A Planet of Viruses

“Viruses are not living organisms,”

Viruses wreak chaos on human welfare, affecting the lives of almost a billion people. They have also played major roles in the remarkable biological advances of the past centur

Viruses are indeed exquisitely deadly, but they have provided the world with some of its most important innovations. Creation and destruction join together once more.

Many scientists now argue that viruses contain a genetic archive that’s been circulating the planet for billions of years. When they try to trace the common ancestry of virus genes, they often work their way back to a time before the common ancestor of all cell-based life

When mimiviruses invade amoebae, they don’t dissolve into a cloud of molecules. Instead, they set up a massive, intricate structure called a viral factory. The virus factory takes in raw ingredients through one portal, and then spits out new DNA and proteins through two others. The viral factory looks and acts remarkably like a cell. It’s so much like a cell, in fact, that La Scola and his colleagues discovered in 2008 that it can be infected by a virus of its own. It was the first time anyone had found a virus of a virus. It was yet another thing that ought not to exis

Forced to carry tiny genomes, viruses could not make room for genes that did anything beyond make new viruses and help those viruses escape destruction. They could carry genes to let them eat, for example. They could not turn raw ingredients into new genes and proteins on their own. They could not grow. They could not expel waste. They could not defend against hot and cold. They could not reproduce by splitting in two. All those nots added up to one great, devastating Not. Viruses were not alive

In the late 1700s, the British physician Edward Jenner invented a safer smallpox vaccine based on stories he heard about how milkmaids never got smallpox. Cows can get infected with cowpox, a close relative of smallpox, and so Jenner wondered if it provided some protection. He took pus from the hand of a milkmaid named Sarah Nelmes and inoculated it into the arm of a boy. The boy developed a few small pustules, but otherwise he suffered no symptoms. Six weeks later, Jenner variolated the boy—in other words, he exposed the boy to smallpox, rather than cowpox. The boy developed no pustules at all. Jenner published a pamphlet in 1798 documenting this new, safer way to prevent smallpox. He dubbed it “vaccination,” after the Latin name of cowpox, Variolae vaccinae.

The first effective way to prevent the spread of smallpox probably arose in China around AD 900. A physician would rub a scab from a smallpox victim into a scratch in the skin of a healthy person. (Sometimes they administered it as an inhaled powder instead.) Variolation, as this p

Variolation, as this process came to be called, typically caused just a single pustule to form on the inoculated arm.

Ebola, for example, is a horrific virus that can cause people to bleed from all their orifices, including their eyes. It can sweep from victim to victim, killing almost all its hosts along the way. And yet a typical Ebola outbreak only kills a few dozen people before coming to a halt. The virus is just too good at making people sick, and so it kills its victims faster than it can find new ones.