Global Climate Change and Extreme Weather Events Understanding the Contributions to Infectious Disease Emergence: Workshop Summary (2008) / Chapter Skim
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2 Climate, Ecology, and Infectious Disease
2 Climate, Ecology, and Infectious Disease
Pages 104-178
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From page 104... ...
• Their effects on the dynamics of plant diseases, and their effects on agriculture and natural ecosystems • As manifested in the public health challenges posed by climate change to human populations in the Arctic Research on the effects of climate variation on infectious disease incidence and geographic range in these diverse contexts is providing the basis for developing climate-based early warning systems for disease risk. Such studies also represent a necessary first step toward anticipating how climate change may alter infectious disease dynamics in various ecological frameworks.
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From page 105... ...
Following the flow of water from inland streams to estuaries and into the open ocean, Dierauf considered the possible impacts of climate change in each of the three main elements of the aquatic continuum and how these changes may affect the health of their animal inhabitants. In freshwater ecosystems, extreme weather events that produce flooding can trigger overwhelming influxes of nutrients into ecosystems.
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. HABs appear to be increasing in both frequency and size as the climate warms, she said; this could result from increased upwelling of nutrients within the ocean or changes in ocean currents, as well as from the effects of extreme weather events inland.
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Analyses of historical climate variation, as reflected in tree-ring patterns, suggest that similar warm, wet conditions existed in Central Asia during the onset of the Black Death in the fourteenth century, as well as in the years preceding a mid-nineteenth-century plague pandemic. As Earth's climate warms, warmer springs and wetter summers are expected to become more common in Central Asia (as well as in North America)
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She describes standard methods for managing plant disease, reviews observed effects of climate variation on plant diseases and their implications given projected future climatic conditions, and discusses research and policy needs for plant disease management in response to climate change. In considering the consequences of climate change for plant health, Garrett emphasizes threshold effects: environmental perturbations that produce disproportionate ecological upheaval.
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. In the face of these public health challenges, Parkinson recommends a range of public health responses, including monitoring of high-risk, climate-sensitive infectious diseases with potentially large public health impacts (e.g., water-borne diseases such as giardiasis)
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, and other precise techniques for pathogen detection, but at the same time, we take a holistic approach that integrates information from the atomic to the atmospheric -- and perhaps, in some cases, even the cosmic -- in order to build a predictive model for cholera outbreaks. Cholera is a significant, global public health problem, as shown in Table 2-1.
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Currently, we are sequencing approximately 50 different strains of Vibrio cholerae, the causative agent of cholera collected from many geographic locations to examine their genetic relationships. Preliminary sequencing studies of V
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Thus, it is not enough to say that its growth correlates with sea surface temperature and salinity; it is important to recognize the ecological interactions that produce these correlations. There is a commensal relationship -- which may prove to be symbiosis -- between Vibrio bacteria and zooplankton.
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From page 113... ...
We are also using our knowledge of cholera epidemiology to help the people of Bangladesh to avoid contracting cholera. In one study, for example, we found that by simply educating women to filter drinking water through several layers of sari cloth, we were able to reduce cholera incidence by 50 percent.
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Nevertheless, with the analyses we have performed to date -- sea surface temperature and sea surface height from satellite sensors; measurements of chlorophyll intensity (corrected for the time lag from chlorophyll-phytoplankton bloom to the zooplankton bloom that feeds on the phytoplankton) ; and measurements of vibrio dispersion in the water -- we are able to determine significant correlations and, thus, a foundation from which to predict cholera epidemics.
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FIGURE 2-2 Environmental parameters (top) and predicted versus actual cholera incidence rate (bottom)
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Department of Agriculture As Earth's climate changes, the frequency and intensity of heat waves, droughts, floods, and other extreme weather events are expected to increase over large regions (IPCC, 2007b)
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and chikungunya fever, which followed heavy rains and drought, respectively. These case studies suggest considerations in developing early warning systems for extreme weather-associated epidemics.
