When young, otherwise healthy people in the remote Four Corners area of Arizona and New Mexico began dying of a mysterious, acute respiratory disease in the spring of 1993, scientists wondered at the cause.

Tests of the victims’ blood yielded surprising results: the people had become infected with a previously undetected kind of hantavirus.  Named for the Hantaan River in Korea, hantaviruses were known to spread from rodents to humans in Asia and Europe, but until the Four Corners outbreak, the microbes had only been seen outside of the United States.

Massive rainfall associated with El Niño boosts plant productivity. Feasting on the more abundant plant matter, the rodent population grows. Increased contact with rodents and their waste puts more humans at risk for exposure to hantavirus. Credit: Zina Deretsky, National Science Foundation

For answers as to how the virus spread in the Four Corners, the U.S. Centers for Disease Control turned to scientists Robert Parmenter of the Sevilleta (SEV) Long-Term Ecological Research (LTER) site in New Mexico, and Terry Yates of the University of New Mexico.  Their research at the LTER site revealed that the hantavirus outbreak could be blamed on El Niño, a periodic pattern of change in the global circulation of oceans and atmosphere.  Massive rains associated with the 1991-1992 El Niño had substantially boosted plant productivity after several years of drought. A banner year for plants was followed by a banner year for rodents. More mice meant that more humans stood a greater chance of exposure to infected rodents as people moved among barns and did spring cleaning of cabins and trailers.

The deadly hantavirus wasn’t new to New Mexico.  The virus had been in the rodents all along.  It was the change in climate conditions that triggered the fatal outbreak in humans.  Such knowledge likely saved lives in 1998, when another active El Niño prompted health authorities to warn residents in the American Southwest to use caution when entering areas favored by mice.

Further information about the SEV LTER is available at http://www.lternet.edu/sites/sev/

General information about the LTER Network, including links to each of the LTER sites, is available at http://www.lternet.edu