a few days and may cause the person to have a fever, sore throat, stomach ache, and headache.  Children and adults who get a serious case of polio become paralyzed. They may be crippled or even die from the disease. 

There is evidence that the disease has existed for many centuries. However, the first clear description of poliomyelitis came from Jakob von Heine in 1840. It was not recognized in its epidemic form until Oskar Medin in 1887 reported observations on an outbreak in Sweden. In addition to the usual spinal form, he described the bulbar and certain less common types of the disease. C S Caverly, in 1896, recognized that the disease may occur in an abortive or nonparalytic form, a fact confirmed by others later.

Since then severe epidemics have been reported in many countries and islands including North, Central and South America, Europe and Africa. The disease reached epidemic proportions in some region of the USA almost every year after the beginning of the 20th century until vaccine became available. The greatest recorded sustained incidence in the USA was in 1942-43; in 1950 there were 33,344 cases in the USA. In 1952 severe epidemics occurred in Denmark, Germany and Belgium. In Asia, outbreaks were reported in Bombay, Singapore, Japan, Korea and the Philippines.

The global elimination of polio is technically feasible and is targeted as one of the six vaccine-preventable diseases by the WHO's Expanded Programme on Immunizations. The aim of the WHO was to eradicate polio by the year 2000. It is claimed that polio can be eradicated if an entire population is vaccinated on the same day, and the vaccination is repeated 3 more times at monthly intervals, as done in Brazil. The virus cannot live for more than a few weeks outside the body. Even in war, the warring parties have agreed to stop for long enough to allow blanket immunization. The greatest hindrance to its eradication is the cost. While the cost of each vaccine is pennies, when other costs are included it was estimated that about $800 million was needed to complete the global vaccination campaign.

Polio occurs most often in summer and fall and generally attacks children under five years of age. In 1995, it was claimed that 100,000 children a year are crippled by it. Previously, the World Health Organization estimated that 220,000 children were paralysed, and 23,000 killed, by polio every year in developing countries.

Since the widespread introduction of vaccination against poliomyelitis, around 1957, the incidence of this disease has fallen to insignificant proportions in North America, parts of Europe, and several countries in other parts of the world; in 1968 there were only 24 cases in England and Wales, compared with 3,200 in 1956. In Sweden and Finland, paralytic poliomyelitis has disappeared following immunization programmes with multiple doses of inactivated vaccine that covered close to 100% of the population. Polio can however return to countries from which it was previously eradicated, as happened in 1992 in a Dutch religious community opposed to immunization.

Although there have been no recent cases of polio reported in the Western Hemisphere, there are still thousands of polio cases each year in many developing countries in Africa, Asia, the Middle East, and Eastern Europe. India has 60% of the world's polio cases. In 1996, 155 countries reported no cases of polio, 18 countries had one case, and 27 countries reported more than 10 cases. 14 countries did not submit reports.

In large areas of Africa, Asia and Latin America the incidence appears to have been rising disconcertingly during recent years, and large outbreaks are being reported there with increasing frequency. In many tropical countries paralytic poliomyelitis is a far more common disease than has been appreciated.