Links between climate, malaria, and wetlands in the Amazon Basin.Global models of malaria can be used to forecast the impact of climate change on malaria, a highly climate-sensitive disease that causes >1 million deaths worldwide each year, mostly in children. However, a limitation of these models is the application of a uniform malaria-precipitation relationship to geographically diverse regions (1-3). Moreover, the Millennium Ecosystem Assessment The Millennium Ecosystem Assessment (MA) is a research program that focuses on ecosystem changes over the course of decades, and projecting those changes into the future. It was launched in 2001 with support from the United Nations by the UN Secretary-General Kofi Annan. has recognized a lack of knowledge about climate-sensitive diseases such as malaria and has called for a "more systematic inventory, by region and country, of current and likely population health impacts of ecosystem change" (4). Understanding malaria-precipitation relationships at regional levels will enhance predictability of ecosystem or climate change impact on population health.
Precipitation and surface hydrology hydrology, study of water and its properties, including its distribution and movement in and through the land areas of the earth. The hydrologic cycle consists of the passage of water from the oceans into the atmosphere by evaporation and transpiration (or are key factors in determining the abundance of Anopheles Anopheles: see mosquito. mosquito vectors for malaria. Mosquitoes require pools of water to complete their life cycle, and malaria models have estimated changing transmission by setting minimum levels of precipitation below which mosquito populations are (theoretically) suppressed. However, using a uniform hydrologic threshold for malaria does not capture critical characteristics of landscape, soil, and rainfall (i.e., intensity, frequency), all known contributors to the abundance, persistence, and spatial distribution of mosquito habitats.
In the Amazon Basin, the predominant malaria vector is Anopheles darlingi. Short longitudinal studies longitudinal studies,
n.pl the epidemiologic studies that record data from a respresentative sample at repeated intervals over an extended span of time rather than at a single or limited number over a short period. show that human-landing catches of An. darlingi, which breeds along the edges and in debris of clear, partially sunlit sun·lit
Illuminated by the sun.
Adj. 1. sunlit - lighted by sunlight; "the sunlit slopes of the canyon"; "violet valleys and the sunstruck ridges"- Wallace Stegner
sunstruck pools, are closely associated with local malaria rates (5,6). These observations establish that biting rates are elevated in regions of elevated malaria risk. Likewise, biting rates correlate with abundance of larvae Larvae, in Roman religion
Larvae: see lemures. and larval larval
1. pertaining to larvae.
see cutaneous and visceral larva migrans. habitats and proximity of humans to larval habitats (7,8).
Local observations demonstrate the existence of different seasonal patterns for malaria. In a 3-year study in Roraima, 8 municipalities showed increased risk for malaria during the middle of the dry season or shortly after the wet season (9). Other literature on seasonal patterns is limited to local and short (<3 years) longitudinal studies that lack statistical analysis. Although different seasonal patterns emerge in graphs, the collage of different data sources makes formulating a cohesive picture of these patterns in the Amazon region difficult.
At the regional level, interannual climatologic cycles provide insight into low-frequency malaria patterns. In Columbia, El Nino events (caused by warming sea surface temperatures in the central tropical Pacific) are associated with warmer temperatures, higher dew points, and less precipitation and river discharge. These climate changes have been associated with increases in malaria during the second half of El Nino years and during the following year (10). Similarly, malaria incidence has increased during the year after an El Nino event in Venezuela and Guyana (11).
Using monthly reports of malaria and precipitation from across the Brazilian Amazon Basin, we demonstrate that malaria incidence and precipitation patterns vary throughout this large region and are influenced by the extent of wetlands.
We used monthly reports of slide-confirmed malaria and annual census-based population data from 434 counties (municipios) in the Brazilian Amazon region for 1996-1999, during which no coordinated national malaria interventions occurred (12). To study the relationship of reported malaria cases to climate, we used monthly precipitation and temperature from the CRU TS 2.1 gridded climate data set for selected states (13) (Figure 1). To consider how the precipitation-malaria relationship depends on surface water conditions, including the extent of open water and wetlands, we used 100 m x 100 m maps from the JERS-1 Synthetic Aperture Radar Synthetic aperture radar (SAR)
Radar, airborne or satellite-borne, that uses special signal processing to produce high-resolution images of the surface of the Earth (or another object) while traversing a considerable flight path. satellite and calculated the percentage of maximum inundatable open water and wetland coverage for each county (Figure 2, panel A) (14). In this region, monthly temperatures were between 24.6[degrees]C and 29.4[degrees]C (well within the range for optimal malaria transmission) for 95% of the observations (18,416 of 19,364) included in the analysis (temperature relationships not shown).
[FIGURE 1 OMITTED]
Evaluation of seasonal patterns requires comparability of the models across regions. If the lag and the rainfall coefficient vary across regions, meaningful geographic comparisons would be difficult to achieve because neither the lag nor coefficient have consistent meanings across models. To interpret results, either the coefficient must be fixed and the lags varied (difficult to do) or the lags must be fixed and the coefficients varied (relatively easy to do). The aim is to describe the variable patterns of malaria incidence and precipitation, not create a highly predictive model. We chose to fix the lag and vary the coefficients.
