Exploring the Temperature and Rainfall Influence on Malaria Prevalence in Ethiopia due to Climate Change Pubblico
Dunbar, Jillian (Spring 2022)
Abstract
INTRODUCTION: Climate change is a continuing phenomenon that is negatively impacting the environment of pathogens, vectors, and humans. As many factors are influenced by climate change, the uncertainty surrounding the future burden of infectious diseases, particularly vector-borne diseases, intensifies. The impact of rainfall changes on malaria is ambiguous as it has been difficult for researchers to predict increases and decreases of rainfall in specific areas, and the current rainfall patterns are essential to understand the extent of rainfall changes. The temperature has been easier to assess—temperature increases are strongly linked to creating optimal environmental conditions for Plasmodium to develop faster and increase transmission; yet, as temperatures continue to increase the mosquito itself becomes negatively impacted by the heat. OBJECTIVE: The objective of this research was to explore the effect of two important climatic variables—temperature and rainfall—on the prevalence of malaria in Ethiopia. Comparing data from 2011 and 2015 allowed for a short-term observation of the impact of climate change on the prevalence of malaria in nine geographic regions. METHODS: Descriptive and analytical methods were used to address the research question. Plotting rainfall and temperature across varying time scales was used to visualize temporal changes in average rainfall and temperature; R^2 values for lines of best fit were applied to these plots. A log-binomial regression model was used to examine the prevalence rate of individuals testing positive for a malaria antigen test with every one-millimeter increase in rainfall or with every one-degree increase in temperature. RESULTS: Changes in both temperature and rainfall patterns were observed in Ethiopia from 1981 to 2019—rainfall and temperature generally increased in most regions. Minimal changes in rainfall and temperature were observed between 2011 and 2015 within the same regions; though, larger differences were seen between the geographic regions in Ethiopia. There was a statistically significant association between temperature and cluster prevalence ratios in 2011 for three antigens, but only one antigen in 2015. There were no significant associations between rainfall and cluster prevalence ratios in either year. CONCLUSION: For certain species of Plasmodium, increasing average temperature may be reducing the prevalence ratios of malaria. Overall, more research needs to be conducted to determine the significance of long-term climate change on the prevalence of malaria in Ethiopia. Furthermore, the impact of climate change on the burden of malaria on a larger geographic scale needs to be investigated.
Table of Contents
LITERATURE REVIEW 1
Infectious Disease: Malaria 1
Overview of Malaria 1
Species of Plasmodium 2
Lifecycle in the Human Body 3
The Global Burden of Malaria 4
The Burden of Malaria in Ethiopia 4
Climate Change: Temperature and Rainfall 6
Overview of Climate Change 6
General Impacts of Climate Change on Malaria 7
Climate Change in Ethiopia 9
Impacts of Rainfall on Malaria Burden 11
Impacts of Temperature on Malaria Burden 12
Antigen Testing for Malaria 14
Overview of Antigen Testing 14
Specific Antigens used for Malaria Diagnosis 15
Standard Malaria Indicator Survey 17
THESIS OBJECTIVES 18
MANUSCRIPT 20
Abstract 20
Introduction 21
Methods 25
Dataset #1: Ethiopian MIS 2011 25
Dataset #2: Ethiopian MIS 2015 27
Dataset #3: Ethiopian Annual Rainfall 30
Dataset #4: Ethiopian Annual Temperature 31
Dataset #5: Ethiopian Population 31
Dataset #6: Ethiopian Monthly Rainfall 32
Dataset #7: Ethiopian Monthly Temperature 32
Dataset #8: Ethiopian Shapefile of Administrative Boundaries 32
Ethiopian Regions Included 32
Descriptive and Analytical Methods 34
Results 38
Objective 1: Climate Change Exposure #1: Rainfall 38
1981 to 2019 Long-term Rainfall Observations 38
Objective 1: Climate Change Exposure #2: Temperature 44
1981 to 2019 Long-term Temperature Observations 44
Objective 2: Climate Change Exposure #1: Rainfall 49
2011 and 2015 Short-term Rainfall Observations 49
Objective 2: Climate Change Exposure #2: Temperature 52
2011 and 2015 Short-term Temperature Observations 52
Objective 2: Malaria Antigen Diagnostic Test Outcomes 56
Comparing 2011 and 2015 Malaria Prevalence by Antigen Diagnostic Test 56
MIS 2011 and 2015 Demographics 64
Objective 3: Associations of Rainfall and Temperature with Prevalence of Positive Malaria Antigen Tests 65
Geographic Comparisons of Climate Change 65
Geographic Comparison of Rainfall 66
Geographic Comparison of Temperature 67
Geographic Comparison of Malaria Prevalence 68
Log Binomial Regression Model 98
Analytical Modeling Results 98
Discussion 101
Objective 1: Climate Change Exposure #1: Rainfall 101
1981 to 2019 Long-term Rainfall Observations 101
Objective 1: Climate Change Exposure #2: Temperature 102
1981 to 2019 Long-term Temperature Observations 102
Objective 2: Climate Change Exposure #1: Rainfall 104
2011 and 2015 Short-term Rainfall Observations 104
Objective 2: Climate Change Exposure #2: Temperature 105
2011 and 2015 Short-term Temperature Observations 105
Objective 2: Malaria Antigen Diagnostic Test Outcomes 107
Comparing 2011 and 2015 Malaria Prevalence by Antigen Diagnostic Test 107
Objective 3: Associations of Climate Change with Prevalence of Positive Malaria Antigen Tests 108
Geographic Comparisons of Climate Change: Rainfall and Temperature 108
Log Binomial Regression Model 109
Strengths and limitations 111
Conclusions 112
Recommendations 114
APPENDICES 115
Appendix A: 1981-2019 Average Rainfall--Climate Change 115
Yearly Average Rainfall in Ethiopia from 1981-2019 for each Region
Decadal Average Rainfall in Ethiopia from 1981-2019 for each Region
Seasonal Average Rainfall in Ethiopia in 2011, 2015, and the difference for each Region
Yearly Average Rainfall in Ethiopia in 2011, 2015, and the difference
Appendix B: 1981-2019 Average Temperature--Climate Change 128
Yearly Average Rainfall in Ethiopia from 1981-2019 for each Region
Yearly Average Rainfall in Ethiopia in 2011, 2015, and the difference
Appendix C: Proportions of Positive Antigen Test Detection 133
Positive Antigen Test Proportions of Malaria Cases in Ethiopia for each Region
In 2011, 2015, and the difference
Appendix D: Geographic Association between Climate Change and Proportions of Positive Antigens 137
Positive Antigen Test Proportions plotted with the Average Rainfall
During Bega
During Kiremt
Positive Antigen Test Proportions plotted with the Average Temperature
During Bega
During Kiremt
Appendix E: Geographic Depiction of Regional Boundaries in Ethiopia 161
Appendix F: Geographic Layers of Rainfall in Ethiopia—2011 and 2015 162
Appendix G: Geographic Layers of Temperature in Ethiopia—2011 and 2015 167
Appendix H: Cluster Prevalence of Antigens Legend 172
Appendix I: Geographic Layers of Cluster Prevalence of Antigens in Ethiopia 173
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