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Climate Change: Changing patterns of Infectious Diseases in Humans? Dr Dilys Morgan Health Protection Agency Centre for Infections Climate Change does not just mean global warming Stern review “Climate change threatens basic elements of life for people around the world – access to water, food production, health, and use of land and the environment” Impacts of climate change are not evenly distributed – the poorest countries will suffer earliest and most Climate change may initially have small positive effects for a few developed countries but….” Health risks • Hazards are diverse global and probably irreversible over human time scales • Health impacts are potentially huge • Impact will be inequitable • Impacts may be avoidable Water 0ºC 1ºC 2ºC 3ºC 4ºC 5ºC Significant changes in water availability/ one study projects more than one billion people suffer water shortages in the 2080s, many in Africa, while a similar number gain water Sea level rise threatens major world cities, including London, Shanghai, New York, Tokyo and Hong Kong Small mountain glaciers disappear worldwide – potential threat to water supplies in several years Greater than 30% decrease in runoff in Mediterranean and Southern Africa Food 0ºC 1ºC 2ºC 4ºC 3ºC 5ºC Falling crop yields in many developing regions Severe impacts in marginal Sahel region Rising number of people at risk from hunger (25 – 60% increase in the 2080s in one study with weak carbon fertilisation), with half of the increase in Africa and West Asia Rising crop yields in high-latitude developed countries if strong carbon fertilisation Entire regions experience major declines in crop yields (e.g. up to one third in Africa Yields in many developed regions decline even if strong carbon fertilisation Extreme Weather Events 0ºC 1ºC 2ºC 3ºC 4ºC 5ºC Rising intensity of storms, forest fires, droughts, flooding and heat waves Small increases in hurricane intensity lead to a doubling of damage costs in the US Floods • Contamination of water supplies with sewage • Standing water => mosquito breeding areas • Failure of water treatment facilities • Extreme heat 2003 >44,000 deaths in Europe • Some short term mortality displacement deaths • Milder winters could => reduced deaths ECOSYSTEMS 0ºC 1ºC Coral reef ecosystems extensively and eventually irreversibly damaged 2ºC 3ºC 4ºC Possible onset of collapse of part or all of Amazonian rainforest Large fraction of ecosystems unable to maintain current form Many species face extinction (20 – 50% in one study) 5ºC Risk of rapid climate change and major irreversible impacts 0ºC 1ºC 2ºC 3ºC 4ºC 5ºC Risk of weakening of natural carbon absorption and possible increasing natural methane releases and weakening of the Atlantic THC* Onset of irreversible melting of the Greenland ice sheet Inreasing risk of abrupt, large-scale shifts in the climate system (e.g. collapse of the Atlantic THC and the West Antartic Ice Sheet *Thermohaline circulation Indication of uncertainty of what may happen….. Predicting what may happen… Global Ocean circulation system North Atlantic Conveyor Climate change and health WHO Huge world-wide consequences for human health – hazards are diverse global and But effects on human infections? Problems of estimating effect of climate change on Infectious diseases Transmission of infectious disease determined by many factors: Extrinsic - social, climatic, ecological Intrinsic - human immunity Route of transmission etc etc Temperature, precipitation, humidity - Each affects pathogens and vectors directly and indirectly through ecological change and can affect timing and intensity of outbreaks Estimating effects of climate change on infectious diseases But incidence disease also affected by factors such as sanitation, public health services, population density and demographics, land use changes and travel patterns Models developed to stimulate the effects of climate change on malaria, dengue and cholera but not necessarily prediction tools because of physical and biological feedback and human adaptation Theoretical vs actual….. behavioural adaptations could mitigate many adverse impacts eg vaccines, drugs, public health programmes Prediction not an exact science and uncertainty could underestimate as much as overestimate Difficult to estimate overall risk in specific country or Region Direct vs indirect effect of climate change e.g. migration The evidence… Long list of infections reported to be associated (or have potential to) with climate change Vector-borne diseases Malaria, yellow fever Dengue, filariasis, Ross River fever Lyme Disease, Tick borne encephalitis Leishmaniasis Chagas Disease Onchocerciasis