Study Links El Nino to Deadly South American Disease

In a groundbreaking collaborative study, NASA climatologists and U.S. military health

specialists may have discovered a way to predict outbreaks of a deadly South American disease by observing sea surface temperature.

The researchers found that the worst outbreaks of Bartonellosis, an insect-borne disease highly fatal to humans, are closely related to the climate event El Ni–o. These outbreaks occur one to three months after the warming of the tropical eastern Pacific Ocean that is associated with El Ni–o. If confirmed, the findings could enable health workers to stave off future epidemics before they begin.

“We now have strong evidence that there is a relationship between climate and Bartonellosis,” said William K. Lau, head of the Climate Radiation Branch at the NASA/Goddard Space Flight Center. “It’s not proven yet, but we are now one step closer.”

The evidence could allow health officials to predict and combat epidemics far more effectively.

“It appears that the disease comes in weather-related cycles,” said Larry Laughlin, Chairman of the Department of Preventive Medicine at the Uniformed Services University of Health Sciences (USUHS). “If we can prove it, local health officials will be able to take preventive action when they know a ‘bad year’ is coming. This is a critical factor in developing countries where healthcare resources are limited.”

The findings will be presented on January 17 at the American Meteorological Society Meeting in Orlando, Fla.

NASA earth scientists teamed with Laughlin’s group at USUHS to study Bartonellosis, a disease that is characterized by life-threatening anemia. There is also a chronic form of the disease that manifests itself in blood-filled, wart-like skin lesions. Bartonellosis appears to be spreading from the mountain valleys of Peru into other regions of Andean South America.

“We think the disease is transmitted to humans by the bite of sand flies, much as malaria is by mosquitoes,” Laughlin said. “Since the acute disease is fatal in 40 percent of cases if left untreated, it is important to identify the factors that encourage its spread.”

The group studied two regions of Peru known as Caraz and Cusco. While the mountainous region of Caraz has a long history of Bartonellosis outbreaks, it was unknown in the more southern Cusco until recently. The deadliest recent outbreak was during the South American summer and fall months of December 1997 to May 1998. Since the 1997-98 season was also the strongest El Ni–o event of the 20th century, the scientists compared sand fly breeding observations with weather data from NASA’s Tropical Rainfall Measuring Mission (TRMM) satellite.

“We noticed that extremely high numbers of sand flies were collected during the 1997-98 season,” Lau said. “That season had double the average number of Bartonellosis cases. The disease also spread to the southern part of the country, where it had not been seen before. The data lead us to believe that El Ni–o was the dominant factor in the epidemic.”

Since indications of El Ni–o can be seen by satellites months before it affects the sand fly breeding season in South America, the scientists believe they can serve as an advance warning of an approaching epidemic year. But further study is necessary to strengthen the connection’s validity.

“We were only able to use data between 1994 and 1999,” Lau said. “There was only one El Ni–o event during that period, and that’s not enough to establish a conclusive link. But we now think that, with further study, predictions of epidemics will be possible in the future.”

The study marks the first time that researchers from the two widely divergent disciplines of climatology and disease prevention have collaborated.

“This is a prime example of how two organizations came together and did something that wouldn’t have been possible otherwise,” Laughlin said. “Had we each been left to our own devices, NASA might still be focusing on predicting El Ni–o but not paying attention to disease, while we might be spraying the same amount of insecticide every year with poor effect on disease control. As a result of looking outside our own disciplines, though, we can now help more people while saving money and effort.”

This research is supported by NASA’s Earth Observing System/ Interdisciplinary Science investigation on hydrological processes and climate, and the Global Modeling and Analysis Program of NASA, Earth Science Enterprise and a NOAA grant.

For more information, see: http://www.gsfc.nasa.gov/topstory/20020117bartonellosis.html

NOTE: This presentation, Session 6.6, will be given at the 82nd Annual meeting of the American Meteorological Society, at the Orange County Convention Center on Thursday, January 17 at 9:30am.