The deadly virus Ebola has killed more than 1,500 people in the latest outbreak of the disease in West Africa.
In the fight to try to stop the disease spreading, doctors and medical staff from the UK and other countries are helping to treat those infected in Sierra Leone, Liberia, Guinea and Nigeria.
A back here in the UK after catching it working in Sierra Leone.
Doctors wanted to make sure he's given the best treatment possible which is why he was flown back to London.
So why do so many doctors, nurses and medical staff risk their lives in dangerous places?
Dr Nathalie MacDermott, who's worked with Ebola sufferers, told Newsround what it's like to work in such a difficult environment.