The Ebola death toll in the Democratic Republic of Congo has reached 319, official figures have revealed.
Health chiefs fear 542 people in the African nation have been struck down in the second biggest outbreak of the virus in history.
The World Health Organization (WHO) said efforts to contain the outbreak, which began in August, have been challenging.
Aid workers have found it difficult to provide help in the worst affected regions of the DRC because of ongoing armed conflict.
The death toll of Ebola has reached a suspected 319, including 271 confirmed, in the Democratic Republic of Congo during the second biggest outbreak in history
It comes as neighbouring countries remain on high alert amid fears the killer virus – responsible for a brutal epidemic in 2014 – could spread.
The confirmed figures show 491 people have been struck down with Ebola – with a further 51 currently undergoing testing.
The WHO data also revealed the confirmed death toll is 271, as the remaining 48 deaths continue to be thoroughly investigated.
Experts warn the infection is being spread because people are moving in and out of the region, while some communities are not engaging.
Provinces North Kivu, which includes the heavily populated cities of Beni, Kalunguta and Mabalako, and Ituri remain the centre of the outbreak.
Some areas, which had previously recovered, have seen a reintroduction of cases, such as Musienene – where the last reported case was 32 days ago.
International groups are finding it difficult to provide aid during armed conflict in the region. Pictured, a member of the medical staff western Uganda, December 12
The public health agency estimates that more than a million refugees and internally displaced people are traveling through and out of North Kivu and Ituri, contributing to the rapid spread. Pictured, a medical assistant uses a non-contact thermometer to check the temperature of people at the border between the Congo and Uganda, December 12
North Kivu and Ituri remain the centre of the outbreak. Pictured, a health worker feeds a boy suspected of having the Ebola virus, September 9
Health experts have said this Ebola outbreak, the tenth to strike Congo since the virus was discovered there in 1976, is like no other.
Aid workers face the threat of attack from armed groups and resistance from a wary population in a region that had never faced an Ebola outbreak before.
Armed rebels have attacked, kidnapped and killed medical staff trying to combat the outbreak and equipment has been destroyed, making it difficult to help victims.
Tracking suspected contacts of Ebola victims remains a challenge in areas controlled by rebels.
Ebola can be transmitted between humans through blood, secretions and other bodily fluids of people – and surfaces – that have been infected.
The treatment of Ebola itself has taken an experimental turn in DRC, where scientists are now conducting a real-time study of how well pioneering drugs work.
More than 160 people there have already been treated with the drugs, and the way people are treated won’t change, but scientists will now be able to compare them.
Four experimental drugs are being used to try and combat the disease – mAb 114, ZMapp, Remdesivir and Regeneron.
Patients will get one of the four, but researchers won’t know which they were given until after the study.
Dr Jeremy Farrar, director of Wellcome, a UK charity who has funded research into the vaccine being used in the DRC, told MailOnline: ‘The Ebola vaccine and now also potential treatments available as part of clinical trials are having a huge impact.
‘But, we are in a crucial phase and it is an incredibly challenging and frightening environment for health workers. The next month, over the Christmas and New Year, will be critical to what happens to this outbreak.’
The outbreak has been plagued by security problems, with health workers attacked by rebels in districts where the virus has been spreading.
The WHO have said they are struggling to work with ‘non-engaged’ communities. Pictured, a woman cries during the funeral of a child, suspected of dying from Ebola December 17
Last week, officials announced more Ebola cases are being diagnosed in the city of Butembo, 35 miles (56km) away from Beni, where most of the outbreak is happening.
Experts warn the quick spread makes tackling the virus more complicated because containing it has been challenging enough in the one city.
They fear experimental vaccines which have been doled out to thousands of people, and have reportedly prevented the death toll rising into the thousands, will run out.
It comes after news broke last week that hundreds of health workers in South Sudan will be given Ebola vaccinations amid fears the virus will spread.
No cases have been confirmed in neighbouring South Sudan yet, but the country is on ‘high alert’, according to the World Health Organization (WHO).
More than 2,000 healthcare and frontline workers in the country will be offered a vaccine to try and stop the spread.
Teams of vaccinators are ready to conduct the vaccinations, starting in the capital, Juba, on December 19.
The UN Refugee Agency warned there is an influx of Congolese refugees seeking shelter in South Sudan because of conflict in the DRC.
Dr Farrar said: ‘This Ebola outbreak is taking hold in an incredibly complex region and extends into dangerous conflict areas.
‘The number of cases and deaths is concerning but the DRC public health teams, WHO and other international partners continue to provide an incredible response.’
WHAT IS EBOLA AND HOW DEADLY IS IT?
Ebola, a haemorrhagic fever, killed at least 11,000 across the world after it decimated West Africa and spread rapidly over the space of two years.
That epidemic was officially declared over back in January 2016, when Liberia was announced to be Ebola-free by the WHO.
The country, rocked by back-to-back civil wars that ended in 2003, was hit the hardest by the fever, with 40 per cent of the deaths having occurred there.
Sierra Leone reported the highest number of Ebola cases, with nearly of all those infected having been residents of the nation.
WHERE DID IT BEGIN?
An analysis, published in the New England Journal of Medicine, found the outbreak began in Guinea – which neighbours Liberia and Sierra Leone.
A team of international researchers were able to trace the epidemic back to a two-year-old boy in Meliandou – about 400 miles (650km) from the capital, Conakry.
Emile Ouamouno, known more commonly as Patient Zero, may have contracted the deadly virus by playing with bats in a hollow tree, a study suggested.
HOW MANY PEOPLE WERE STRUCK DOWN?
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Figures show nearly 29,000 people were infected from Ebola – meaning the virus killed around 40 per cent of those it struck.
Cases and deaths were also reported in Nigeria, Mali and the US – but on a much smaller scale, with 15 fatalities between the three nations.
Health officials in Guinea reported a mysterious bug in the south-eastern regions of the country before the WHO confirmed it was Ebola.
Ebola was first identified by scientists in 1976, but the most recent outbreak dwarfed all other ones recorded in history, figures show.
HOW DID HUMANS CONTRACT THE VIRUS?
Scientists believe Ebola is most often passed to humans by fruit bats, but antelope, porcupines, gorillas and chimpanzees could also be to blame.
It can be transmitted between humans through blood, secretions and other bodily fluids of people – and surfaces – that have been infected.
IS THERE A TREATMENT?
The WHO warns that there is ‘no proven treatment’ for Ebola – but dozens of drugs and jabs are being tested in case of a similarly devastating outbreak.
Hope exists though, after an experimental vaccine, called rVSV-ZEBOV, protected nearly 6,000 people. The results were published in The Lancet journal.