Poliomyelitis, a viral infectious disease, had once paralyzed and crippled hundreds of thousands of children each year. But the development of vaccines and a global effort to eradicate the disease dramatically reduced the number of infections.

However, the World Health Organisation says the success-story is at risk and the UN agency is expected to declare polio a global health emergency on Friday.

The WHO says that a drastic rise in infections in Nigeria, Pakistan and Afghanistan, poses a threat to the rest of the world.

Tarek Bazley reports.