David Cameron is to take part in a video conference call on Wednesday afternoon with Barack Obama and EU leaders to discuss the growing Ebola crisis amid warnings that the outbreak could grow to 10,000 new cases a week within two months.

As the death toll from the virus reached 4,447 people, nearly all of them in west Africa, Downing Street confirmed that the prime minister would join a conference call with Obama and the leaders of France, Germany and Italy.

It is understood that the leaders will discuss what further action can be taken to help stop the spread of the virus in west Africa.

They will also discuss the steps that are being taken to screen air passengers arriving in Europe and the EU from west Africa.

The news of the conference call came after Dr Bruce Aylward, assistant director-general of the World Health Organisation (WHO), told a news conference in Geneva that the number of new cases was likely to be between 5,000 and 10,000 a week by early December.

Aylward told a news conference in Geneva on Tuesday that the number of new cases was likely to be between 5,000 and 10,000 a week by early December.

WHO’s regular updates show that deaths have resulted from 4,447 of the 8,914 reported cases, but Aylward said that any assumption that the death rate was 50% would be wrong. He put the death rate at 70% because many deaths are not reported or recorded officially.

Where detailed investigations have been carried out, it was clear that only 30% of people were surviving, he said, adding that the figure was almost exactly the same in the three hardest hit countries, Guinea, Liberia and Sierra Leone. “This is a high-mortality disease in any circumstances but particularly in these places,” said Aylward, adding that it was not the WHO’s job to judge how different countries responded to the Ebola outbreak.

The grim forecast came as the first returning passengers from west Africa to Heathrow airport were asked to undergo temperature checks and questionnaires about their contacts with Ebola patients. The £9m screening exercise has been criticised by some experts, who say it will not pick up those who have the virus but are not yet symptomatic.

In the US, it emerged that a nurse who contracted Ebola has been given a blood transfusion from Dr Kent Brantly, who has recovered from the disease. The nurse, Nina Pham, was infected while caring for Thomas Duncan, who was taken ill on a visit from Liberia and died in Texas Health Presbyterian hospital, Dallas.

Brantly has donated blood for three Ebola patients, including Pham. “He’s a doctor. That’s what he’s there to do. That’s his heart,” said Jeremy Blume, a spokesman for the non-profit medical mission group Samaritan’s Purse, which Brantly was working for in Liberia. The WHO said plasma from people who had overcome Ebola, which contains antibodies against the virus, should be tried as a treatment, but it is hard to use outside the sophisticated healthcare settings of the west.

The US president said on Tuesday night that the “world is not doing enough” to combat the disease, and that “everybody’s going to have to do more than they are doing right now”. Obama said he wants to make sure lessons learned from Pham’s case are applied to health centres around the US.

The UN Mission for Ebola Emergency Response, newly set up to coordinate the fight against the disease, has set targets to isolate 70% of suspected cases in west Africa and safely bury 70% of the dead within the next 60 days – described as the 70-70-60 plan.

It is a tough target, said Aylward, but if it takes 90 days rather than 60, “a lot more people will die who shouldn’t and we will need that much more capacity on the ground to manage the caseload”.

As the numbers continue to rise, the need for beds and health personnel to treat the sick will increase – and there is a serious shortage of trained and experienced people to lead the effort, according to Aylward.

Good training programmes are being put in place, particularly by the UK and the US, “but there is still the challenge of getting internationals on the ground who have expertise – in Ebola ideally”.

For the past four weeks, about 1,000 new infections a week – including suspected, confirmed and probable cases – have come to light. Aylward said the WHO was concerned about the continued spread, especially in the capital cities of Sierra Leone, Guinea and Liberia – Freetown, Conakry and Monrovia.

“The virus is still moving geographically and escalating in the capitals,” he said. Large treatment centres are taking a long time to build and staff and those that exist are full. A new strategy, which the UK is supporting in Sierra Leone, is to set up a lot of community care units with a handful of beds, where people can stay and get basic care rather than endangering their families at home, while waiting for a treatment centre bed.

The units will also help people arriving with fever because they have malaria. At the moment, they are not being treated or are afraid to go to hospital.