By Georgina Kenyon

Health experts have uncovered a case of a European man who is carrying the polio virus but has not developed the disease - even though his immune system is weak.

Doctors cannot explain why the man is not seriously ill and wonder if the polio virus could be changing.

We are putting diseases and viruses under pressure like we have never done before by such an enormous amount of international travel

Professor John Oxford

They say the case proves that there is no room for complacency over the continuing need for vaccination programmes - even though the disease has officially been eradicated in Europe.

Doctors stress the man they now call "Polio Man" is not a serious health hazard.

However, he is key to understanding how to deal with what virologists term "the end game" of polio vaccination programmes - when polio vaccination programmes can be ended safely.

No paralysis

"Polio Man" is immunodeficient but doctors are extremely surprised that he has not developed paralysis or any form of the disease.

Vaccination has been a great success

Paralysis usually occurs in just one in 100 cases of polio infection but it nearly always occurs when the person has a weakened immune system.

"Polio Man" shows that the polio virus may be changing and is no longer following the usual path of infection.

If so, doctors are wondering if current vaccines are adequate to control the disease.

The case shows that even though the disease appears to be beaten, it could still be lurking undetected and ready to strike.

Further infections

Dr Philip Minor, head of virology at the UK National Institute for Biological Standards and Control, thinks that the weakened form of the virus that "Polio Man" originally received in the oral vaccine has somehow mutated inside his body back into the full-strength natural virus.

He said: "Although there is no official record that anyone has caught polio from him, it is a possibility.

"We find this a very interesting case. Unvaccinated children could be at risk of contracting polio if their mothers have not passed on antibodies onto their children.

"The man is not likely to be in contact with small children.

"But this is why vaccination programmes are important. People who are vaccinated are not at risk."

The World Health Organization (WHO) officially stated on 21 June that polio had been eradicated in Europe, following its eradication earlier in the Americas and Western Pacific.

The disease is said to be eradicated when no cases are recorded for three years.

However, health experts are debating how polio can remain eradicated worldwide and when vaccination programmes can stop altogether.

Gastric problems

"Polio man" is in his late 20s, has never suffered from polio and was vaccinated against the disease.

He is suffering from chronic immunodeficiency and chronic gut problems such as diarrhoea which is common in such patients.

Doctors were alerted to his case in 1995 when conducting a study into gastric problems associated with immunodeficiency.

One test during the study involved analysis of the man's faeces and this revealed the presence of polio.

It appears he may have been excreting the live virus in his faeces for over 20 years

The case is also very relevant in light of the continuing MMR debate and how necessary vaccination programmes are to protect worldwide populations from the disease.

John Oxford, Professor of Virology, St Bartholomew's and the Royal London School of Medicine, London, UK, said: "Until the scientific community sorts out infectious diseases and learns how to control them, we cannot start thinking about more complicated advances in health.

"We are putting diseases and viruses under pressure like we have never done before by such an enormous amount of international travel. These diseases want to survive.

"No vaccine is safe, but it's a damn sight better than the real disease," he said.

Professor Oxford also explained that recombinant diseases may become more of a problem where diseases join to form a new disease combination by swapping genes.

Dr Minor and his colleagues are currently writing a scientific paper on the man, set for publication in a medical journal later this year.