CLIMATE CHANGE AND DISEASE

Science, Technology, and Environmental Policy (STEP) Program
Woodrow Wilson School of Public and International Affairs
Princeton University

Tania Simoncelli
M.S. student

Energy and Resources Group
University of California, Berkeley

Climate-Land use-Health-Population Interactions in Africa: Comparisons of Kenya and Mali

The aim of this project is to further the understanding of the impact of climate variability on human health from an ecological systems perspective. We will identify the causal relationships and interactions between climate events, regional ecology (including mosquito populations), and human behavior - including migration patterns, land use change, and infectious disease transmission. We will also examine governmental and non-governmental responses to these interactions and to disease incidence. Investigating these interactions in one region risks focusing on a set of interactions that are very location-specific. The interaction between agricultural production, migrations, and migration-related health status changes needs to be systematically studied in zones with different climate variability and climate adaptations if we are to develop appropriate early warning systems and other mechanisms to facilitate positive adaptations to climate variability. For this reason, we have selected two very different climatic zones: Mali, in the Sahel, and Kenya, in East Africa. These particular climatic zones have been selected, in part, because they embody both similarities and contrasts in their climate situation, productive ecologies, and health situations. At each location we have in place long-term research capacity, and access to unique and detailed longitudinal climate-health data sets.

Furthermore, in contrast to most of the literature, this research project takes a multi-disease approach. Although we will focus on the role of the mosquito as a vector, because of its demonstrated sensitivity to climate events, we will also monitor several diseases-and related vectors or proxies-whose transmission is influenced directly (by climate variability e.g., acute respiratory illness, meningitis, and Rift Valley fever, for example) or indirectly through land use change (e.g., diarrheal diseases, anemia).

This study addresses the following overall questions: (1) To what extent are the transmissions of malaria, respiratory and diarrheal diseases among agro-pastoral communities in Sub-Saharan Africa subject to climate variations? (1a) To which climate parameter is each disease most responsive, and does that response vary by climatic zone (Kenya vs. Mali)? (1b) How much of the variability in each disease's response to climate events related to the interactions between the diseases (e.g., among comparable frail populations such as children)? (2) To what extent do communities (including individuals, organizations, and governments) respond to climate variations? (2a) To what extent are responses interactive, engendering a cross-sectoral response to a climate-related intervention? (2b) What individual or community factors affect uptake or response to a climate-related intervention? (3) What differences in disease transmission result from different community responses to climate variations?

BACKGROUND

Evidence increasingly shows that variations in the El Nino - Southern Oscillation (ENSO) signals and other climatic events exert a strong influence on Sub-Saharan African weather patterns. Climate and rainfall variability are associated with sharp fluctuations in grain production and other determinants of health. New models and empirical research have begun to address the societal impacts of climate variability such as disease occurrence and variations in crop yield. The relationship between drought, crop production, and malnutrition has been documented extensively, but only recently have researchers begun focusing on other health impacts of climatic variability.

Throughout Africa, groups are beginning to issue early warnings of expected rain shortfalls to guide planting and resource allocation decisions in the agricultural and public-health sectors. Yet little is known about the effectiveness of these forecasts in improving actual production or in guiding appropriate public health interventions to reduce climate-related diseases. The tight linkages between environmental conditions and human, crop, and livestock morbidity and mortality makes improved understanding of these linkages as well as the development of better predictive tools of critical importance.

Climate variability may affect disease directly (e.g., drought causing dehydration), or indirectly through changing habitat and vegetation (e.g., mosquito breeding grounds) and human behavior (e.g., migration, changes in biomass use and agricultural practices). The extent of these connections is susceptible to modulation by social and demographic factors, including migrations of people moving between climatic subzones. In fact, most climate-related diseases are affected by several mechanisms. Malaria or trypanosomiases transmission is affected by temperature, humidity, and rainfall variations, as well as by land use, human and livestock distribution patterns, and migration. Increased standing water, e.g. associated with irrigation or poor drainage in the event of excessive rainfall, will create more breeding sites for the malaria mosquito vector, temperature can accelerate the reproductive cycle of the malaria plasmodium, and migration can introduce a large number of susceptible hosts. Similarly, the climate response of schistosomiasis transmission is the outcome of the interactions of temperature changes accelerating parasite reproduction and man-made changes such as irrigation affecting breeding sites.

Important recent research has identified the relationship between climatological factors and individual diseases, such as malaria or dengue fever. In addition, the transmission and morbidity associated with a climate-response for a single disease can in turn affect transmission of other diseases. For example, among children under 5 whose immunity to malaria has not yet been established, susceptibility to malaria rises by several health risk factors, including malnutrition, measles, and diarrhea. Mortality from any one of these diseases is heightened when two or more are present. Thus, climate variability can affect a whole array of diseases to which African populations are susceptible including malaria, diarrheal diseases, respiratory and urinary tract infections, schistosomiasis, trypanosomiasis, onchocerciasis, yellow fever, meningitis, and malnutrition. Studying the disease outbreaks and single disease patterns is essential to management of environmental health risks, but it may ignore important interactions and relationships among diseases.

In addition to explicitly considering these interactions, a multi-disease approach to climate events is also a more realistic framework for designing an effective public health intervention. Vertically organized control programs, such as for diarrhea, acute respiratory illnesses, and malaria, have been costly and relatively ineffective. In the past few years, WHO has recommended integrated management of childhood diseases, which recognizes the disease interactions and the necessity for a public health program that manages diseases simultaneously. Similarly, evaluations of child survival programs show an increased effectiveness when education and management of several diseases are linked. In Burkina Faso, for example, the malaria control program was comprised mainly of instructions to families about elimination of standing water around their homes. Yet, in the context of an enhanced health promotion program that improved child nutrition, included vaccination coverage for children to protect them from measles, and lead to better treatment of diarrhea, malaria rates in the community declined. By understanding multiple disease interactions, public health officials will have an opportunity to develop more cost-effective, multi-pronged preventive and ameliorative programs to reduce climate-related disease risk.

Finally, we know little about how populations and health care systems respond to forecasts of climate events, and the extent to which these adaptations alter disease transmission. Public health responses to climate alerts can include measures targeted at the control of the disease vectors (e.g. drainage of water, insecticide spraying), or they can be targeted at people, to interrupt or reduce disease transmission (e.g. through preventive medications, immunizations, use of screens or bednets, water filtration, food supplementation). In addition, medications can be distributed to promptly treat any disease cases. Throughout Africa, malaria control programs have met with limited success partly because response to the distribution of anti-malarials and suggestions for anti-malaria activities depends on the cultural construction and interpretation of the disease. This research will test the effectiveness of multiple-targeted interventions.

Download the complete Research Proposal in PDF format: Text, Figure 1, Figure 2, Figure 4.

Last updated 4/3/2000