 |
|
Home -- ENSO Cycle -- ENSO Effects -- Missions -- Data -- Tools -- Site Map |
|
Introduction -- South America -- East Africa -- Pakistan -- Philippines -- Local Links -- Web Links |
|
||||
Malaria
Introduction
Malaria parasites have man as the only vertebrate host and Anopheles mosquitoes as the vectors. At least 300,000,000 people are affected by malaria globally, and there are between 1 and 1.5 milion malaria deaths per year. The direct and indirect annual costs of malaria were estimated at $2 billion in 1997 by an official of the World Health Organization (WHO).
|
Countries with Endemic Malaria Areas |
Disease Vector |
Changed rainfall patterns (TOVS rain data) (TRMM TMI rain data) have been shown to have a strong effect on the transmission of malaria. The effects are stronger along the edges of endemic malaria regions, where malaria-transmitting mosquitoes have access to hosts already infected. The mosquitoes can easily spread into new territory, or have better reproductive success, under wet or dry conditions that are beneficial for a particular season or year.
Normally dry areas that receive abundant rainfall develop short-term puddles and marshes. Under drought conditions (Pathfinder NDVI data), rivers and streams in normally moist areas become strings of still-water pools. The common El Niño-La Niña events of drought followed by heavy rain contributes to increased incidence of malaria in dry regions. The vulnerable human population has increased in size due to poor-diet and lowered general immunity (when the rain sets in, humans can not grow crops and become better nourished faster than the mosquitoes can breed). A contributing factor is the decrease in the fish population that is the natural predator of mosquitoes (mosquitoes breed faster than fish). Both wet and dry conditions can favor mosquito reproduction, but the detailed response depends upon the ecological requirements of the local vector species.
Normally cool areas at higher elevations or latitudes, where mosquitoes are limited by freezing winter temperatures, may be warmed by extreme ENSO events. Normally warm areas may have shorter cool seasons and higher temperatures during warm seasons. Both conditions allow malaria-carrying mosquitoes to expand into formerly inhospitable regions.
The 1997-98 El Niño was predicted and monitored for effects. Studies involving previous El Niño events and malaria are retrospective studies. Disease impacts have only been monitored for this one El Niño; the next El Niño event will need to be predicted and the impacts studied before the findings can be fully embraced by the scientific community.
South America
Some countries in South America receive exceptional amounts of rainfall during an El Niño season; others receive less-than-normal rainfall. In the 1983 El Niño, wet Ecuador, Peru, and Bolivia suffered serious malaria epidemics. Dry Venezuela and Colombia had a 37-percent increase in malaria cases in the year, the 1997-98 El Niño, when the rains returned (La Niña event). Mosquito populations exploded in Brazil, and by the end of 1998, some small villages had malaria rates of 80 percent of the population.
East Africa
Sever malaria outbreaks have been recorded for the African country of Malawi. Eastern Africa receives above-normal rainfall from a warmed Indian Ocean during El Niño events; Malwai experienced increased rainfall at the end of 1997. The months from December to February are normally considered to be the dry season, but during the 1997-98 El Niño event these months were very wet (TOVS rain data). The observed precipitation was more than 5 to 10 times above normal. The vegetation growth was monitored by satellite sensors, which showed above-normal NDVI anomalies. The precipitation amounts in Malawi during 1988 correlates with the increasing death rate; health records are not sufficient to be able to attribute all of the increases in deaths to malaria.
Malaria is endemic to Kenya, but recent heavy rains caused in part by the 1997-98 El Niño have significantly increased the number of reported cases. A deadly strain of malaria has killed 143 people in northeastern Kenya during October to December 1997. In April to June 1999, a malaria outbreak in southwestern Kenya killed at least 260 people.
Pakistan
After excessive monsoon rainfall related to an El Niño, the Punjab region of Pakistan and nearby India suffered from malaria epidemics. The risk of malaria infection was 5 times greater during an El Niño. Malaria is now controlled (by DDT) in the Punjab, but is still a risk in more arid neighboring regions.
Philippines
In January and February 1998, malaria killed 135 people on a southern Philippine island and 31 on another island.
Disclaimer: NASA offers these suggested sites for additional information regarding malaria and 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.
Malaria Web Sites
