Viruses mutate billions of times a day, over the entire world, and have done so throughout history. Most of the mutations are fatal to the virus, and of the small percentage that are not, most have very little effect on the virus or its host at all. The extremely small percentage of cases where the virus actually acquires a significant new characteristic represent the general source of continuing viral infections in animals, including man.
Your body eventually learns to kill viruses on its own, unless you die. So does the body of every duck in China. Given that there are several billion ducks in China, and the additional coincidence that those ducks tend to live in close proximity to both pigs and humans, it ends up being the ducks that matter more. One of the things a mutation can do is to allow a virus that previously lived only in ducks to survive in pigs. In one in a hundred thousand cases of such species change, it can happen that the same mutation or a subsequent one will allow the virus to live in humans. In one case, recently, it is believed that a virus may have moved directly from ducks and chickens, to humans.
This phenomenon, called zoonosis, creates a source of new viral infection agents among humans. By itself it really doesn’t make a lot of difference, and until the last century, it was mostly a once a century thing for a new plague to sweep across a large population of humans. Without a vector that crossed large distances in a short time, the virus would die out with its most susceptible victims, and the remaining population would have some immunity to it, thereafter.
The common cold, for instance, is not a single disease, caused by a single virus. It is a description for a set of symptoms caused by a group of viruses, and has often been applied to other viral agents, some of which later cause other symptoms. Viral Pneumonia is such a disease, in some cases. Antibiotics do not affect viruses, although they can prevent, or cure subsequent microbial infections that opportunistically exploit weakened victims.
In the last hundred years the picture has changed dramatically. There is no place on earth that is not now visited by people from far away on at least an occasional basis. The Tibetan Monasteries are tourist attractions, and the Headwaters of the Amazon have regular boat traffic. These places are in turn connected by Airports, and regular flights, so that the entire world now lives a day and a half from your front porch. The duck that Cho sells in Guodong Province on Monday, is butchered by a chef in Hong Kong, that afternoon, and the tourist who ate the salad he sneezed over flies back to Toronto the next morning. When he comes down with SARS, he checks into a hospital there.
And in Hanoi, another person returns from Beijing, from the international hog farmers’ convention. That Thursday, two computer programmers from Tokyo return from their sales meeting in Shenzen with the same new disease, but both of them have very high resistance. They just go on working, although they sneeze a lot. Their company sends out it sales teams to Switzerland, Kenya, and Brazil on Monday. The same first week after zoonosis that would have seen five people in a farming village get sick, has, in the twenty first century infected people on five continents. And so far, it’s just a dozen people with severe colds. One got pneumonia, and may die. No one has even given this new disease a name. In fact, no one even knows it is a new disease yet.
The duck thing is just a forinstance. Chickens or iguanas could do it, or fleas, or frogs. Hogs are similar in chemistry enough to be a good intermediary step for viruses, but so are horses, and chimpanzees. Measles, mumps, and various poxes have done it in the past, each coming from a species domesticated by man.
The only thing that has changed is that man is now his own best vector. We are healthy. We are strong. And we go everywhere, all the time. We do it even when we are a bit under the weather. After all, it’s just a cold. Aspirin, fluids, and rest. “I’ll sleep on the plane.”
Tris
“Here Kitty, Kitty, Kitty.” ~ Erwin Schrodinger ~