The World Health Organisation declared Australia polio free in 2000. But the disease remains a threat in Africa, Afghanistan and Pakistan, which recorded its highest level of polio infections in a decade last year.

And in Australia, the disease is still very much with us.

It is estimated there are 400,000 Australian polio survivors. Peak body Polio Australia says this makes them the single-largest physical disability group in the country.

From the 1930s to the 1960s, at times polio reached epidemic proportions in Australia. The virus attacks the motor neurons that relay messages from the spinal cord to muscles and can lead to muscular degeneration and, in some cases, paralysis.

Widespread use of the polio vaccine eventually halted its spread. But for thousands of polio survivors, the disease is not finished. Decades after they contracted polio, symptoms can return in the form of post-polio syndrome (PPS).

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Frances Henke contracted polio in 1946, when she was just two years old. More than 40 years later, she began to experience severe fatigue. And her left leg, which had been badly damaged by polio, was becoming more and more sensitive to temperature swings.

"It's all in your head, you know," she said doctors told her at first.

"And then I found an article ... and it talked about post-polio syndrome. And I thought, 'at last'."

Frances Henke contracted polio when she was two years old, and now works with Polio Network Victoria to help raise awareness of post-polio syndrome. ( ABC News )

Ms Henke now works with Polio Network Victoria to help spread awareness of PPS. One of the biggest challenges she faces is that many polio survivors may not even know they contracted the disease as infants.

"There's so many who were told 'the state doesn't want a bunch cripples, never admit that you had polio'," Ms Henke said.

"Many parents were ashamed."

Other polio survivors simply are not aware symptoms can return decades after they have recovered from the disease and moved on with their lives.

Kenneth Toohey, 82, contracted polio in 1938. Like many other children, he spent time in an iron lung — a massive device that helped polio victims breathe.

"I hadn't even ever thought it would come back in later years. Never entered my head," Mr Toohey said.

"I can remember ... 30 or 40 iron lungs in a row, and all of us talking to each other through the mirrors."

For two decades he has been dealing with the effects of PPS on his right leg, which was badly withered by polio.

Kenneth Toohey, 82, contracted polio as a child in 1938, and has been dealing with post-polio syndrome for two decades. ( ABC News )

"Since about 58 [years old], I started to notice things were different. The leg was getting shorter," he said.

"Now [it's] what's commonly called a club foot. It rose five centimetres."

Doctors say because polio has been off the radar for so long — for both patients and the medical profession — PPS is often misdiagnosed.

Senior rehabilitation physician Stephen De Graaf is perhaps Australia's best-known PPS specialist.

"Throughout society it tends to be missed," Dr De Graaf said.

"It gets put away as arthritis, or 'you're just getting old'. But it's more than just getting old. It often means that they're becoming more physically inefficient."

Post-polio syndrome takes high emotional toll: specialist

There are relatively young people also living with PPS, like Nga Nguyen, who contracted polio as a child in Vietnam.

From the age of two until she was 18, Ms Ngyuen was in a rehabilitation hospital.

Nga Nguyen was in a rehabilitation hospital for 16 years from the age of two, after contracting polio as a child in Vietnam. ( ABC News )

She eventually joined her family in Australia in 2010. PPS has led to worsening pain in her backbone, and she is worried for the future.

"Now I can sit in the wheelchair, I don't know after a few years — could I sit?" Ms Nguyen said.

"I'm scared."

Advocates say they not only want to see more awareness of PPS, they also want those diagnosed to know what they are in for — and to reach out for help.

Dr Stephen De Graaf says PPS takes an especially high emotional toll, because polio survivors spend decades overcoming the effects of the disease to lead productive lives.

When PPS hits, there is nothing they can do.

"We're in a situation where we're not going to be able to cure what happens," Dr De Graaf said.

"We have to manage it."