BALTIMORE, Dec. 2 (UPI) -- Using new data analyses, satellite remote sensing could help identify potential areas of high risk for often-fatal outbreaks of hantavirus, scientists reported Monday.
"We're almost at the stage of making forecasts about disease risk," lead researcher Gregory Glass, a disease ecologist at Johns Hopkins Bloomberg School of Public Health, told United Press International. "For the first time, we have the potential of actually anticipating a problem before it happens."
As reported in the Dec. 2 online version of the Proceedings of the National Academy of Sciences, Glass and colleagues analyzed images taken by the U.S. Earth-observing satellite Landsat 5 of the southwestern United States in 1997 and 1998. That year the Earth experienced an unusually severe El Niño -- a warming of the ocean surface off the western coast of South America named after the Christ child, because it often begins around Christmas.
El Niño alters storm patterns globally, creating unusual weather patterns. The southwestern United States, for instance, was wetter than normal, Glass said.
Areas identified by satellite imagery as high risk for hantavirus had increased deer mouse populations beginning in 1998, he explained, based on results from mousetraps scattered throughout the wilderness. In 1999, the United States saw about a dozen new cases of hantavirus infections, Glass added.
"We found that at the beginning of the El Niño, when we just came out of a dry period, rodent populations were quite low and infection levels in those rodents were quite low," Glass said. "By the time the El Niño had finished, in the high risk areas the rodent populations just went through the roof, and the infection levels reached the point where almost a third of the mice were infected."
Previously to assess the risk hantavirus poses, scientists had to go into the field and sample mouse populations over hundreds of sites -- a time-consuming and labor-intensive effort. In contrast, the new satellite analysis "lets you survey an area of 100,000 square kilometers," Glass said.
The 1997 and 1998 findings have revealed the El Niño of those years that apparently triggered heavy monsoons and dengue fever outbreaks in Asia also might have started a chain reaction in the world's food webs that ultimately led to isolated outbreaks of hantavirus in the United States in 1999.
"This doesn't mean every time you have an El Niño, you're going to get large outbreaks. But it might set the stage, making the environment ripe for infection," Glass said.
Hantaviruses is a deadly microbe carried by rodents. When it first struck in 1993, the germ now simply known as Sin Nombre or "nameless" hantavirus killed half the young Native Americans it infected in the "Four Corners" area, where New Mexico, Arizona, Colorado and Utah meet. Since then, medical scientists have found the hantavirus in more than half of the U.S. states and in South America.
Sin Nombre virus attacks the lungs and appears to spread primarily through the deer mouse. Exposure to infected rodents or their excrement can lead to symptoms such as fever and muscle aches one to five weeks later, and immediate intensive care is then essential, according to officials at the Centers for Disease Control and Prevention in Atlanta.
Scientists had speculated changes to environmental factors such as soil moisture and types of vegetation could increase the risk of hantavirus. For instance, increased rainfall leads to more grass, "providing food for insects, which provides food for rodents, causing their populations to grow, and as they grow, you have a lot more transmission of virus among rodents that ultimately impacts humans," Glass explained.
The researchers still have not pinpointed the exact environmental factors that cause hantavirus levels to rise. Glass said he is working on applying this program in Chile, which has had even more cases of hantavirus infections than in the United States.
"These results are very promising, and it will be important to know whether these results can be repeated," said infectious disease specialist Gregory Mertz of the University of New Mexico in Albuquerque, a collaborator with Glass on the separate Chile project. "The situation will likely be different and equally complex in other parts of the world with different types of climate and vegetation, a different hantavirus, different rodent hosts, and different patterns of human habitation. The fact that this pattern did emerge here means we may be able to find something equally valuable in other situations."
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(Reported by Charles Choi, UPI Science News, in New York)
