Climate change futures: health, ecological and economic dimensions

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98% of the two-year life cycle takes place off the host, climate acts as an essential determinant of distribution of established tick populations across North America (Fish 1993). LYME DISEASE IMPLICATIONS OF CLIMATE CHANGE John Brownstein BACKGROUND Lyme disease is the most prevalent vector-borne disease in the continental United States. Lyme was discovered in 1977 when arthritis occurred in a cluster of children in and around Lyme, CT. Since that emergence, Lyme disease has spread throughout the Northeast of the US, two north-central states (Minnesota and Wisconsin) and the Northwest (California and Oregon). In these areas, between 1% and 3% of people who live there become infected at some time. Lyme disease is also common in Europe, especially in forested areas of middle Europe and Scandinavia, and has been reported in Russia, China, and Japan. The deer tick, Ixodes scapularis, is the primary vector of Borrelia burgdorferi, the spirochete bacteria that is the agent of Lyme disease in North America (Keirans et al. 1996; Dennis et al. 1998). I. scapularis is also a known vector of human babesiosis, and human granulocytic ehrlichiosis (Des Vignes and Fish 1997; Schwartz et al. 1997). Although recent emergence of Lyme disease throughout the northeastern and mid-Atlantic states has been linked to reforestation (Barbour and Fish 1993), additional influence of environmental change can be expected considering the anticipated shifts in climate. HEALTH AND ECOLOGICAL IMPACTS Lyme disease most often presents with a characteristic "bull’s-eye" rash, called erythema migrans, surrounding the attached tick. The initial infection can be asymptomatic, but is often accompanied by fever, weakness, and head, muscle and joint aches. At this stage, treatment with antibiotics clears the infection and cures the disease. Untreated Lyme disease can affect the nervous system, the musculoskeletal system or the heart. The most common late manifestation is intermittent swelling and pain of one or several joints, usually large, weight-bearing joints such as the knee. Some infected persons develop chronic neuropathies, with cognitive disorders, sleep disturbance, fatigue and personality changes. Figure 2.9 New Cases of Lyme Disease in the US: 1992-2003 25,000 20,000 15,000 10,000 45 | INFECTIOUS AND RESPIRATORY DISEASES Although the local abundance of vectors may be guided by “density-dependent” factors such as competition, predation, and parasitism, the geographic range of arthropod (tick) habitat suitability is controlled by other factors, such as climate. ROLE OF CLIMATE Climatic variation largely determines the maintenance and distribution of deer tick populations by regulating off-host survival (Needham and Teel 1991; Bertrand and Wilson 1996). The abiotic environment (that includes soils, minerals and water availability) plays a vital role in the survival of I. scapularis with both water stress and temperature regulating off-host mortality. As 5,000 0 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 Source: Centers for Disease Control and Prevention ECONOMIC DIMENSIONS Chronic disability is the primary concern with Lyme disease and as new populations are exposed in areas where the medical profession has little experience with this disease, such cases are projected to rise in the near-term. The productivity losses associated with chronic disabilities affect individuals, communities, work places and health insurance companies. CASE STUDIES
One analysis (Vanderhoof and Vanderhoof-Forschner 1993) conservatively estimated costs per case at about US $60,000. Based on an annual mean incidence of 4.73 cases of Lyme disease per 100,000 population, a later decision analysis model (Maes et al. 1998) yielded an expected national expenditure of US $2.5 billion (1996 dollars) over five years for therapeutic interventions to prevent 55,626 cases of advanced arthritis, neurological and cardiac disease. These figures may underestimate the true costs of the long-term disabilities incurred. Figure 2.10 Current Lyme Disease Habitat THE FUTURE 46 | INFECTIOUS AND RESPIRATORY DISEASES CCF-I: ESCALATING IMPACTS The northward spread of warming conditions and warmer winters creates ideal conditions for the northward spread of Lyme disease into Canada, with continuing transmission in most of the regions with transmission currently. In some areas the abundance of ticks may increase as well, intensifying transmission. Expansion of the range of Ixodes ricinus in Sweden has already been documented and the northern migration is correlated with milder winters and higher daily temperatures (Lindgren and Gustafson 2001). Model projections of the areas suitable for Lyme disease transmission show that maximum, minimum and mean temperatures, as well as vapor pressure, significantly contribute to the maintenance of populations in particular geographic areas. Distribution of southern climate-based habitat suitability for Ixodes scapularis as predicted by the climate-based statistical model. Nonoverlapped yellow pixels represent suitable areas that have yet to be colonized. The blue line across present-day Ontario represents the northern limit of habitat suitability predicted by Lindsay et al. (1995). Source: Brownstein et al. 2005 Figures 2.11 Lyme Model Projections (a) Constant Suitability Expanded Suitability Constant Unsuitability Expanded Unsuitability (b) CASE STUDIES (c) Projected distribution of climate-based habitat suitability for Ixodes scapualris during three future time periods: the 2020s (a), the 2050s (b), and the 2080s (c). The models project an increase in suitable habitat of 213% by the 2080s. Source: Brownstein et al. 2005
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RISK SPREADING IN DEVELOPED AND DEV
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THE LIMITS OF INSURABILITY Not all
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(also known as “cash-flow underwr
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from areas plagued by persistent dr
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Engagement of the insurance industr
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Industry observers point out that p
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CONCLUSIONS AND RECOMMENDATIONS Jus
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FINANCIAL INSTRUMENTS Regulators an
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of carbon-risk hedging products, su
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Summary Table of Extreme Weather Ev
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Table B.1 Summer Percentage Frequen
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Climate sensitivity for small-scale
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diffuse and do not manifest in sing
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APPENDIX D. LIST OF PARTICIPANTS AT
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Carmenza Robledo Gruppe Oekologie E
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126 | BIBLIOGRAPHY Bibliography AAA
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128 | BIBLIOGRAPHY Chordas, L. Epid
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Ford, S.E. & Tripp, M.R. Diseases a
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132 | BIBLIOGRAPHY Kalkstein, L. S.
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134 | BIBLIOGRAPHY Mills, E. The in
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136 | BIBLIOGRAPHY Rose, J. B., Eps
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138 | BIBLIOGRAPHY Vandyk, J. K., B
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Infectious and Respiratory Diseases
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Climate change futures: health, ecological and economic dimensions

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