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Hantavirus Pulmonary Syndrome (HPS)
Introduction
During an El Niño or a La Niña season, normally dry areas often receive excessive rainfall (TOVS rain data) (TRMM TMI rain data). The increased moisture permits explosive growth of plants (Pathfinder NDVI data) that directly provide food for grasshoppers and indirectly for rodents (which eat grasshopers and seeds. The increased "carrying capacity" of the land fosters an increase in rodents. Small animals respond better and faster than their predators (e.g., owls, eagles, hawks, canines, and snakes) to an increase in the supply of food, but the increase in numbers of rodents may outstrip the food supply. There is evidence that the Hantavirus infects humans after the wet phase of either an El Niño or a La Niña event when a temporary surplus of food followed by a lack of food brings more rodents into greater contact with people.
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Distribution of Deermouse and HPS Cases |
Deermice and some other rodents are infected with and transmit the Hantavirus. |
U.S. Four Corners
Identified in the United States in 1993 (New Mexico and Nevada), and retrospectively diagnosed for an incident in 1987 (Utah), HPS is a severe cardiopulmonary illness (40 to 46 percent case fatality rate). The initial outbreak took place after El Niño conditions of unusually high precipitation and during La Niña conditions (a wet and mild winter followed by a summer drought). In 1 year, the area's deer mice reproduced so rapidly that there were 10 times more mice than in the year before. Rodent populations form a reservoir for the hantavirus (a.k.a., No Name or Sin Nombre virus). In most cases, it appears that the people infected lived in houses or trailers with evident rodent infestation. Improved habitat quality (vegetation growth) resulting from above-average rainfall in normally dry regions increases the population of rodents, excreta, or contaminated dust into contact with humans.
During the 1997-98 El Niño, rodent populations grew dramatically in January and February of 1998, followed by a 3-year-long increase in the cases of HPS. Scientists from the University of New Mexico reported they have seen 14 cases between January and August 1998. In the states of Arizona, Colorado, and New Mexico, at least eight cases were confirmed during the 5-month period from January to May of 1999. The prevalence of antibodies for hantavirus in rodents dramatically increased between the spring of 1998 and 1999.
Central and South America
Cases of hantavirus infection,
or of the occurrence of similar non-infecting viruses, have been reported,
and often confirmed, from a variety of countries in South and Central America:
Reports indicate that each outbreak is connected with climatic and ecological events resulting in local increases of rodent populations. The outbreak in Chile is connected with high rodent numbers after a mild winter and the flowering of a species of bamboo. The outbreak in Panama followed an increase in rodents associated with increased rainfall and flooding during the fall and winter of 1999. However, the outbreak in Argentina does not appear to be connected with rodent infections, since the rodent population was low, but rather with person-to-person infection.
Disclaimer: NASA offers these suggested sites for additional information regarding effects of El Niño and La Niña events. Web access is required to reach these sites. Link existence and contents are not under the control of the EOSDIS Science Operations Office.
Hantavirus Web Sites
