Consigning poliomyelitis to history

Much publicity was given recently to the announcement by Microsoft founder Bill Gates that he is prepared to donate $10bn of his own money in an effort to eradicate poliomyelitis within the next five years.

The disease is a viral infection, and has caused paralysis and death for much of human history. The oldest identifiable reference is an Egyptian stone engraving from 1000BC.

Approximately 95 per cent of polio cases are asymptomatic, with most of the rest causing minor, flu-like symptoms. However, up to 0.5 per cent of cases affect the central nervous system, producing symptoms of paralysis of varying severity, including of one or more limbs, and of the respiratory muscles, depending upon which nerves are affected.

The virus is carried in the saliva and faeces of the host, and is spread either by direct contact or by droplet infection. Reported cases of poliomyelitis have dropped from over 350,000 in 1988 to 1,604 in 2009, a direct result of global efforts at eradicating the disease, which remains endemic only in Northern India, Pakistan, Afghanistan and Nigeria.

In the 1960s two vaccines were developed, one using inactivated virus, which was injected into patients, the other using an anattenuated strain, which was able to be administered orally, replicating in the gut, but unable to access the nervous system.

These vaccines resulted in the rapid eradication of polio in the industrialised world. The economic effect has been huge, and it was suggested that the cost of the vaccine development programme paid for itself every three weeks.

It is with this in mind that the World Health Organization has teamed up with Mr Gates in a determined effort to consign polio to history by the year 2015, something achieved for smallpox over 30 years ago. A dose of vaccine costing 50p can protect a child against polio for life.