Thread by @kakape

Some stunning and very worrying #Ebola science out today, suggesting the ongoing outbreak in Guinea is not due to fresh spillover from nature, but the virus has persisted in humans since the devastating epidemic in 2013-2016.

Story here, thread to come:
sciencemag.org/news/2021/03/n…

Three groups of researchers posted sequencing data from #Ebola patients in the Guinea outbreak on virological.org today. Two groups each have sequences from four patients, the other from two. It’s unclear how much overlap there is (I suspect a lot)
virological.org/c/ebolavirus/g…

Looking at the virus sequences, all three groups reached the same conclusion: The outbreak was caused by the Makona strain of Ebola Zaire, the same strain that caused the devastating outbreak in West Africa that started in 2013.

But more than that. The sequences fall in the middle of the sequences from that outbreak, making it extremely unlikely that this is a separate introduction from a natural reservoir.
Here is a phylogenetic tree - essentially a family tree of viruses - that shows this well:

While the branch with the new sequences looks long, it is actually very short considering the virus had 5 years to accumulate mutations.
Instead of more than 100 it has only amassed 12 changes over the years. That's why researchers suspect the virus was “lying low” in someone.

Such latency in #Ebola is not completely new. A 2016 resurgence in Guinea started with a survivor who still shed the virus in his semen after more than 500 days and infected a partner (ncbi.nlm.nih.gov/pmc/articles/P…).
But 5 years? "This is pretty shocking,” as @angie_rasmussen told me.

@angie_rasmussen This obviously raises a lot of important and interesting scientific questions, like: How common is this? How exactly does the virus persist? Can it be eradicated? How?
But the most worrying part for me is what this means for survivors of this dreadful disease.

@angie_rasmussen #Ebola survivors have gone through a terrible experience. On top of the grief and the trauma, many suffer from sequelae from the disease and already face stigmatisation. As @DrMikeRyan said at today’s presser: “The survivors deserve our support. They’ve been to hell and back."

@angie_rasmussen @DrMikeRyan I worry that this news will mean even more suffering for them. So it is really important to remember that from what we know so far such transmission appears to be a very rare event and that while unprotected sex may pose a risk, casual contact does not.