Closing in on a Mysterious Killer

By MICHAEL D. LEMONICK

People who think they're coming down with the flu, especially those living in the Southwest, should beware: the aches, fevers and coughs could mean something far worse. A mysterious ailment emerged last spring in which flulike symptoms become life threatening as tiny blood vessels throughout the lungs begin leaking plasma. Gasping for breath, victims literally start to drown in their own body fluids. The outcome in 27 of the first 45 known cases of the illness has been a quick death.

Unofficially called Four Corners disease, because it was first identified in the region around the intersection of Arizona, New Mexico, Colorado and Utah, the malady has now turned up in 12 states, from Oregon to Texas. At first, no one knew why so many men and women -- often young and otherwise healthy -- were dropping dead. But months of swift and skilled medical detective work have confirmed the cause of the outbreak -- and provided hope that it will not spread farther.

Within a few weeks after the first cases appeared, scientists suspected that the culprit was a variety of hantavirus, closely related to pathogens already known to exist in Europe and Asia. Researchers then established that the virus was carried by wild deer mice, and residents of the Southwest and West began taking special precautions to minimize their contact with the rodents. Finally, just over a week ago, scientists at the Centers for Disease Control in Atlanta and the Army Medical Research Institute at Fort Detrick, Maryland, reported that both institutions had independently isolated the virus and grown it under laboratory conditions -- a major step toward creating diagnostic tests and vaccines.

The danger seems to have receded for the moment. The death rate has dropped from 60% of victims to 35%, and only three cases were reported in the Four Corners region in the past month, none of them fatal. Increased public awareness and a drop in the deer-mouse population may have helped stem the spread of the disease. But researchers fear that cold weather will cause mice to seek shelter inside houses, exposing people once again. So a major multilingual public-information campaign, set in motion in the spring, will continue. And in January Army scientists will begin testing a vaccine developed to fight the Asian version of the virus, which may prove at least partially effective in halting the local virus as well.

The first inkling that a dangerous new disease was on the prowl came last May, when a 19-year-old Navajo man was rushed to an emergency room at the Indian Medical Center in Gallup, New Mexico. He seemed to have the flu, but suddenly he couldn't breathe. Within a short time, he was dead. Doctors recalled that they had seen a similar case about a month earlier. Then they found out that the young man had been on his way to his fiance's funeral when stricken -- and that she too had died in exactly the same way.

Further investigation uncovered two more cases, and after local health authorities ruled out severe flu and pneumonic plague -- the latter is endemic to the Southwest, and a few cases show up every year -- they turned to the CDC for help. Recalls Dr. C.J. Peters, chief of the CDC's Special Pathogens Branch: "It didn't fit the pattern of anything we'd seen, and all we could figure is that it was something brand new."

The scientists hoped, though, that whatever pathogen was responsible would be related to some known virus. Sure enough, only days after they began testing one agent after another, researchers triggered an immune response in victims' blood and tissue samples with a strain of hantavirus. That came as a surprise. While hantaviruses had been known to exist in the Americas, they had never been found to cause disease. They do afflict some 200,000 people a year worldwide. The majority of victims are in Asia, but Europe has hundreds as well. While these cases also start with flulike symptoms, the cause of death -- which happens 5% to 15% of the time in Asia and just 1% in Europe -- is often kidney hemorrhage, not fluid in the lungs.

The fact that Four Corners disease -- or Hantavirus Pulmonary Syndrome, as the CDC now calls it -- seems to have appeared out of nowhere might suggest that the virus just arrived in the U.S. But after testing deer mice in the Four Corners area and in other regions, investigators say it's been around for a long time. "In all cases," says Peters, "we found what was clearly the same viral species. Things don't spread that widely all of a sudden. It takes awhile for it to happen."

Then why hasn't the disease shown up in humans before? It probably has. People die from respiratory infections all the time; some cases that have been labeled "unexplained" were undoubtedly caused by hantavirus. The Navajo even have a traditional taboo against mice, which are believed to bear strange illnesses. The reason the outbreak was severe enough to be noticed this time, say investigators, is that heavy rains produced an unusually rich crop of wild pinon nuts, which in turn triggered a mouse-population explosion. When the animals urinate or defecate, the virus is spread into soil or dust that can then be inhaled by humans. In China cases multiply during harvest time, when farmers churn up the soil. As soon as health officials linked Four Corners $ disease to rodents, they launched an education campaign. They put together pamphlets, posters, videotapes and slide shows in English, Spanish and Navajo, explaining how to avoid contamination, and distributed them to churches, schools, public-health workers and exterminators.

Because hantaviruses are species specific -- that is, each strain is carried solely by one species of rodent -- there's little danger that deer mice will pass the virus on to, say, rats who frequent large urban areas. But deer mice are found in every part of the country except the Southeast and East Coast. Researchers are now trying to determine just how widespread the virus is. Says Dr. Howard Levy, a professor at the University of New Mexico School of Medicine, who has treated a number of victims: "We are certainly hoping this has been an isolated disease related to an increase in the rodent population last spring. But it probably will be with us forever."

Plenty of other questions remain. No one knows, for example, how long the incubation period inside the human body lasts (the current best guess is a couple of weeks). It's not clear why death comes so quickly -- in as little as four hours after respiratory symptoms begin. And the fact that no one under age 12 has come down with the disease is unusual, given that children's immune systems are less well developed than those of adults. That may indicate that the damage comes not from the virus itself but from the body's violent immune response to it.

The good news, says Peters, is that "we've not seen any evidence this can be passed from human to human." That means there is little chance of anything as extensive as the AIDS epidemic, in which hundreds of thousands of Americans have become infected. But few people who come down with chills and coughs in the Western U.S. this season will he able to avoid wondering, Is this really just the flu?

With reporting by Nancy Harbert/Albuquerque and Lisa H. Towle/Raleigh