The case of Pauline Cafferkey, the first person known to have recovered from Ebola and then suffer an apparently life-threatening relapse, is taking scientists into uncharted territory. The Scottish nurse’s critically ill situation, described as “staggering” by one British virologist, signals just how complex and formidable a foe the Ebola virus may turn out to be now that scientists have the chance to study its survivors. Previous studies and preliminary data from research in survivors of the vast West African outbreak have detected Ebola virus in semen, breast milk, vaginal secretions, spinal fluid and fluids around the eyes.

But scientific literature has never documented an Ebola relapse case before, meaning Cafferkey’s is likely to generate great fear and anxiety for the 17,000 or so other Ebola survivors across West Africa. “This is totally unprecedented. We’ve never seen this, and there’s so much uncertainty,” said Jeremy Farrar, a specialist in infectious diseases and director of the Wellcome Trust. “Is this a one off? A very rare event? Or is this going to be quite common? The honest answer is we don’t know.” CONTINUE