It is not yet clear how virologist Sheik Umar Khan caught the virus. Photo: Reuters

The head doctor fighting an outbreak of the deadly Ebola virus in Sierra Leone has himself caught the disease, one of a growing list of medical workers infected while battling to halt its spread across West Africa.

Ebola has killed 632 people across Guinea, Liberia and Sierra Leone since an outbreak began in February, putting strain on a string of weak health systems facing one of the world’s deadliest diseases despite waves of international help.

A statement from the president’s office said 39-year-old Sheik Umar Khan, a Sierra Leonean virologist credited with treating more than 100 Ebola victims, had been transferred to a treatment ward run by medical charity Medecins Sans Frontieres.

A source at the ward confirmed that the doctor was alive and receiving treatment, but gave no details of his condition.

Khan has been hailed a ‘national hero’ by the Health Ministry for his efforts to lead the fight against an outbreak that has killed 206 people in the West African nation.

Khan has been hailed as a ‘national hero’ for his efforts to lead the fight against the outbreak

There is no cure or vaccine for Ebola, which can kill up to 90 per cent of those infected, although the mortality rate of the current outbreak is around 60 per cent.

It was not immediately clear how Khan had caught the virus. His colleagues said he was always meticulous with protection, wearing overalls, mask, gloves and special footwear.

Three days ago, three nurses working in the same Ebola treatment centre alongside Khan died from the disease.

Tarik Jasarevic, a spokesman for the World Health Organisation, said around 100 health workers had been infected by Ebola in the three countries, with 50 of them dying.