Telling Science

What is polio?

Polio – or poliomyelitis – is a viral disease that causes muscle paralysis, especially in children.

An Egyptian stele thought to represent a polio victim. <br> 18th Dynasty (1403–1365 BC).

An ancient disabling disease

Egyptians recorded the existence and impact of polio (poliomyelitis) in their hieroglyphs over 2000 years ago. Today, polio has almost completely disappeared as a transmissible disease, thanks to the impact of successful vaccines developed last century. Also known as ‘infantile paralysis’, polio is a viral disease caused by the consumption of water or food contaminated with polio-infected faeces. While most people show few or no symptoms, for some – particularly children without immunity – polio can cause severe disability.

Polio terrified every parent in the early 20th century. The virus can cause spinal and respiratory paralysis and if the polio virus affects the lung muscles or brain it can be fatal. Children are particularly vulnerable – hence the name “infantile paralysis”. Polio once disabled more than half a million people of all ages around the globe every year. New Zealand experienced a series of epidemics from 1946 to 1962 when the last case was notified to the Ministry of Health.

The exterior of a type 3 poliovirus protein shell. Manuel Almagro Rivas, CC BY-SA 4.0, via Wikimedia Commons.

Better hygiene hinders immunity

Most babies got immunity from their mother’s milk, and when exposed to the polio virus early enough, developed long-term immunity. Ironically better hygiene and sanitation at the end of the 1800s stopped that early exposure.

While many people with polio show no or few symptoms, in a very small percentage, the polio virus reaches the spine from the central nervous system and destroys the motor neurons that stimulate muscles to contract. This causes muscle weakness, and even paralysis. There is no cure, but vaccines can prevent the disease altogether.

This iron lung is on display at Whanganui Regional Museum. Iron lungs like this one were used in specialist polio hospitals around New Zealand.

Is there a cure for polio?

While there is no cure for polio, a vaccine developed in the 1950s has seen the incidence of polio almost eradicated worldwide. New Zealand hasn’t had a case of polio since 1977 but many older kiwis are still affected by polio today, having caught the virus when they were young.

There are two vaccines used to protect against polio disease. One is an inactivated poliovirus (known as IPV) which is given by injection, and the other is a weakened poliovirus given by mouth (OPV). New Zealand switched from the oral vaccine to the injected IPV vaccine in 2002.

Today, a form of polio derived from the vaccine has been detected in waste-water overseas, suggesting that the disease is circulating once more, reinforcing the need for a global focus on polio vaccination.