To assess the association between malaria incidence and precipitation data, we estimated the rate ratio of malaria incidence associated with 1 SD-increase in monthly precipitation ([approximately equal to]14 cm) for each county by using the following Poisson regression model, which includes a flexible temporal trend represented as a natural cubic spline In computer graphics, a smooth curve that runs through a series of given points. The term is often used to refer to any curve, because long before computers, a spline was a flat, pliable strip of wood or metal that was bent into a desired shape for drawing curves on paper. See Bezier and B-spline. with 6 degrees of freedom (Figure 2, panel B):
[malaria.sub.it] [approximately equal to] Poisson([[mu].sub.it]) log [[mu].sub.it] = log [pop.sub.it] + [[alpha].sub.i] + [[beta].sub.i][precip.sub.it] + [f.sub.i](t) [[beta].sub.i] [approximately equal to] Normal(g([lat.sub.i], [lon.sub.i]), [[sigma].sup.2])
The (estimated) regression coefficients from the county-specific models were then modeled as a spatially smooth surface, a thin-plate spline. Degrees of freedom for the thin-plate spline were selected using generalized crossvalidation (Figure 2, panel C).
The relationships between precipitation and malaria incidence in the Amazon Basin are spatially varied and change signs, depending on the region. Positive correlations between monthly precipitation and malaria incidence (rate ratios >1) occur in the upland regions of the southwest and central Amazon Basin, whereas negative correlations between precipitation and incidence (rate ratios <1) occur in the north, largely along the main waterways of the Amazon River and the major wetland regions of the Basin (Figure 2). For a [approximately equal to]14-cm increase in monthly rainfall, the malaria rate can double in the upland area, yet decrease by up to 80% along the main Amazon channel. The p values of the precipitation coefficient are 0.0002-0.0009 along the main waterways and 0.004-0.10 in uplands areas.
We hypothesize hy·poth·e·size
v. hy·poth·e·sized, hy·poth·e·siz·ing, hy·poth·e·siz·es
To assert as a hypothesis.
To form a hypothesis. that this reversal of the malaria-precipitation relationship from positive to negative is related to the extent of open water and wetlands in the Basin. Mosquito habitats in wetlands or along large rivers may wash out or become too deep during months with high precipitation, but in areas with fewer wetlands, mosquito habitats are limited by precipitation.
To test this hypothesis, we compared the malaria- precipitation association for 338 counties that reported [greater than or equal to]80 cases of malaria over the 48 months against the estimated percentage of open water and wetland cover for each county (Figure 2, panel D). As expected, the precipitation-linked risk for malaria fell as the percentage of wetland in each county increased, but the risk for malaria varied in counties with low percentages of wetlands. The central-east region had the lowest level of malaria incidence, which may explain why this region also lacked a malaria-precipitation relationship.
Explanations similar to our wetlands hypothesis have been reported. Studies have proposed that flooding created new pools of water suitable for mosquito larvae as the water levels slowly receded from alluvial forests along the Rio Branco River in Roraima and the Maroni River on the frontiers of Suriname and French Guiana (6,15). Our results suggest that monthly precipitation along the Amazon Basin can have both strong positive and negative associations with malaria incidence.
[FIGURE 2 OMITTED]
Further research is needed to address the limitations of our study, including its short time frame and the crude countywide approximation of percentage wetlands as an exposure. The quality and reliability of the health data were concerns, but we verified that the distribution of null reporting was unbiased temporally and spatially. Also, our study did not quantify increasing malaria incidence in response to increasing or decreasing precipitation or the impact of lag factors. Instead, we focused on the seasonality of these patterns until longer data series of malaria incidence and climate data are available.
Our evidence suggests that precipitation drives malaria risk in the Amazon Basin, but the relationship varies in the uplands (more precipitation, more/less malaria) and is negative in areas dominated by wetlands and large rivers (more precipitation, less malaria). Our findings show the need to account for local landscape characteristics, especially the extent of wetlands and open water, in regional to global projections of the effects of climate change on malaria. Better understanding the impact of climate and landscape on malaria will improve our ability to assess health risks.
We thank Enrique Loyola for assistance with the malaria data, which originated from the Brazilian Ministry of Health.
This study was supported by the National Aeronautics and Space Administration National Aeronautics and Space Administration (NASA), civilian agency of the U.S. federal government with the mission of conducting research and developing operational programs in the areas of space exploration, artificial satellites (see satellite, artificial), LBA-ECO program and a National Science Foundation (NSF NSF - National Science Foundation OISE-0623583)-Franco-American Cultural Exchange exchange grant.
Ms Olson is working toward a joint PhD from the University of Wisconsin-Madison “University of Wisconsin” redirects here. For other uses, see University of Wisconsin (disambiguation).
A public, land-grant institution, UW-Madison offers a wide spectrum of liberal arts studies, professional programs, and student activities. . Her course of study combines a degree in population health from the School of Medicine and Population Health and a degree in environment and resources from the Nelson Institute. Her research addresses regional landscape and climate links in the ecology of vector-borne infectious diseases.
