• Air out closed-up buildings, such as woodsheds, before entering in the spring.
El Niño Link
In 1993 a Hantavirus outbreak in the Four Corners region of the U.S. Southwest killed an estimated 20 people.
Yates, the University of New Mexico biologist, studied the outbreak and linked its occurrence with unseasonably wet weather triggered by the El Niño weather phenomenon.
El Niño is a periodic warming of Pacific Ocean waters near the Equator that can affect U.S. weather patterns, including heavier precipitation in the Southwest.
"Basically, two years after the original input of moisture into the environment, we have an explosion of rodents," Yates told a Pulse of the Planet radio program airing today.
(This news article and Pulse of the Planet are sponsored by a grant from the National Science Foundation.)
"[C]limate change or climate fluctuation … triggers a plant response, which triggers a rodent response, which triggers an outbreak of the virus in the rodent population, which then increases human risk for contracting the virus," he said.
A small El Niño is linked to the unseasonably wet winter of 2005, Yates notes. Many climate scientists predict there will be more frequent and more intense El Niños in the future. This may cause even more disease outbreaks, the biologist says.
Virus Tracking
Yates studies how viruses spread. In addition to weather patterns, a major facilitator is the loss of biodiversity.
His research in Panama, for example, shows that where the rain forest has been cleared for cattle pastures, rodent diversity is low and rates of Hantavirus infections are high.
Yates says that in species-rich communities, the chances for a virus to spread are more limited, because the chances for the virus to successfully find a host are limited.
For example, given an area where there are a hundred rodents drawn from ten different species, "90 percent of the virus particles are landing on the wrong species," he explained. "So it's a dead end. They can't be passed on."
He says that in a diverse community the virus quickly ceases to exist, because it is seldom successfully spread.
Disturbed environments such as a cleared rain forest, however, are favorable to only a few species and thus allow those particular species to experience population explosions. Any disease spread by those species is thus more likely to survive, Yates says.
In Panama and other tropical and sub-tropical regions of the world, the kinds of rodents that thrive in disturbed habitats tend to be carriers of Hantavirus, Yates notes.
"Not only are there more bad kinds of rodents, but there is a higher percent of those bad rodents that are infected, therefore human risk greatly increases," he said.
While Yates says he has not directly tested the hypothesis in the U.S. Southwest, he believes human-altered landscapes there may help spread Hantavirus.
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