Trachoma Schistosomiasis Rodent – borne infections • Plague • Hantavirus • Leptospirosis Food borne/waterborne infections • Diarrhoeal diseases • Salmonella • Campylobacter • Cholera Interpreting reports Long-term trends difficult to interpret Inconsistency of datasets World is changing with lots of other developments Human behaviour – time and culture dependent Trend to report emerging infections as related to climate change but…sars; ebola/marburg; chikungunya?? Confounders Ecological changes: Economic development and land use; Agriculture; dams, changes in water ecosystems; deforestation & reforestation; flood/drought; famine; climate change Human demographics and behaviour: Societal change; population growth and migration (rural to urban); war/conflict; urban decay; sexual behaviour; IV drug use; overcrowding. Confounders 2 Technology and industry: Globalisation of food supplies; changes in food processing and packaging; organ/tissue transplantation; immunosupp drugs; widespread use of antibiotics. Microbial adaptation and change: Microbial evolution; response to selection in environment Breakdown in public health measures: Curtailment or reduction in preventative or vector control programmes; inadequate sanitation Confounders 3 International travel and commerce: Worldwide movement of goods and people, rapid air travel. Role of climate change among other drivers of global change? Many infections do have seasonal variation e.g. meningitis in sub-Saharan Africa hot dry season Evidence [publications] about relationship between natural variation in meteorological variables (especially temperature) extensive Estimation via modelling and extrapolation less extensive and also encompasses several controversies, including that of adaptation WHO tried to address this “Comparative Quantification of Health Risks: Global and Regional Burden of Disease Attribution to Selected Major Risk Factors” Looks at mortality and burden of disease (DALYs) attributable to CC in 2000 and modeling up to 2030 based on alternative climate scenarios Vector-borne Diseases Vector Major diseases Mosquito malaria, filariasis, dengue fever, yellow fever Ticks Lyme disease, tick-borne encephalitis Sandflies Leishmanisis Triotomids Chagas disease [Trypanosomiasis cruzii] Tsetse African trypanosomisis VBD Complex Dependent on many features Complex life cycles of vectors and parasites and contact with humans Balance between vectors surviving long enough for a parasite to complete life cycle Human factors • Need exposure - No. of bites • Behaviour • Immunity of population (genetic, acquired, drugs, vaccination) • Herd immunity -> endemic stability • Population density Mosquito-borne infections Predicted changes of warm climatic zones, less extreme low temps and more frequent extreme high temps Milder winters-early springs may lengthen survival, and higher temperatures may speed up parasite development Faster vector and pathogen development, with more generations per year + Reduced mortality of vector at low temperatures Range expansion of warm-climate vectors and pathogens in previously temperate areas Shorter life span of vector at high temperatures Climate change and VBD Rainfall patterns altered patterns of mosquito breeding; more flushing of breeding sites with flooding or standing water for breeding sites Would make temperate environments more receptive to tropical VBD while having less negative effects on tropical environments Malaria Studies have reported a relationship between malaria transmission and climate change in highland areas of Kenya No link when examining longer term trends Fraught with confounders and contribution of other factors drug resistance, immune status, population movement, land use etc Malaria Large changes of risk in countries at the edge of current endemic areas. However, most of disease burden will still be associated with small proportionate change in highly endemic areas (particularly Africa) Dengue fever Often urban events with man-made waste acting as water containers for breeding of Stegomyia (Aedes) aegypti Annual average vapour pressure was most important individual predictor of DF distribution, and geographic limits of DG transmission are strongly determined by climate Seems to have smaller climatic influence on disease than for other arboviruses (estimated 1/3 of world’s population at risk) but higher temps accelerate transmission of dengue even in absence of rain. But also need source of infection, vectors and susceptible population for epidemic to occur Modelling indicates climate change will increase latitudinal range of dengue and extend the duration of the transmission season in temperature countries Other VBD Leishmaniasis: