Some viruses can play a deadly game of hide and seek inside the human body

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 sem