More About Polio

Poliomyelitis, generally known simply as polio, is a paralytic disease caused by poliovirus. The poliovirus has three strains, so it is possible to contract the disease more than once.

Polio is spread through human-to-human contact, with the virus entering the body through the mouth and infecting the small intestine. Although it can affect people of any age, it strikes children more often than adults.

The initial symptoms of polio infection are flu-like, typically including fever, headaches, tiredness and muscle stiffness. Most cases of polio do not proceed past this non-paralytic stage and can be so mild that it is possible not to be aware one has the disease.

In a small minority of cases, the virus spreads and infects the central nervous system, specifically motor neurons in the spine. As the motor neurons are attacked, the muscles in the limbs feel tight and become unresponsive, a type of paralysis called acute floppy paralysis. The legs are most often affected, but in particularly severe cases the torso can also be paralysed, possibly leaving the victim needing an iron lung to breathe.

The disease may spread beyond the spine and infect the brain stem, in very rare cases, in which case it is known as bulbar polio. The cranial nerves in the brain stem control a wide range of functions in the body, including facial muscles and nerves, eyeball muscles, vision, smell, hearing, swallowing and heart, lung and intestinal functions, as well as others. Bulbar polio can affect any of these functions and is quite often fatal.

The damage to the nerves in paralytic polio is irreversible, though it is possible to recover from paralysis, at least partially, through sprouting from neighbouring neurons. As well as lingering paralysis, other long-term effects of polio can include withered limbs, hunched backs and respiratory problems. Additionally, many polio sufferers also suffer from post-polio syndrome.

Since polio is transmitted from person to person, occurrences of polio have increased as human populations have increased. Additionally, improvements in sanitation may also have reduced people’s immunity. In the first half of the 20th century, the Western world experienced increasingly acute epidemics, which caused widespread fear in the population.

After much effort a vaccine for polio was developed in 1955 and intensive immunisation campaigns worldwide have successfully eradicated the disease from much of the world. Immunisation in New Zealand began in 1957 and the last reported case due to wild poliovirus was in 1962. There have been nine vaccine-related cases since 1962. However, in 2002, immunisation was switched to the inactivated polio vaccine, which is not associated with vaccine related infections.