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 British man, William Pooley, is being treated for the Ebola virus 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.
But health experts say it's extremely unlikely Ebola could spread here because UK healthcare is much more advanced.
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 in Liberia, told Newsround what it's like to work in such a difficult environment.
She said it was exhausting and frightening, but also very rewarding to see patients recover.