Fears that Ebola ‘lurks under the radar’ of immune system as new cases linked to past outbreak

The new Ebola outbreak in the Democratic Republic of Congo may be linked to the second deadliest in history, sequencing has shown, raising questions about how long the virus can lurk “under the radar” of the immune system.

Health authorities in North Kivu, a region close to the border with Uganda and Rwanda, are scrambling to contain the highly contagious haemorrhagic fever after a three-year-old boy died last week.

There are suspicions that he caught the virus from neighbours in the densely-packed city of Beni, sparking fears that more cases may crop up in the coming days and weeks. The World Health Organization (WHO) has launched a vaccination campaign and at least 170 contacts have so far been isolated.

Virus sequencing, carried out by scientists at the University of Kinshasa, has shown that the new confirmed infection may be linked to a protracted epidemic in the region between 2018 and 2020, when nearly 2,300 people died.

Sequencing has suggested the case is “closely related” to samples taken around July 2019, with just six mutations over 28 months, according to a paper published on

“This case represents a new flare-up event from the 2018-2020 outbreak, and is not linked to the February 2021 flare-up, nor a new spillover event,” the scientists said.

The results are “really, really weird”, according to Dr Angela Rasmussen, a virologist at the Vaccine and Infectious Disease Organisation at the University of Saskatchewan in Canada.

Ebola is an RNA virus, a family of viruses known to mutate rapidly and which generally do not persist in a latent state in humans.

Yet the genome of the latest sample has “barely changed” in the last two years, suggesting Ebola can lurk in survivors for longer than previously thought and demonstrating just how much scientists still have to learn about the disease, first detected in 1976.

“That’s why this is so stunning and scientifically fascinating,” Dr Rasmussen wrote on Twitter. “This hints at an unknown and completely novel persistence mechanism for an RNA virus.” 

The finding comes after the WHO said in March that a “persistently infected survivor” of the 2013 to 2016 Ebola epidemic in West Africa may have sparked an outbreak in Guinea – this was swiftly contained but 23 people were infected, 12 of whom died.   

The long time-frame between the two outbreaks led experts to initially believe that the latest cases were a result of a new spillover event. However, the genetic sequences were so similar that there must be a link, experts said.

Ebola can persist in bodily fluids after an infection, particularly the semen, and male survivors are urged to practise safe sex until their semen has tested negative. But it is unusual for patients to still be infectious after around six months.

Dr Rasmussen said the two incidents “upend” the idea that Ebola doesn’t persist “under the radar of the host’s immune system”. Speaking to the Telegraph, she added that it is not surprising that this is only emerging now, particularly as scientific advances mean Ebola is now treatable so more people survive it.

“We really didn’t appreciate that persistence occurred in Ebola survivors until the West African epidemic, because before that most Ebola outbreaks involved 100-200 people at most, and with such high mortality rates that meant few survivors to follow,” she said.

“Add to it that often these outbreaks occurred in remote, rural areas and there’s often not a lot of scientific infrastructure enabling sensitive molecular testing, and no funding for that type of work, and that makes it very hard to observe something like this.”

Dr Rasmussen added that longer term studies into Ebola survivors and boosting scientific infrastructure in the regions that tend to be hit by the virus will be critical to solve the riddle.

“Understanding the risk of silent, persistent Ebola infection will be essential to stopping these outbreaks [in future],” she said.

At the time of the Guinea outbreak Dr Mike Ryan, WHO’s director of emergencies, said: “The vast majority of people who survived Ebola cleared the virus from their system, and they recover within six months.

“An even tinier proportion of people end up potentially carrying the virus. They’re not infectious to other people, except in very particular circumstances, and a tiny proportion of them can relapse and become sick again,” he said. 

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