A Planet of Viruses - Carl Zimmer [29]
The virus started in Chinese bats. A lineage of the viruses then began to spill over into a catlike mammal called a civet. Civets are a common sight in Chinese animal markets, and it’s likely that humans became spillover hosts as well. The virus then evolved the ability to leap from human to human. SARS was a very young virus when scientists discovered it, and the speed at which it was discovered helped make it a relatively small outbreak. Scientists were able to identify and quarantine people with the disease, and they banned the sale of civets in markets. Although the SARS virus managed to spread across much of the world, it only caused about eight thousand cases and nine hundred deaths before it disappeared.
We can expect more viruses to sweep into our species, and they will probably come at an accelerating pace. Animals in remote parts of the world have harbored exotic viruses for millions of years, and for all that time humans have had little contact with them. Now humans are moving deep into these remote territories to harvest timber, dig mines, and establish new farms. And in the process, they’ve come into contact with new viruses. Nipah virus, for example, causes dangerous inflammation of the brain in its victims in Southeast Asia. It’s a virus that normally lives in bats, which once lived far from humans in jungles. Now the bats—and the viruses—have no jungles to live in.
There’s no reason to think that one of these new viruses will wipe out the human race. That may be the impression that movies like The Andromeda Strain give, but the biology of real viruses suggests otherwise. 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. Once an Ebola outbreak ends, the virus vanishes for years.
Ebola-like viruses may be frightening, but they probably pose less of a danger to our species than viruses with a lower death rate that can spread to more hosts. The 1918 outbreak of influenza killed only a tiny fraction of its victims. But because it infected one in three people on Earth, that tiny fraction added up to an estimated fifty million people. HIV crept slowly and surreptitiously around the planet before it was first detected. Instead of causing the terrifying symptoms of Ebola, HIV quietly breaks down the immune system over the course of many years.
We don’t know which virus will create the next great epidemic, in part because we don’t know the world of viruses very well. GVFI scientists have discovered a number of new viruses in African monkeys. Their tests on hunters have revealed those viruses in humans as well. Fortunately, these new viruses cannot yet spread from person to person. But that doesn’t mean that we can simply ignore them. Just the opposite: these are the viruses we need to block before they get a chance to make the great leap into our species.
The Long Goodbye
Smallpox
We humans are good at creating new viruses by accident—whether it’s a new flu virus concocted on a pig farm, or HIV evolving from the viruses of butchered chimpanzees. What we’re not so good at is getting rid of viruses. Despite all the vaccines, antiviral drugs, and public health strategies at our disposal, viruses still manage to escape annihilation. The best we can typically manage is to reduce the harm viruses cause. HIV infections, for example, have declined in the United States, but fifty thousand Americans still acquire the virus every year. Vaccination programs have eliminated some viruses from some countries,