24 October is World Polio Day, an event that aims to raise awareness of the continuing threat of polio to children in some parts of the world. A global effort to eradicate the disease has been ongoing for 26 years, reducing the number of cases from over 350,000 in 1988 to 406 in 2013. Today, only three countries – Afghanistan, Pakistan and Nigeria – have yet to eradicate the virus. However, in 2014, new cases of polio have also been documented in Iraq, Syria, Cameroon, Equatorial Guinea, Somalia and Ethiopia – all countries that were previously polio-free. This reintroduction of the disease highlights that as long as a single person remains infected, polio can return. According to the World Health Organization, a renewed spread of polio could cause up to 200,000 new cases over the course of a decade and cost the global economy billions of dollars.
What is polio?
Polio is short for Poliomyelitis and is also known as infantile paralysis. It is an infectious disease caused by the three different types of poliovirus, which mainly infect children under 5 years of age. Polioviruses can live in an infected person’s faeces for several weeks and are transmitted mainly via the faecal-oral route, meaning that they can spread through water supplies and food in unsanitary conditions. Polio can also be spread through droplets from the sneezes and coughs of infected people.
Polioviruses first enter the body through the mouth, infecting the oral cavity and the digestive system. Polio can be completely asymptomatic, but if the virus spreads into the bloodstream and the central nervous system, paralysis can manifest itself in three different forms:
- Spinal polio is the most common form of paralytic polio, causing paralysis of limbs within just a few days. The likelihood of developing paralysis, as well as its extent, increase with age: children usually suffer paralysis of one or both legs while adults are at higher risk of full quadriplegia.
- Bulbar polio occurs if polioviruses infect the brain stem. Its symptoms include difficulty speaking, breathing and swallowing, and it can lead to acute encephalitis (inflammation of the brain). The infamous iron lung, which helps patients breathe, was widely used before vaccinations and technological innovations rendered this imposing machine obsolete.
- Bulbospinal polio is a relatively rare combination of the above two types. Infection of the diaphragm and the nerve that drives it means that patients are left unable to breathe without assistance.
How can we eradicate polio?
There is no known cure for polio. However, several vaccines exist – the most widespread one of these is the oral polio vaccination (OPV), which is cheap, easy to administer and provides effective protection against the virus. In extremely rare cases (1 in 750,000) the attenuated virus in the vaccine can revert into a form that can cause paralysis, so some countries choose not to use it. Instead, they utilise the inactivated polio vaccine (IPV), which is administered via injections and was the first polio vaccine to be developed.
Polioviruses only infect humans and cannot survive for long in the environment outside a host. The disease can therefore be considered well and truly eradicated when every person at risk is vaccinated – but until then, even a single case has the potential to develop into a large outbreak.
What is left to do?
Polio remains endemic in just three countries (Pakistan, Afghanistan and Nigeria), meaning that the virus occurs in the wild here. The few cases reported elsewhere are generally imported from the three endemic countries. Of the three strains of poliovirus, one has been completely eradicated.
India was considered the most difficult country to eliminate polio in due to its size, population and infrastructural challenges – but in January 2011, this important milestone was achieved. As a result of the successful worldwide vaccination campaign, 80% of the global population now live in countries that are polio-free and the number of polio cases has fallen by over 99% since 1988.
However, vaccination programmes are not without their difficulties. Over the past few years, scores of front-line vaccination workers have been murdered in Pakistan, Afghanistan and Nigeria. Many blame religious fundamentalist groups for the violence, and a number of these groups openly oppose vaccination campaigns.
Religious leaders are now being engaged to educate the population on the dangers of polio and the benefits of the vaccine. We can only hope that the world will be polio-free in the near future, preventing the suffering of many children.