Nearly 400 people have died in the outbreak which started in Guinea and has spread to neighbouring Sierra Leone and Liberia.

It is the largest outbreak in terms of cases, deaths and geographical spread.

The WHO said it was “gravely concerned” and there was potential for “further international spread”.

The outbreak started four months ago and is continuing to spread.

So far there have been more than 600 cases and around 60% of those infected with the virus have died.

Ebola, a haemorrhagic fever, has no cure and is spread by contact with the fluids of infected people or animals, such as urine, sweat and blood.

Most of the deaths have been centred in the southern Guekedou region of Guinea.