And as nature constantly reshuffles the genes in her microbial repertoire, new diseases or variations of old ones keep appearing in new places at an alarming rate. The "Nipah" virus jumped from pigs to humans in Malaysia in 1998, for instance, killing 105 people before being stamped out. West Nile virus swept across the U.S. last year, killing 277 people. "It is the nature of these organisms to change in order to survive," explains Dr. Jon B. Bruss, Pharmacia Corp.'s clinical director for infectious disease research in Kalamazoo, Mich. "As they change, they can become more pathogenic to humans." And as global urbanization and travel continue to increase, "this type of worldwide outbreak will be more prevalent," says Dr. Neil O. Fishman, director of health-care epidemiology and infection control at the University of Pennsylvania Medical Center.
SARS is the latest reminder that pestilence will always be a force to be reckoned with. Just a few weeks after a mystery virus was carried from China to Hong Kong, it has spread around the world, prompting unprecedented quarantines from Singapore to Canada (page 52). What is this disease -- and how worried should we be?What is SARS?
When infectious-disease experts first heard of a lethal respiratory disease spreading from person to person in Asia, they feared it could be the Big One they'd been dreading -- a rerun of the deadly 1918-19 influenza epidemic. That virulent flu killed more than 20 million people around the world, including an estimated 670,000 Americans. But tests showed the new ailment wasn't flu. For want of a better name, researchers dubbed it severe acute respiratory syndrome (SARS). Many now believe that it could be caused by a previously unknown variant of a family of microbes called corona viruses -- which they've found in infected people. Scientists who study the family say these bugs have the capability to mutate and create new strains. But the known bugs typically cause a mild cold at most, so some scientists still wonder if another microbe could be the real culprit.How does the disease spread?
It doesn't appear to spread as far or as fast as the flu virus, which can waft more easily through the air. At first, the infection was transmitted mainly in hospitals, at homes, and in one Hong Kong hotel. Researchers concluded that the virus spreads in droplets when victims cough. But there's evidence that it may survive on doorknobs or other surfaces for several hours, to be picked up when touched and transported to the mouth, nose, or eyes. And an outbreak in a Hong Kong apartment building raised fears that the virus could be transmitted through sewage or water systems.
Certainly, it can be highly contagious. Its rapid spread around the world "is alarming to a lot of people," says Dr. W. Michael Scheld, president of the Infectious Diseases Society of America (IDSA).How deadly is it, and how does it kill?
About 80% of those who fall ill manage to recover in a couple of weeks. But the rest get desperately sick. About 3% to 4% of those infected die.
The virus causes a fever, often accompanied by chills, headache, and body aches. After two to seven days, patients begin to cough. What's happening is that the capillaries in the lungs begin to leak fluid into the lungs themselves. In severe cases, the lungs fill up with so much fluid that patients can't get enough oxygen into their bloodstreams. Respirators can help -- but not always enough. Essentially, victims die from asphyxiation and lung damage, not from a massive inflammatory response to the pathogen (a phenomenon called sepsis) as in many other dangerous diseases.Are there any drugs that help?
Some doctors, especially in Hong Kong, believe that antiviral drugs like ribavarin, along with steroids, can ease symptoms. Others are skeptical. "We have no evidence, unfortunately, that any specific antiviral therapy, or steroid treatment, or other agents that are targeting this virus are of any benefit to patients," reports Dr. Julie Gerberding, director of the Centers for Disease Control & Prevention. In fact, some infectious disease experts fear that anti-inflammatory drugs could make things worse by dampening the body's immune response.
As soon as scientists nail down the viral culprit, researchers will quickly test the efficacy of existing drugs. And with innovative new approaches to making vaccines, it may be possible to read the genetic sequence of the virus and come up with vaccine candidates within weeks. But proving that a vaccine is safe and effective in people will take years.How does this epidemic compare with others, and how worried should we be?
As of Apr. 2, SARS had killed 78 people. In contrast, tuberculosis causes an estimated two million deaths a year, and malaria takes a similar toll. Garden-variety flu kills more than 250,000 people worldwide per year. "If you put it into perspective -- based on the knowledge we have now, and relative to other diseases we know -- it is not that bad," says Pharmacia's Bruss.
However, there are two reasons to be worried. First, SARS is new, and there are many unanswered questions. "We don't know the full modes of transmission, or how quickly it can spread," says Bruss. And SARS is alarming for another reason: It spreads from person to person. People get West Nile disease mainly from virus-containing mosquitoes, not from neighbors. In the Nipah outbreak, victims only got the disease from pigs. AIDS and hepatitis C can be avoided by shunning dirty needles or high-risk sex. In contrast, it's possible to get SARS in the process of daily life -- being on a certain plane, or lodging in a certain hotel. "We may be in the very early stages of what could be a much larger problem," warns the CDC's Gerberding:Can we keep it from spreading in the U.S.?
"That's the key question -- which we don't know the answer to," says Barry R. Bloom, dean of the Harvard School of Public Health. So far, all the known U.S. cases involve people who had been to Asia, their close family members, or health-care workers. Public health officials hope that measures such as immediately isolating anyone with symptoms will limit the spread.
Many doctors expect the epidemic to burn itself out eventually. As patients recover and gain immunity to the virus, the bug runs out of people to infect. But given the human grief and economic havoc the disease is already causing, that's hardly a cheering prospect. By John Carey in Washington, with Amy Barrett in Philadelphia and Arlene Weintraub in Los Angeles