Robert Parsons reports

In Russia's overcrowded prison system a deadly disease is on the march. Many of these prisoners have a new untreatable form of tuberculosis (TB) and it is spreading with terrifying speed.

Ten per cent of Russia's one million prisoners suffer from TB and 20% of them are thought to have the drug-resistant strain - which means 20,000 people are condemned to die.

Prison clinics do not have the funds for effective treatment

The disease is multiplying in the festering conditions of Russia's overcrowded cells.

In many prisons inmates have to sleep in shift. Poor diet, stress and depressed immune systems make the prisoners vulnerable targets. TB does not distinguish between the gravity of the crime committed.

One prisoner tells his story: "I lost my freedom for stealing three sacks of barley and now I'm ill with tuberculosis. Maybe I will get better, maybe I won't - but I doubt I'll get better in here."

Time bomb

Prison clinics cannot afford to treat patients with the full course of drugs, so the disease becomes resistant and even more difficult and expensive to cure.

Overcrowding provides a fertile breeding ground for disease

Russia's penal system is becoming a time bomb for the rest of the world. Once TB-infected prisoners step outside the prison gates, there is nothing to stop them spreading the disease onto the streets of Russian cities and beyond.

Most of the people standing outside a European charity run clinic in Moscow are ex-prisoners. Many of them have TB and all are homeless.

Because they are not registered with the city authorities, the Russian health system refuses to treat them.

Ancient menace

Tine Demeulenaere of the charity Medecins sans Frontiers says: "From prisons, inmates catch TB. They are not cured or only half-cured and when they are released they go out onto the streets.

"They infect other people, their wife and children and these people also become ill and in turn infect others who might travel and in this way it can be all over the world before you know it."

The clinic is one of the few places in Russia where ex-prisoners can go for treatment but it barely scratches the surface of the problem - drug resistant TB is well beyond its resources.