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in Cairo. Rift Valley Fever Outbreaks in East Africa, 2006-2007 In September 2006, the NASA-GSFC/DOD-GEIS monitoring program identified indications of an impending El Niño episode, with SSTs anomalously elevated in the central-eastern Pacific Ocean (+2ºC)
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FIGURE 2-3 Global SST anomalies, September 2006. 2-3 color 119 Broadside
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On December 21, KEMRI confirmed RVF virus infection in specimens taken from several patients in the Garissa district (WHO, 2007a)
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In (B) , green identifies areas included in the NDVI-based RVF risk assessment (based on permissive permanent environmental features)
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2-6 color Chikungunya Fever Outbreaks in Kenya and Other Regions, 2004-2008 In July 2004, while East Africa experienced a severe drought, a public hospital in Lamu, a coastal island city of Kenya, noted a sharp increase in cases of acute febrile illness. Many patients reported joint pain and had negative malaria blood smears (Bedno et al., 2006)
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. Following the Kenya chikungunya fever outbreaks, the epidemics spread to other areas with susceptible human populations and competent vectors: to western Indian Ocean islands, including Reunion, where viral mutation may have facilitated adaptation to the highly efficient Aedes albopictus vector (Tsetsarkin et al., 2007)
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. Developing Early Warning Systems for Extreme Weather-Linked Infections In both the RVF and the chikungunya fever examples, climate appears to have interacted with other factors to facilitate the outbreaks (see Table 2-2)
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Such severe drought conditions also 2-8 of 2007 prevailed during the Chikungunya outbreak in coastal East Africa and the Indian Ocean island during the 2004-2005 period.
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In developing early warning systems for outbreaks linked to extreme weather, consideration of the nonclimatic facilitating factors may enable more precise identification of populations at risk, with better targeting of risk communication. The RVF and chikungunya fever outbreaks also suggest the need for infectious disease early warning systems to integrate with other natural disaster prediction and response programs.
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. has assessed climate-infectious disease links and recommended development of climate-based predictive models for cholera, malaria, and several other infectious diseases (WHO, 2004)
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spread around the Mediterranean Sea in the sixth century A.D., the second ("the Black Death") started in Europe in the fourteenth century and Founding Chair of the Centre for Ecological and Evolutionary Synthesis (CEES)
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FIGURE 2-10 The global distribution of plague. The map shows countries with a known presence of plague in wild reservoir species (black)
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Purportedly, each pandemic was caused by a different biovar of Yersinia pestis, respectively Antiqua (still found in Africa and central Asia) , Medievalis (currently limited to central Asia)
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to 767 A.D.) ; the Black Death and subsequent epidemics from 1346 to the early nineteenth century; and the Third Pandemic, in the mid-nineteenth century in the Yunnan region of China, started in 1855.
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. It is generally accepted that the epidemiology of the Black Death plague, as reflected in historical records, does not always match the "classical" rat-flea-human plague cycle, but the reported medical symptoms were very similar during each historical pandemic.
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FIGURE 2-13 Possible transmission pathways for the plague bacterium, Yersinia pestis. Thick arrows indicate pathways to people.
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. Studying the Plague Dynamics of Central Asia: The Effect of Climate Variation Together with colleagues, I have been studying the dynamics of the plague ecological system based on long-term monitoring data from the former Soviet Union (specifically from Kazakhstan)
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The data are plague prevalence in great gerbils, counts of fleas collected from trapped gerbils, and meteorological observations. Left Upper: Kazakhstan Figure 2-14 on a map of Central Asia with the PreBalkhash focus (between 74 and 78°E and 44 and color, bitpmapped 47°N)
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Moreover, the climatic conditions that support increased prevalence among gerbils, given unchanged gerbil abundance, also favor increased gerbil abundance (see Kausrud et al., 2007) , implying that the threshold density (as found by Davis et al., 2004)
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This suggests that the gerbils will be capable of maintaining population densities where plague can persist over most of their range even if, as predicted, the climate in central Asia becomes increasingly arid.
