 |
|
Home -- ENSO Cycle -- ENSO Effects -- Missions -- Data -- Tools -- Site Map |
|
Introduction -- Local Links -- Web Links |
|
||||
Diseases
Introduction
Preliminary results from ongoing research indicates that changing environmental conditions has led to changes in how and where plants, animals, and people contact diseases. Floods wash sewage and fertilizer into water supplies. Enriched and warmed lake and estuarine waters often support blooms of harmful algae that contaminate fish and shellfish, and support the growth of pathogens harmful to people and animals. A change in the environment changes the numbers or locations of not only the disease agent but also the agent's primary host or vector, due to mechanisms such as increased overwintering success and/or increased host thermal stress in the summer (Science vol. 296, 21 June 2002, pp. 2158-2162). Warmer-than-normal conditions allow both pathogens and vectors to invade new regions. Usually these research efforts have spanned only one El Niño event, or are retrospective investigations; additional research spanning a new El Niño is needed to confirm the preliminary findings.
|
|
Disease Vectors |
|
Details of the relationship of disease with ENSO events vary (e.g., in lag time) depending upon the disease vector and its ecological requirements, the intensity and timing of the ENSO event, and changed weather patterns. Both warm and cold events may help the disease organism and its vector. During the El Niño year 1997-98, simple childhood diarrhea cases brought to a clinic in Lima, Peru, were twice as many as expected. Cholera may infect the Peruvian population during an El Niño event where a phytoplankton bloom (SeaWiFS chlorophyll data) is the vector. In Ecuador, the number of cholera cases during the 1991-92 event was 17 times those of 1997-98. The hauntavirus of the Southwest United States claims more victims after an El Niño winter because increased rainfall (TOVS rain data) (TRMM TMI rain data) results in more vegetation that supports rodents. In Central America, in the aftermath of Hurricane Mitch (October 1998), Honduras reported thousands of cases of cholera, malaria, and dengue fever. No two ENSO events are alike, and thus no two outbreaks of ENSO-related diseases are alike.
The blood-sucking female mosquito is a common vector for diseases. Rainfall (TOVS rain data) (TRMM TMI rain data), unless flooding washes out breeding grounds, provides both breeding sites for mosquitoes and suitably humid living conditions for the adults. A correlation with increased rainfall may be true for both Rift Valley Fever in East Africa and Ebola hemorrhagic fever in equatorial Africa. However, drought is a contributing factor in increased incidence of malaria in Africa, because the general immunity of the local human population is reduced (the size of the vulnerable population has increased) and the change in the ecology decreases the fish population that is the natural predator of mosquitoes; mosquitoes respond faster than fish to new rain. The mosquitoes that spread West Nile virus may survive better during a mild La Niña winter to infect birds (and people) along migration paths on the U.S. eastern seaboard. Similar mosquito survival appears to result in California outbreaks of St. Louis encephalitis during hot and dry La Niña summers. Increased mosquito abundance during cool and wet El Niño years due to the increase of suitable mosquito habitat appears to result in increased infections of Western equine encephalomyelitis. Cyclic ENSO-related changes in temperature and rainfall appear to influence the incidence of many mosquito-delivered diseases.
Climatic changes, both in themselves (e.g., sea surface temperature (Pathfinder SST data)) and in the response of the land cover (e.g., vegetation index (Pathfinder NDVI data)), can be detected and monitored in order to derive the presence and activity of disease-causing organisms and diseased people or livestock.
Jump to 'Disease' List of Web Sites
Disclaimer: NASA offers these suggested sites for additional information regarding effects of El Niño and La Niña teleconnection events. Web access is required to reach these sites. Link existence and contents are not under the control of the EOSDIS Science Operations Office.
Diseases Web Sites
