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Why Pauline Cafferkey's Ebola case is unprecedented

Pauline Cafferkey has had one of the most unprecedented cases of Ebola ever recorded by medical science.

After clearing the illness from her body once, at the height of the Ebola outbreak in the winter of 2014-15, Pauline was laid low by the virus again, almost a year later.

At the University of Glasgow, I met Dr Emma Thomson for ITV News, the doctor who led the cutting-edge scientific team that worked tirelessly to find out how to help Pauline and work out what was wrong.

"Pauline's case was already an unusual case,” Dr Thomson told me.

“She had one of the highest viral loads ever recorded during her first illness so unusual things can happen in that situation, so if you had someone who had very high viral load, it might be possible the virus might behave in a different way.”

One of Pauline's brain scans. Credit: ITV News

In Pauline Cafferkey, the Ebola virus did something never seen before - it leaked from her blood into her cerebrospinal fluid (which bathes the spine and the brain). There, the Ebola virus lurked for months, slowly growing in numbers, even after it had been cleared from Pauline’s blood.

Almost eight months after she had left the Royal Free Hospital in London, Pauline was once again admitted to the isolation unit there. This time she had meningitis, caused by the Ebola virus inflaming the membrane around her brain.

Doctors had never seen anything like it. To try and understand how the Ebola virus might have changed in Pauline’s body between her two visits to the Royal Free hospital, Dr Thomson’s team turned to cutting-edge genetic technology.

Their next-generation sequencing system was able to identify millions of strands of RNA and DNA in samples of Pauline’s blood and cerebrospinal fluid, all in 24 hours. From that mountain of data, Dr Thomson’s team worked around the clock to sift out and identify and examine the tiny Ebola sequence.

Officials dealing with the outbreak in Sierra Leone. Credit: Reuters

To their surprise, they found that the virus had hardly changed at all over the course of the eight months between Pauline’s hospital admissions.

Viruses such as Ebola are made from RNA (a single-strand version of DNA) and they continually mutate, every time they divide and multiply.

The fact that Pauline’s virus had changed so little meant that it had been replicating extremely slowly.

Fortunately, that insight also meant that Dr Thomson could assure Pauline’s doctors that the treatments that had worked for her before would probably work again.

Pauline Cafferkey's case will give scientists pause for thought about how Ebola spreads, and might still be lurking, in places where it is endemic, such as West Africa.

“Pauline’s case was a landmark case, we’d never seen anything like it anywhere else in the world, even in the many tens of thousands of survivors in West Africa this presentation had not been seen before,” says Dr Thomson.

“No other patient has had a relapse of Ebola virus 10 months after their infection. It does mean that we need to be aware that patients who are survivors of Ebola virus infection need to be monitored and if they develop meningitis symptoms, certainly we would want to think carefully about whether or not the virus was hiding within the central nervous system.”

Pauline is now free from the Ebola virus, as far as doctors can measure.

But Dr Thomson said they had to acknowledge that this was “uncharted territory” and that they would have to continue to monitor Pauline carefully.

“It’s certainly just possible that Pauline could become unwell again but, we think, extremely unlikely.”