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A protozoan that causes falciparum malaria. transmission: implications for malaria control and elimination worldwide. PLoS Med. 2008;5:e38. DOI: 10.1371/journal.pmed.0050038
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(7.) Vittor AY, Gilman RH, Tielsch J, Glass G, Shields T, Lozano WS, et al. The effect of deforestation deforestation
Process of clearing forests. Rates of deforestation are particularly high in the tropics, where the poor quality of the soil has led to the practice of routine clear-cutting to make new soil available for agricultural use. on the human-biting rate of Anopheles darlingi, the primary vector of falciparum malaria fal·cip·a·rum malaria
Malaria caused by Plasmodium falciparum and characterized by severe malarial paroxysms that recur about every 48 hours and often by acute cerebral, renal, or gastrointestinal manifestations. in the Peruvian Amazon. Am J Trop Med Hyg. 2006;74:3-11.
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(11.) Gagnon AS, Smoyer-Tomic KE, Bush AB. The El Nino Southern Oscillation Noun 1. El Nino southern oscillation - a more intense El Nino that occurs every few years when the welling up of cold nutrient-rich water does not occur; kills plankton and fish and affects weather patterns and malaria epidemics in South America. Int J Biometeorol. 2002;46:81-9. DOI: 10.1007/s00484-001-0119-6
(12.) Pan American Health Organization The Pan American Health Organization (PAHO) is an international public health agency with 100 years of experience in working to improve health and living standards of the countries of the Americas. It serves as the specialized organization for health of the Inter-American System. . PAHO PAHO Pan American Health Organization (WHO) Roll Back Malaria Initiative in the Rainforest Region of South America. Cartagena. Washington: The Organization; 2000.
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Sarah H. Olson, Ronald Gangnon, Eric Elguero, Laurent Durieux, Jean-Francois Guegan, Jonathan A. Foley, and Jonathan A. Patz
Address for correspondence: Sarah H. Olson, Center for Sustainability and the Global Environment, University of Wisconsin, 1710 University Ave, Madison, WI 53726, USA; email: firstname.lastname@example.org
Author affiliations: University of Wisconsin, Madison, Wisconsin, USA (S.H. Olson, R. Gangnon, J.A. Foley, J.A. Patz); Montpellier University, Montpellier, France (E. Elguero, J.-F. Guegan); Institut de Recherche re·cher·ché
1. Uncommon; rare.
2. Exquisite; choice.
3. Overrefined; forced.
4. Pretentious; overblown. pour le Developpement, Lago Sul, Brazil (L. Durieux); and French School of Public Health, Paris, France (J.-F. Guegan)
Kaposi [kah'po-she, kap'o-se] sarcoma sarcoma (särkō`mə), highly malignant tumor arising in connective- and muscle-cell tissue. It is the result of oncogenes (the cancer causing genes of some viruses) and proto-oncogenes (cancer causing genes in human cells).
First described by dermatologist Moritz Kaposi (1837-1902) at the University of Vienna History
The University was founded on March 12, 1365 by Duke Rudolph IV and his brothers Albert III and Leopold III, hence the additional name "Alma Mater Rudolphina". After the Charles University in Prague, the University of Vienna is the second oldest university in Central in 1872. Dr Kaposi's last name was originally Kohn, but to distinguish himself from other physicians of the same name, he chose a new name in honor of the Kapos River, near his birthplace, Kaposvar, Hungary. The condition he described, Kaposi sarcoma Kaposi sarcoma
Usually lethal cancer appearing as red-purple or blue-brown spots on the skin and other organs. It has been linked to one of the herpes viruses, and there is considerable debate about how it should be classified. , is a malignant tumor malignant tumor
A tumor that invades surrounding tissues, is usually capable of producing metastases, may recur after attempted removal, and is likely to cause death unless adequately treated. of the lymphatic lymphatic /lym·phat·ic/ (lim-fat´ik)
1. pertaining to lymph or to a lymphatic vessel.
2. a lymphatic vessel.
adj. endothelium endothelium /en·do·the·li·um/ (-the´le-um) pl. endothe´lia the layer of epithelial cells that lines the cavities of the heart, the serous cavities, and the lumina of the blood and lymph vessels. , characterized by bluish-red cutaneous cutaneous /cu·ta·ne·ous/ (ku-ta´ne-us) pertaining to the skin.
Of, relating to, or affecting the skin.
Pertaining to the skin. nodules Nodules
A small mass of tissue in the form of a protuberance or a knot that is solid and can be detected by touch.
Mentioned in: Leprosy . Human herpesvirus herpesvirus, any of the family (Herpesviridae) of common DNA-containing viruses, many of which are associated with human disease. See cytomegalovirus; Epstein-Barr virus; herpes simplex; herpes zoster. 8 has been implicated im·pli·cate
tr.v. im·pli·cat·ed, im·pli·cat·ing, im·pli·cates
1. To involve or connect intimately or incriminatingly: evidence that implicates others in the plot.
2. in its etiology.
Source: Dorland's illustrated medical dictionary, 31st ed. Philadelphia: Saunders; 2007; http://www.hemoctoday.com/article.aspx?rid=31545