The story of polio probably began long ago in the cities of Mesopotamia, Egypt, and Northern India, where the conditions were right for transmission of the virus – chiefly high population density and rudimentary sanitation. It is a story that experts in Public Health believe will end sometime in the next decade with the eradication of poliovirus ­ only the second human virus to have been eradicated, the other being smallpox.

One thing we do know is that polio has been an endemic disease in almost all human societies for thousands of years, although it is only in relatively modern times that epidemics of what was called infantile paralysis have been seen. The first firm evidence of polio that we have are in the wall paintings and bas-reliefs of Ancient Egypt thanks to the passion of that civilisation for recording details of everyday life. It is thought that the Roman Emperor Claudius was stricken as a child, which caused him to walk with a limp for the rest of his life, but perhaps

The earliest recorded case of poliomyelitis is that of Sir Walter Scott who in 1773 developed "a severe teething fever which deprived him of the power of his right leg.” At the time, polio was not known to medicine, but a retrospective diagnosis of polio is considered to be strong due to the detailed account Scott later made. The first clinical description of polio was by British physician Michael Underwood given in 1789, describing it as "debility of the lower extremities,” and in 1840 the German physician Jacob von Heine published a monograph describing the clinical features of the disease, noting that symptoms suggested an involvement of the spinal cord.

Prior to the 20th-century, major polio epidemics were unknown, and polio infections were rarely seen in infants younger than six months of age because of the protective effects of maternal antibody, most cases occurring in children between the ages of six months and four years. Young children who contract polio, generally suffer only mild symptoms, but as a result, they become permanently immune to the disease. However, in developed countries during the late 19th and early 20th centuries improvements were being made in community sanitation, including improved sewage disposal and clean water supplies, and better hygiene meant that exposure to poliovirus was delayed until late childhood or adult life when it was more likely to take the paralytic form. The first published report of multiple cases was in 1843 of an 1841 outbreak in Louisiana. A fifty-year gap occurred before the next US report of a cluster of 26 cases in Boston in 1893, and the first recognised polio epidemic in the US occurred the following year in Vermont with 132 total cases and 18 deaths, including several cases in adults. Numerous epidemics of varying magnitude began to appear throughout the country and by 1907 approximately 2,500 cases of polio were reported in New York City. The first major epidemic was in Brooklyn NYC in 1916 and by the end of the year over 27,000 cases, and more than 6,000 deaths were reported throughout the country with over 2,000 deaths in New York City alone. A similar picture was seen in the United Kingdom peaking between 1946 and 1958 with thousands of cases each year.

The poliovirus is highly contagious and in endemic areas wild polioviruses can infect virtually the entire human population. It is seasonal in temperate climates, with peak transmission occurring in summer and autumn, but seasonal differences are far less pronounced in tropical areas. The time between first exposure and first symptoms, known as the incubation period, is usually 6 to 20 days, with a maximum range of three to 35 days and virus particles continue to be excreted in the faeces for several weeks following initial infection. The disease is transmitted primarily via the feacal-oral route through ingestion of contaminated food or water, but the virus may occasionally be transmitted via the oral-oral route, a mode especially visible in areas with good sanitation and hygiene. Polio is most infectious between seven and ten days before and after the appearance of symptoms, but the transmission is possible as long as the virus remains in the saliva or faeces.

Poliovirus enters the body through the mouth, infecting the first cells with which it comes in contact, first in the pharynx and then the intestinal mucosa. Poliovirus replicates within gastrointestinal cells for about a week, from where it spreads to the tonsils, intestinal lymphoid tissue, and the mesenteric lymph nodes, where it multiplies abundantly. It is subsequently absorbed into the bloodstream where its presence is known as a viraemia, enabling it to be widely distributed throughout the body. In mild cases with no central nervous system involvement viraemia leads to the development of minor influenza-like symptoms. Invasion of the central nervous system is rare, provoking a local inflammatory response, in most cases resulting in a self-limiting inflammation of the meninges, the layers of tissue surrounding the brain, which is known as non-paralytic aseptic meningitis. Penetration of the CNS provides no known benefit to the virus and is quite possibly an incidental deviation of a normal gastrointestinal infection.

Spinal polio is the most common form of paralytic poliomyelitis resulting from viral invasion of the motor neurons of the anterior horn cells, or the ventral gray matter in the spinal column, which is responsible for movement of the muscles, including those of the trunk, limbs, and the intercostal muscles. The likelihood of paralytic polio and the extent of paralysis increases with the age of the patient. In children, paralysis is only seen in 1 in 1000 cases with paralysis of 1 leg being most common. But in adults, this rises to 1 in 75 cases with an increased chance of paralysis of the chest, abdomen, and all four limbs. If affected nerve cells in the spinal chord are completely destroyed paralysis will be permanent, but cells that are not destroyed but lose function temporarily may recover within 4 to 6 weeks, and approximately 50% of patients will recover fully, and 25% will be left with only minor disability. The most severe disease is seen where the virus destroys neurons in the bulbar region of the lower brain. This occurs in only about 2% of cases of paralysis, and leads to weakening of the muscles supplied by the cranial nerves, producing symptoms of encephalitis, and causing difficulty in breathing, speaking and swallowing. Without respiratory support, respiratory poliomyelitis can lead to suffocation or pneumonia from aspiration of secretions and 5–10% of patients with paralysis will die due to paralysis of the muscles used for breathing – 2–5% of children and up to 15–30% of adults.

