America's top infectious diseases official says he thinks we can get to "zero cases" of Ebola in West Africa.

In our interview today, Dr Tom Frieden was keen to stress to me that he was optimistic, not confident, that this could be achieved - saying on a recent trip to the region he saw a lot of improvement.

What worries him is complacency now that progress is being made in Sierra Leone and Liberia. Guinea, he says, still has a long way to go.

On grading how the world has handled Ebola, Dr Frieden would only say that no one would pretend mistakes had not been made.