NPR Viruses are tiny — and sneaky.
So sneaky that some play a deadly game of hide and seek. The “seek” part is all too familiar: They’re always looking for ways to infect humans. Their ability to hide is far less well-known and can have devastating implications.
The human body holds several effective hiding spots that some of the world’s nastiest viruses have discovered — like the eyes and the testes — that are beyond the reach of the immune system. It’s here that submicroscopic viral RNA can safely linger.
Often the human hosts have no idea. They’d fallen ill, then appeared to beat the virus. Their blood tested negative. They show no symptoms. But that hidden virus is capable of springing back into action. It can emerge from hiding — either sickening the original host or slipping into semen or breast milk and infecting someone new.
Which viruses have mastered this technique? A number of notorious ones from Zika to measles to highly deadly viruses like Nipah, Marburg and Lassa fever.
And the virus that terrified the world in 2014: Ebola.
In the decade since, the Democratic Republic of Congo has experienced more than its fair share of Ebola crises — with nine outbreaks, including one that is ongoing — and more than its fair share of hidden viruses that spring back into action.
“Almost all the outbreaks recently — maybe not every single one of them but the vast majority — are traced back to a previous outbreak,” says Dr. Elizabeth Higgs, who is with the Division of Clinical Research at the National Institute of Allergy and Infectious Diseases. She says once the genetics of the virus are sequenced it is clear that many of the outbreaks haven’t come from an animal — like a bat — but from a human who unwittingly carried the virus after surviving a previous outbreak.