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The story of the eradication of polio begins with Franklin D Roosevelt who contracted the disease in 1921 at the age of 39. In 1927, he founded the Georgia Warm Springs Foundation, a hydrotherapy centre for the treatment of victims, and throughout his Presidency of the United States continued to raise funds, initially for the alleviation of the debilitating effects of the disease, but after 1938 with the creation of March of Dimes, for research into its eradication. This was widely supported by celebrities from the entertainment world including Eddie Cantor and Elvis Presley. The March of Dimes made its first research grant in 1938 to Yale University and by 1955 had invested $25,500,000 in research, culminating in the development of vaccines without which eradication would not have been possible.

The first attempt to produce a vaccine was in 1936 when Maurice Brodie, a research assistant at New York University, used ground-up spinal chord from infected monkeys. The resulting vaccine was tried out on Brodie and his assistants and on 3,000 children, many of whom developed allergic reactions. None developed immunity. The breakthrough came in the late 1940s and early 1950’s when it was shown that it was possible to grow the virus to high titres in cells derived from human and monkey tissues grown in cell culture in flasks.

The two great pioneers of polio vaccine were Jonas Salk and Albert Sabin. Salk was first to produce and license a successful vaccine. This was an inactivated vaccine prepared from the three types of the virus grown in monkey kidney cell culture and inactivated with formalin. It was licensed in 1955 and immediately children's vaccination campaigns were launched in developed countries. In the US, following a mass immunisation campaign promoted by the March of Dimes the annual number of polio cases fell to 5,600 by 1957, and by 1961 only 161 cases were recorded in the US. The inactivated vaccine induced an excellent immune response that successfully prevented infection of the central nervous system. However, it did not prevent infection of the gastrointestinal mucosa, which meant that the virus could still circulate in the population, and cause paralysis in unvaccinated people. It was realised that successful eradication of the virus would depend on the development of a live attenuated vaccine that could be given my mouth rather than injection. This was achieved by serial passage of the virus in non-human cells at sub-physiological temperatures, resulting in spontaneous mutations of the viral genome and loss of pathogenicity, though not of the ability of the virus to replicate in the human gut. Unfortunately, this attenuated vaccine can regain its pathogenicity after it has been transmitted from person to person a sufficient number of times. To prevent this causing outbreaks of paralytic disease it is essential to ensure that a sufficient proportion of the population are successfully vaccinated, the so-called effect of herd immunity which makes it improbable that non-immune individuals will come into contact with the virus. The first successful live attenuated vaccine was produced by Albert Sabin and after it was licensed in the early 1960s, a second wave of mass immunisation led to a further dramatic decline in the number of cases. Between 1962 and 1965 about 100 million Americans received the Sabin vaccine.

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In the developing world, where organized health care was still in its infancy, the picture was different, however, and by 1988 there were still 125 countries with endemic polio and more than 350,000 cases of paralytic disease annually. It was realised that world-wide eradication of the disease would only be achieved by mass vaccination campaigns funded by the richer countries of the world.

Rotary International first became involved with polio when it committed to providing oral polio vaccine for 6 million children in the Philippines. Spurred by the success of this campaign, Rotary worked with Sabin on a plan to immunise all children against polio, giving rise to Rotary’s PolioPlus programme in 1985. In October of that year on the fortieth anniversary of the foundation of the United Nations, Rotary pledged $120 million to this programme which among other things, funded the formation of a core group of experts at the World Health Organisation to oversee the campaign. In 1988 the World Health Assembly, as a result of the encouragement and financial pledge of Rotary International, unanimously declared to a goal of eradication polio from the world by the year 2000. Although, this has proved to be an over-optimistic target, the efforts of the four spearheading partners of the campaign ­­– WHO, Rotary International, Unicef and CDC Atlanta – with financial support from many governments, and since 2007 by the Gates Foundation which promised to match donations made by individual Rotarians and Rotary Clubs, initially dollar for dollar, but in recent years at 2 dollars for every dollar, it is now confidently believed that the wild-type poliovirus will be eradicated by 2018. To date, in this current calendar year, there have been only 27 cases paralytic disease caused by wild-type poliovirus. This amazing success story has been achieved not only through the persistence of Rotarians, who have donated several hundred million dollars since 1985, but perhaps more importantly, given billions of hours of volunteer time, particularly in the polio-endemic countries of Africa and the Indian sub-continent, in organising and running mass immunisation days, often in the face of great difficulties, among them armed conflict in areas where polio is still endemic.

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Even after the last recorded case of wild-type poliovirus disease, the campaign will need to continue for many years. Once there have been no recorded cases of the disease in any country, the oral vaccine will be replaced by the inactivated vaccine, which will have to remain part of the childhood vaccination protocol for many years. But even more important will be the role of surveillance and examination of all cases of acute flaccid paralysis, which may be caused by several closely related viruses, and monitoring of the environment. This will continue to be very costly, and the cost is estimated to be between $200 million and $250 million annually.

The final point that needs to be made is that if the campaign were to stop before eradication is fully assured, it is estimated that there would be 200 million cases of paralytic polio annually within only a very few years. Success is in our grasp, but it requires continued dedication and the donation of millions of dollars annually to ensure that this terrible disease never returns to plague mankind.