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HISTORY OF POLIOMYELITIS

Poliomyelitis is said to have first occurred nearly 6,000 years ago in the time of the Ancient Egyptians. The evidence for this, is in the withered and deformed limbs of certain Egyptian mummies. The following are the more important dates in the history of polio:

ANCIENT EGYPT 3.,700 B.C. - An Egyptian mummy with probable polio. If this was polio, cases almost certainly occurred before then.

1,580 - 1,350 B.C. — The Priest Ruma with a withered leg and equinus foot - shown on a plaque and probably poliomyelitis.

1,209 B.C. — Mummy Giptah with an equinus foot.

MIDDLE AGES 1559 — Painting by Pieter Bruegel showing a crippled beggar. Not necessarily polio although it probably did occur during this period in England.

EIGHTEENTH CENTURY 1789 — First known description of poliomyelitis by Underwood.

NINETEENTH CENTURY 1834 — First epidemic of poliomyelitis in the island of St. Helena.

1855 — First description by Duchenne of the pathological process in poliomyelitis with the involvement of the anterior horn cells of the spinal cord.

TWENTIETH CENTURY 1908 — Transmission of poliomyelitis to a monkey by Landsteiner. 1909 — Passage of the virus through a monkey by Flexner.

1949 — Growth of the virus on tissue culture.

1951 — Three types of polio virus isolated and identified.

1954 — First large scale trial of Salk (dead vaccine) by injection.

1958 — First general use of Sabin (live attenuated vaccine) by mouth.

Polio through the Ages

POLIOMYELITIS IMMUNISATION

Governments with poliomyelitis problems (in developing countries) hesitate to venture on an enterprise soon to collapse because of lack of funds, personnel, communications and transport. Live poliomyelitis vaccine is unstable without refrigeration-, while the more stable Salk vaccine is so expensive that few can afford even a single dose. Perabo, 1970

The main defence against poliomyelitis is prophylactic immunization, as public health measures only play a very small and subsidiary role in prevention. This situation is unlikely to improve, as the exact mode of infection is still incompletely understood. World-wide immunisation campaigns are, therefore, essential both to diminish and eventually eradicate polio. At present, with the exception of some islands, only the developed countries of the world have been adequately immunised, but even these countries may not continue to be protected due to increasing public apathy to vaccination.

It is also likely that hundreds of thousands of new cases of poliomyelitis now occur every year,, mainly in the populations of the developing tropical and subtropical countries of the world and the risk of spread to Europe and North America in the future is considerable, if vaccination is not continued energetically. The problem is greatly underestimated by economically rich countries, as probably less than 1 in 100 patients with poliomyelitis in developing countries are even notified. The figures provided to the World Health Organisation can only show a tiny fraction of the total number of cases.

TYPES OF POLIO VACCINE

There are two main types of vaccine, a killed vaccine given by injection (Salk) and a live attenuated vaccine given by mouth (Sabin). It has now been shown that the live attenuated vaccine is not only much cheaper, but has many other advantages over the dead vaccine. In addition, by modern methods of manufacture, it is extremely safe, and the chances of causing paralysis are less than one in a million.

It is also becoming apparent in developing countries that as the infant mortality falls below 80 per thousand, due to a general improvement in health and hygiene, paradoxically the likelihood of epidemics of polio recurring increases. This is because the polio virus is normally endemic in most of these countries, and therefore most children are infected with the virus during infancy when they are still protected with a high circulating level of maternal antibodies. They therefore acquire immunity to the disease without becoming paralysed as the maternal antibodies give them adequate protection against paralysis.

As the health and hygiene of a community improves, however, the children are less likely to get subclinical infections as infants, and may become infected instead for the first time at the age of 1 or 2 years or even much later when they have lost their maternal antibodies and protection. They will therefore be susceptible to paralytic poliomyelitis, and epidemics will become more frequent. In communities with an even higher degree of hygiene the age of acquiring the disease and immunity become later and later until at the present date in Europe and North America only one-third of all new polio cases are under the age of five. No less than one-third are over 15 and one-third between the ages of 5 and 15. This lack of immunity makes it essential that people from these countries be immunized before travelling to parts of the world where poliomyelitis is endemic or epidemic. It must also be remembered that, while early immunity appears to occur in urban communities in countries with a poor hygienic standard, the same is not necessarily true for isolated rural communities.

It has been shown, for instance, that while over 90% of the cases of polio occurring in urban populations in Uganda occur in those under five years of age, in some rural communities in Uganda only one-third of those under 5 have any immunity at all. Thus it may be seen that it is essential for immunization campaigns to be carried out as a matter of urgency in all developing countries.