How progress makes us sick--Advances that make life more comfortable can also make it more dangerous
News You Can Use Thew Week, By Geoffrey Cowley
SARS may dominate the headlines, but it isn't the only weird disease on the World Health Organisation's radar screen. In central Africa, an outbreak of the dreaded Ebola fever has stretched into its fifth month. In Belgium and the Netherlands, a virulent new strain of avian flu wiped out entire chicken farms. Dutch farmers recently slaughtered 18 million birds in hopes of stopping the outbreak. Yet the bird flu spread to several provinces and jumped from poultry to pigs and even people, causing 83 human cases. Most of the infected people suffered only eye inflammation, but some developed respiratory illness.
N I P A H The virus is named after the location in Malaysia where it was first detected. Certain species of fruit bats, the natural hosts of the virus, passed it on to pigs, which transmitted to humans
SARS. Ebola. Avian flu. The parade of frightening new maladies continues, each one confirming that our species, for all its cleverness, still lives at the mercy of the microbe. It did not seem that way 30 years agoÑnot with smallpox largely defeated, AIDS still undreamed of and medical science evolving at an unprecedented clip. But even as optimists proclaimed victory over the germ, our mega cities, factory farms, jet planes and blood banks were opening broad new avenues for infection.
The dark side of progress is now unmistakable; many of the advances that have made our lives more comfortable have also made them more dangerous. Some 30 new diseases have cropped up since the mid-1970sÑcausing tens of millions of deathsÑand forgotten scourges have resurfaced with alarming regularity. Health experts declare that infectious diseases will continue to emerge and warn that complacency and inaction could lead to more contagion. So what is to be done? As the SARS outbreak has shown, surveillance is critical. By spotting new infections wherever they occur, and working globally to contain them, we can greatly reduce their impact. But is preparedness our ultimate weapon? Do we know enough about the genesis of new diseases to prevent them? Could we avert the next SARS? The next AIDS? What would a reasonable strategy look like?
A V I A N F L U Avian flu was thought to infect birds only until it jumped the species barrier in 1997. However, the transmission of the virus from birds to humans is a rare event.
We do not hold all the cards in this game. Most new diseases begin when a person catches something from an animalÑa transaction shaped by chance or even the weather. When healthy young adults started dying of a SARS-like syndrome in New Mexico 10 years ago, it took health experts several weeks of intensive lab work to identify the culprit. To the scientists' amazement, it wasn't a human pathogen at all. It was a novel member of the hantavirus family, a group of rodent viruses that sometimes spread through the air after rats or mice shed them in their urine. The previous outbreaks had occurred in Asia. So why were people dying in New Mexico? Scientists now believe the American mice had harboured the virus all along but had never been populous enough to scatter infectious doses in people's toolsheds and basements. What changed the equation that year was El Nino. The ocean disturbance caused an unusually warm winter in the southwest. The mouse population exploded as a result and the hantavirus got a free ride.
Until someone harnesses the jet stream, such accidents are sure to happen. But quirky weather is not the greatest threat we face. As ecologists study the causes of disease emergence, they are finding that human enterprise is a far more significant force. Almost any activity that disrupts a natural environment can enhance the mobility of disease-causing microbes. Consider what happened in the 1980s, when farmers in Venezuela's Portuguesa state cleared millions of acres of forest to create cropland. The farms drew as many rats and mice as people, and the rodents introduced a deadly new virus into the region. The so-called Guanarito virus causes fever, shock and haemorrhaging. It infected more than 100 people, leaving a third of them dead.
Malaysian pig farmers had a similar experience in 1999, after they started pushing back the forest to expand their operations. As barns replaced forestland, displaced fruit bats started living in the rafters, bombarding the pigs' drinking water with a pathogen now known as the Nipah virus. The pigs developed an explosive cough that became known as the one-mile cough because you could hear it from so far away. The virus soon spread from the pigs to their keepers, causing extreme brain inflammation and killing 40 per cent of the affected people. The outbreak ended when Malaysian authorities closed eight farms and slaughtered a million pigs.
H A N T A Hanta viruses are carried by rodents, especially the deer mouse. You can become infected by their droppings, and the first signs of sickness (fever and muscle aches) appear one to five weeks later.
The point is not that rain forests are dangerous. It is that blindly rearranging ecosystems can be hazardous to our health. That is where Lyme disease emerged, and it, too, is a product of the way we use our land. The bacterium that causes Lyme lives in the bodies of deer and white-footed mice, passing between those animals in the heads of biting ticks. People have crossed paths with all these critters for generations, yet the first known case of Lyme disease dates back only to 1975. Researchers tied the event to suburban development. In open woodlands, foxes and other predators keep a lid on the Lyme agent by hunting the mice that carry it. But the predators vanish when developers chop woodlands, and the mice and their ticks proliferate unnaturally.
The problem is particularly serious in the case of infections we get from primates and pigs. When the Ebola virus jumps from an ape into a person, it often races through a family or a hospital before burning itself out. And HIV is still spreading steadily after three decades of person-to-person transmission. It has infected some 60 million people since crossing over from chimpanzees, and its emergence was no fluke of the weather. We placed ourselves in the path of the virus, we moved it around the world, and we are well poised to do it again.