The death toll from the worst Ebola outbreak in history has jumped by almost 200 in a single day to at least 2,296 and is already likely to be higher than that, the World Health Organisation said yesterday.

The WHO said it had recorded 4,293 cases in five West African countries as of September 6, a day after its previous update. But it still did not have new figures for Liberia, the worst-affected country, suggesting the true toll is already much higher.

The WHO has said it expects thousands of new cases in Liberia in the next three weeks.

As well as struggling to contain the disease, the organisation is having difficulty compiling data on the number of cases, said Sylvie Briand, the director of WHO’s department of pandemic and epidemic diseases.

“We know that the numbers are under-estimated. We are currently working to estimate the under-estimation,” Briand told a news briefing in Geneva.

“It’s a war against this virus. It’s a very difficult war. What we try now is to win some battles at least in some places.”

The outbreak began last December and has been gathering pace for months, but about 60 per cent of Liberia’s cases and deaths occurred within the last three weeks, the data showed.

In Guinea and Sierra Leone, the other two countries at the centre of the outbreak, only 39 per cent of cases and around 29 per cent of deaths have occurred in the last three weeks, suggesting they are doing better at tackling the outbreak.

The new figures also showed two new suspected cases in Senegal in addition to one previously confirmed case there, but a fall in the overall number of cases in Nigeria from 22 to 21, as at least one suspected case turned out not be Ebola.