In a ramshackle village in South Sudan, just a few miles from the Ethiopian border, at least three people were reported to have fallen gravely ill on Friday.

The source of their illness remains unknown, but there are telltale signs of what it could be: vomiting, diarrhoea, high fevers, and bleeding.

A biorisk alert, issued by Airfinity, a company tracking dangerous disease outbreaks around the world, suggests the patients could be infected with Ebola

“Health authorities, alongside a WHO team, reported three suspected viral haemorrhagic fever cases in Lotimor, South Sudan ”, the alert warned.

“Symptoms [are] consistent with viral hemorrhagic fever,” it added.

Outbreaks like these are becoming increasingly common. Haemorrhagic outbreaks of Ebola and Marburg go back 50 years, but now their frequency is increasing.

Data analysed by The Telegraph found that clusters of Ebola and Marburg have increased significantly decade-on-decade since the 1960s.

Last year alone, there were three Ebola outbreaks (one each in the Democratic Republic of Congo, Uganda and Ethiopia) and two Marburg outbreaks, in Tanzania and Ethiopia.

Excluding the events in South Sudan, which are yet to be officially determined, there have been 15 such outbreaks of Ebola and Marburg virus since 2020.

The decade before, there were 11 – the most famous of all the 2014 West Africa Ebola outbreak, killing more than 11,000 people.

“Outbreaks of diseases like Ebola were once sporadic,” says Laura Appleby, head of epidemiology and preparedness at the Coalition for Epidemic Preparedness Innovations (CEPI).

“However, since 2010, an outbreak of a filovirus, the family to which Ebola, as well as its deadly relatives, Marburg and Sudan, belong, has occurred every year almost exclusively in Africa, and the diseases are extremely lethal.

They are “not only occurring more frequently but also becoming more widespread”, she added. “Last year Ethiopia reported its first-ever Marburg outbreak.”

Between 2014 to 2016, Ebola wreaked havoc in West Africa, infecting more than 30,000 people across Liberia, Sierra Leone and Guinea, killing roughly 11,000.

That outbreak now hangs over all discussions of Ebola and its cousins. It triggered major advances in the management of the disease but the increasing frequency of new outbreaks is raising difficult questions for epidemiologists.

First, is the uptick in the data real or are we just getting better at spotting new outbreaks?

And second, could a confluence of circumstances lead to a super-spreader event and another large scale outbreak of the type seen in west Africa a decade more than a decade ago?

Ebola and Marburg have long been known to live in bats and other mammals in Africa and occasionally jump to humans.

Bats, monkeys and antelope, are reservoirs for the viruses and people have become infected after coming into close contact with them or eating them.

Scientists worry that as populations increase and people clear forests for farmland, humans come into more contact with the animal-borne viruses.

“There’s definitely increasing infection pressures and transmission,” says Trudie Lang, professor of global health research at the University of Oxford.

“The driver of more outbreaks is movement of people, a real pressure driven by climate change, movement of vectors, and changing social demographic pressures.

“That jump between humans and animals is really important, and so changing habitat, changing pressure on sources of food, all of those pieces are really important.”

Recent outbreaks clearly demonstrate the link, says Dr Appleby at CEPI.

“Activities like deforestation, mining, agriculture, handling bush meat and urban expansion are bringing people into closer contact with bats, the filovirus host,” she says.

“For example, the 2024 Rwandan Marburg outbreak has been traced back to a miner in a tin mine where bats were found.

“Encroachment not only increases the contact between people and bats, but it could also push them out of their habitats and cause them to forage in agricultural areas or near homes, creating new opportunities for transmission.”

The other potential worry is if Ebola or Marburg mutated to be able to spread through the air – like Covid-19 or an influenza – instead of through direct contact with the bodily fluid of a victim, which slows its spread somewhat and currently renders the viruses relatively more containable.

But a strain of Ebola, known as Reston, has shown evidence of airborne transmission.

It currently is known only to infect animals, although it has repeatedly been found in the upper respiratory tract in pigs – animals that have long been regarded as one of the greatest zoonotic threats to public health because of their cells, which allow viruses to mix and mutate, creating strains capable of causing human pandemics.

There are not only more opportunities for the virus to jump from animals. Scientists are increasingly becoming aware that the virus can stay in humans long after they have recovered.

Male Ebola survivors can harbour the virus in their testicles for up to five years, representing a new potential reservoir of infection.

Yet at the same time, governments across Africa are much more prepared, says Prof David Heymann, who worked on the international response to the first outbreaks in the 1970s.

Prof Heymann, now at the London School of Hygiene and Tropical Medicine, said governments were better at looking for the viruses, and their laboratories were much better at detecting them.

That could account for some of the increase, by recording outbreaks that would once have gone undetected, experts say.

But it is not clear.

“What’s good news is the world has definitely stepped up to surveillance and reporting, and most of these countries have got really pretty good systems now for reporting these are notable diseases and having these systems,” says Oxford’s Prof Lang.

“So that’s really excellent, but we can’t really split out whether, because we’ve not got that sort of baseline, we really can’t split out if [outbreaks] are increasing or if we’re getting better at measuring them.”

Good surveillance will be key to making sure any future outbreak cannot spiral into the sort of epidemic seen a decade ago. In 2014, the outbreak started in a cross-border trading area and it took the authorities three months to diagnose what was happening.

The most troubling scenario would be if one of the viruses flared up again in an unprepared or difficult-to-reach area, particularly places affected by war and conflict.

“If you’ve got a layering of really impoverished, marginalised areas, lack of access to the best scientific interventions, ability to do that, all of those things, we could definitely be at really high risk,” says Prof Lang.

Miles Carroll, Professor of Emerging Viruses at Oxford, agrees.

“Nowadays, it depends if it’s in a war zone and you can’t get diagnostics there and people in to assist and who can’t get in, then obviously it could definitely bubble out of control before it was shut down.”

The big difference between then and now is the potential availability of vaccines. The first Ebola vaccine became available in 2015 with the outbreak well underway. There are now two Ebola vaccines available and candidates for a Marburg vaccine are undergoing trials.

If these jabs could be given quickly to patients’ close contacts in a future outbreak – something called a ring vaccination strategy – then it could stop the spread in its tracks.

“The vaccine definitely helps, says Prof Carroll. “We certainly did not have the vaccine [during the outbreak], we got it at the tail end.

“Also better lessons learned from the past, getting the confidence of the local communities to come forward with cases and not hide them. I think it all helps.”

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