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Our analyses are thus in agreement with the hypothesis that the medieval Black Death and the mid-nineteenth-century plague pandemic may have been triggered by favorable climatic conditions in central Asia. Figure 2-16 summarizes the link between climate and the two last plague pandemics.
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1949 Year FIGURE 2-16 Tree-ring data suggesting that conditions during the Black Death and the Third Pandemic were similar. The two circles highlight the start of the Black Death and the Third Pandemic; the horizontal line is inserted for the purpose of baseline reference; the vertical gray line indicates the very start of the Third Pandemic (1855)
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Using treering data extending back in time to 1000 A.D., this model allows us to compare model predictions with historical plague epidemiology. Analysis suggests an eco-epidemiological basis for considering the Black Death epidemic as having originated in central Asia during climatically favorable conditions (for the plague system)
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(1999) with permission from the American Journal of Tropical Medicine and Hygiene.
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For example, in central Asia there might be higher levels of plague in the rodent reservoir populations, if current climate prognoses for the region materialize. Also, higher levels in the wildlife reservoir will automatically lead to a greater chance of people being infected by the plague bacillus.
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CLIMATE CHANGE AND PLANT DISEASE RISK Karen A Garrett, Ph.D. Kansas State University Plant Disease and Ecosystem Services One of the most important effects of plant disease is its impact on crop plant productivity.
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Some examples among the many notorious plant diseases illustrate the issues for disease management and the potential impact when diseases cannot be managed effectively. Chestnut blight has had one of the most definitive effects, essentially removing the once common American chestnut from the landscape of eastern North America (Anagnostakis, 2000)
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For some plant diseases such as potato late blight, crop production without pesticides is currently impractical in many systems. In regions where education about pesticide safety is lacking, some farmers and their families experience chronic pesticide exposure.
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. The fact that agriculturalists have the ability to manipulate crop plant genetics makes plant disease management in agriculture much easier, in some respects, than human disease management.
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International Border No Late Blight Antiplano Border Low Incidence Lakes Medium Incidence Regular Incidence High Incidence Source: Developed using the SIMCAST disease forecast model. FIGURE 2-18 Estimated potato late blight severity in the Altiplano area of Peru and Bolivia based on weather measures during 2001-2004 used in a late blight forecasting model.
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. Climatic changes and changes in CO2 concentrations can affect plant physiology, growth, and architecture in several ways that influence plant disease risk.
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Ultimately these relationships will have to be addressed in projects that combine the full range of factors in field studies as well as more limited and controlled experiments that allow clear conclusions about the effects of factors to partition effects. The potential importance of extreme weather events is illustrated by the introduction of soybean rust to the United States.
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Likewise, most agricultural systems are not diverse enough to readily accommodate removal of an important species such as soybeans, if soybean production were to become uneconomical due to a new disease such as soybean rust. Potential Interactions, Thresholds, and Positive Feedback Loops If a small change in average temperature or precipitation patterns results in a small change in plant disease risk, this may be relatively easy to accommodate in agricultural disease management and may have little impact on wildland systems.
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From page 151... ...
As a result, if climatic conditions become more conducive to disease so that pathogens are released from the constraint of the Allee effect, pathogen populations may increase much more rapidly than anticipated. The typical "compound interest" development of plant disease epidemics for pathogens with multiple generations per season can also result in important threshold structures.
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. Likewise, in wildland systems, plant diversity probably provides baseline regulation of plant disease that is unappreciated but may be diminished if systems become saturated with inoculum.
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New microarrays are needed to study the presence and expression of microbial genes related to plant disease. It will be important to collect baseline information about microbial community structure and function soon, so that changes in microbial communities under new climatic conditions can be studied.
