Steve Quayle News Alerts

December 10, 2002
By Robert Cooke, STAFF WRITER

In a scenario similar to dominoes toppling, the first one is El Niño, the climate phenomenon that erupts in the Pacific. And the final domino to drop, thousands of miles away, is diagnosis of a dreadful disease, hantavirus.

The connection - the other dominoes - includes more moisture in the arid U.S. Southwest, greener grass and shrubbery, more nuts and seeds to eat, a population explosion among mice and other rodents, and sudden spread of the virus. People then get the disease. This is what happened in 1993, again in 1999, and is about to happen again as another El Niño gains momentum.

This newly discovered chain of cause and effect - disease resulting from a faraway change in climate - has come to light even as the world gets edgier than ever about bioterrorism, global warming and emerging diseases. The hantavirus outbreaks were natural events, first seen in 1993 when 10 people died. The next outbreak started in 1998, marked by seven cases, nine in 1999 and 13 in 2000. Deaths had become less common - only 40 percent of cases - because doctors had learned what to look for, and what to do earlier in the course of disease. Now, the scenario seems about to repeat.

'There is an El Niño well under way," said climate specialist Kevin Trenberth, director of the climate analysis section of the National Center for Atmospheric Research, in Boulder, Colo. "In the past two or three months it's been building up and making its presence felt."

He said the climate change is "associated with the stormier weather we've seen across North America in October and November; the cool weather and snow in the mountains."

Among El Niño events, however, it's not a whopper, Trenberth said. "It looks like a moderate El Niño, not as big" as the last one. "But there will be a pattern to the weather, a more active storm track across the south, from southern California through Florida." To the north, he added, the weather may be drier than usual during the 18-month El Niño episode.

The sudden burst of hantavirus infections in 1993 came as a major surprise. The disease arrived suddenly - it had never been seen outside Europe and Asia - killing 10 people in and around New Mexico in May and June. The cause was initially a mystery, and no one could say for sure if it was a virus and, if so, where it came from and how it was being spread.

People throughout the Four Corners region of the Southwest were scared, and it didn't help when publications such as Scientific American suggested the disease may have been the result of accidental release of a military biowarfare agent. There was also speculation it was a bioterrorism attack, since infection seemed so deadly.

"There was no cure, no successful medication or treatment, and the disease agent was completely unknown. For the first few weeks, the mortality rate was 70 percent," according to a report by a team of 16 disease detectives.

Now, according to the team's report in BioScience magazine, the ecology and the evolutionary history of the two disease outbreaks have been sorted out. And, one team member noted, the next disease outbreak may come within a year.

These El Niño climate episodes are an increasingly well-understood phenomenon, occurring every four to seven years. What has been less clear is their downstream ecological effect, especially the link to diseases.

El Niños originate with an increase in Pacific Ocean surface temperatures in a zone stretching from Peru west along the equator toward Asia. El Niños vary in strength, timing and length from one event to the next, but weather experts are getting better at predicting their severity. The term El Niño means "the child," since El Niños usually become obvious to South Americans in December.

El Niño events alter the weather by forcing storms to follow different tracks. They also tend to decapitate Atlantic hurricanes before they can form near Africa, and they alter global weather patterns to bring flooding to parts of South America, and droughts to northeast Australia.

Among the things El Niño also does is send extra moisture into normally arid regions, including the Four Corners area where the borders of Arizona, Utah, Colorado and New Mexico meet. It was in such areas that the hantavirus outbreaks erupted.

Researchers say the El Niño-spawned hantavirus outbreaks offer a clear warning that more diseases are out there - diseases that scientists aren't yet aware of. Different infectious microbes are certainly lurking among bugs and animals; in fact, about 62 percent of the known human infections are zoonotic, or transmitted to people from animals, or through carriers such as mosquitoes, fleas and ticks.

"Before this [1993] outbreak, we didn't know of any hantaviruses anywhere in the New World," said biologist and pathologist Terry Yates. "And if that's how much we knew about the world's second-most-deadly virus, what don't we know about the others?"

The world's most deadly known virus, he added, is Africa's ebola virus.

As a result of what's been learned from the two outbreaks - the first in 1993, the second spanning 1998 to 2000 - dozens of other hantaviruses have been identified in Western Hemisphere animals. Because researchers now know what to look for, some hantaviruses were discovered even in New York (one disease case on Long Island), Pennsylvania and Florida. Further, in both North and South America, hantaviruses have been found in various species of mice and rats, and are suspected to be in similar rodents, such as voles and lemmings.

Yates, vice president for research at the University of New Mexico, is the lead author on the study. Each outbreak began roughly a year after an El Niño event dumped extra moisture in the southwestern United States.

"If this El Niño is similar to the two previous ones in the 1990s," Yates said, "then we should see another cascade: a response in the plant community [more food], an increased rodent response [more mice] and an increase in disease in humans."

The increase in mouse population density is an important factor, Yates explained, because crowding more animals into a given area allows the disease to spread easily and widely, enhancing chances that humans will come into contact with the virus.

Yates said hantavirus infections in humans seem to result from inhalation of contaminated dust particles. Viruses get into the dust via rodent excreta, meaning the urine and feces they leave behind. Unlike ebola, which causes severe hemorrhaging, the New Mexico sin nombre (without name) hantavirus causes lung infections, with early symptoms very much like influenza's. "That is why we missed it" before 1993, Yates said.

After the initial symptoms, the next step is often deadly. The research team wrote that many victims' conditions "suddenly and rapidly deteriorated as their lungs filled with fluids; death usually occurred within hours of the onset of this crisis period."

Within weeks of the first outbreak, experts from state health departments and the U.S. Centers for Disease Control and Prevention had identified the cause, and an intensive sampling campaign of field rodents ensued in New Mexico and Arizona.

Soon, the researchers said, the CDC's team also "identified the viral reservoir host as a common and widely distributed rodent, the deer mouse." At the same time, members of medical staffs began devising treatments that could maintain and stabilize some patients through the crisis period, improving the survival rate.

For scientists, the lesson is that "ecological forecasting is possible if we have sufficient information and resources," Yates said. Efforts are under way to mount a project to identify all living species on Earth to help in such battles against disease. This so-called "Tree of Life" project will include all the animals, birds, fish, insects, plants, fungi, bacteria, viruses - everything that lives.

The usefulness of a Tree of Life diagram was made obvious by the hantavirus outbreaks: "Our knowledge of the Tree of Life for these rodents is what allowed us to predict where we should find new hantaviruses in nature," Yates explained. The recently identified hantavirus family members now number more than two dozen among various kinds of rodents.

Experts expect that such Tree of Life data will become especially vital as the global atmosphere gets warmer because of greenhouse gases accumulating in the air. Climate will probably be changing, and weather patterns - meaning the extremes of storms, floods and droughts - will change along with it. So there will be danger from new diseases, or from known diseases moving into new ecological areas. Malaria, for example, could make inroads into parts of the United States, even as West Nile virus has. Malaria's spread would be into wet, warm parts of the nation via mosquitoes that thrive in such conditions.

For the present, doctors in the Southwest can be prepared to treat sick people sooner, and perhaps more effectively. Even in the 1993 outbreak, the mortality rate was reduced from an initial 70 percent down to 40 percent.

If something akin to the surprise hantavirus episode were to erupt today, the national response might also be far different. In the wake of the recent anthrax attack-by-mail episode, a new unidentified outbreak of any kind would be suspected as a possible bioterrorism attack, and vast resources likely would be mustered quickly.

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