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Research to clarify the effects of host landscape structures will help to improve strategies and will be necessary for studying changes at regional, continental, and global scales. Current regional analyses of climatic effects on disease risk tend to be calculated for disease risk in individual "pixels," important for developing a first-approximation estimate of risk.
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, Canada, Greenland, Iceland, Norway, 12 The findings and conclusions in this report are those of the author and do not necessarily represent the official position of the Centers for Disease Control and Prevention. 13 Arctic Investigations Program, Division of Emerging Infections and Surveillance Services, N ational Center for Preparedness Detection and Control of Infectious Disease, Anchorage, AK.
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These changes will be accompanied by greater overall climate variability and an increase in extreme weather events (Arctic Council, 2005)
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K Dallmann and the International Journal of Circumpolar Health.
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For the first time the reduction in annual sea ice has created ice-free shipping lanes to the northwest, from northern Labrador through the Arctic archipelago in northern Canada, to the Bering Strait, and has almost completely cleared a passage to the northeast, from the Bering Strait along the northern coast of the Russian Federation to Norway (see Figure 2-23)
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CLIMATE, ECOLOGY, AND INFECTIOUS DISEASE 159 Figure 2-22A also Figure SA-13-B bitmapped image FIGURE 2-22 The Arctic ice cap, September 2001 (Top) and September 2007 (Bottom)
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. Climate Change and Human Health The direct health effects of climate change will result from changes in ambient temperature, altered patterns of risk from outdoor activities, and changes in the incidence of infectious diseases.
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Weather also affects the distribution of food- and water-borne diseases and emerging infectious diseases, such as West Nile virus,
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Some infectious diseases are unique to the Arctic and lifestyles of the indigenous populations and may increase in a warming Arctic. For example, many Arctic residents depend on subsistence hunting, fishing, and gathering for food, and on a predictable climate for food storage.
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For example, milder weather and less snow cover may have contributed to a large outbreak of Puumala virus infection in northern Sweden in 2007. Puumala virus is endemic in bank voles, and in humans causes hemorrhagic fever with renal syndrome (Pettersson et al., 2008)
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The impact of these changes on human disease incidence has not been fully evaluated, but there is clearly potential for climate change to shift the geographical distribution of certain vector-borne and other zoonotic diseases. For example, West Nile virus entered the United States in 1999 and in subsequent years infected human, horse, mosquito, and bird populations across the United States and as far north as northern Manitoba, Canada (Parkinson and Butler, 2005)
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Response to Climate Change in the Arctic In 1992, the IOM published a report titled Emerging Infections: Microbial Threats to Health in the United States. This report uncovered major challenges for public health in the medical community primarily related to detecting and managing infectious disease outbreaks and monitoring the prevalence of endemic infectious diseases.
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An example of such a network is the International Circumpolar Surveillance system for emerging infectious diseases. This network links hospital and public health laboratories together for the purposes of monitoring invasive bacterial diseases and tuberculosis in Arctic populations (Parkinson et al., 2008)
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The public health response to these emerging microbial threats should include enhancing the public health capacity to monitor climate-sensitive infectious diseases with potentially large public health impacts; the prompt investigation of infectious disease outbreaks that may be related to climate change; and research on the relationship between climate and infectious disease emergence to guide early detection and public health interventions. The development of community-based monitoring networks with links to regional and national public health agencies as well as circumpolar health organizations will facilitate method
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Emerging Infectious Diseases 2(1)
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Paper presented at the International Confer ence on Emerging Infectious Diseases, Atlanta, GA. CDC (Centers for Disease Control and Prevention)
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Lancet Infectious Diseases 6(4)
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Emerging Infectious Diseases 7(1)
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Emerging Infectious Diseases 13(5)
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2004. Emerging infectious diseases of plants: pathogen pollution, climate change and agrotechnology drivers.
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Plant Disease 88(5)
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Plant Disease 89(3)
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Emerging Infectious Diseases 14(1)
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Emerging Infectious Diseases 7(1)
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Emerging Infectious Diseases 11(7)
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