visceral and cutaneous Transmitted by phlebotomus, modelling indicates climate change could extend range Chagas Disease [Trypanosomiasis cruzi]: Transmitted by triotomine bug in rural areas South America, modelling indicates climate change would reduce risk Tickborne encephalitis in Europe TBE – studies describing link between TBE and climate change 1960-1998, increase in cases due to milder winter and early spring, but confounders ++ Indicators that fragile transmission cycle of TBE may actually be disrupted by climate change Lyme borreliosis: England and Wales, annual totals, 1997 to 2006 Increase in UK due to: Increased awareness of the disease Greater access to diagnostic facilities More sensitive diagnostic methods Introduction of the enhanced surveillance scheme in late 1996, and more complete reporting of cases since 2000 Increased deer population Increasing popularity of activity holidays such as walking, trekking, and mountain biking The Countryside and Rights of Way Act 2000 Changes in population sizes and geographical ranges of I. ricinus both in the UK and throughout Europe as a result of successive mild winters, warmer summers and early springs Why is so difficult to estimate risks from VBD? Knowledge re vector distribution and abundance lacking even in industrialised countries such as UK. Comprehensive studies are expensive and logistically difficult. Climate-driven change difficult to assess: • Few long-term studies • Geographic limitation • Standardisation of collection methods lacking • Need to be frequent surveys to attribute variations to longer term effects of CC and not just inter-annual climate variability • Vector mapping usually where disease is most prevalent • Reporting bias So is it “absence of evidence of effects of climate change on infectious diseases” or “evidence of absence of effects of climate change” …..?? Food/waterborne infections In industrialised countries positive association between salmonella notifications and mean monthly temperature (more influential earlier in production process rather than at food preparation stage or consumption) Campylobacter and listeria commonest in summer months but temperature association less clear cut Seasonal variation of diarrhoeal disease in less developed countries - but low rainfall vs high rainfall? Studies showing relationship between short-term phenomenon such as El niňo and cholera outbreaks in Bangladesh Food/Water-borne infections UK Food: Warmer summers are likely to be associated with an increase in food-borne diseases Water: increased rainfall (over short periods) leading to increased numbers of bacteria in surface water, increased water temperature leading in an increase in algal blooms in reservoirs and a decrease in the efficiency of chemical coagulation: a major method of removal of microbes from drinking water. Food/waterborne infections Relative importance depends of modes of transmission Heavily influenced by level of sanitation Effects of climate change on diarrhoeal diseases in Less Developed Counties harder to predict, but small increase in RR has huge impact (WHO RR 1.08-1.09 in 2030) Problems with extrapolating from El niňo or other short-term events Longer term risks population learns to adapt – Public Health policy, interventions, education, behavioural change, vaccines, drugs Vulnerability = impact X (1-adaptive capacity) Impact exposure= Exposure X sensitivity Adaptive capacity = adaptation products and practices X resources Less Developed Countries Disportionate impact of effects of climate change More endemic diseases + less ability to adapt and respond Small increase in risk large impact Less Developed Countries Reduction in water supplies Already have 1.1 billion without access to adequate supplies of safe water And 2.4 billion do not have access to sanitation Improved water supply and sanitation has been shown to reduce morbidity of diarrhoea; ascaris infections; guinea worm; trachoma; diarrhoea-specific mortality, and general child mortality Climate Change 2007 – Impacts, Adaptation and Vulnerability (IPPC) Climate change will • continue to change the range of some infectious disease vectors (high confidence) • have mixed effects on malaria; in some places the geographical range will contract, elsewhere the geographical range will expand and the transmission season may be changed (very high confidence) • increase the burden of diarrhoeal diseases (medium confidence) WHO Comparative Quantification of Health Risks “Climate change will bring some health benefits such as lower cold-related mortality and greater crop yields in temperate zones, but these will be greatly outweighed by increased rates of other diseases particularly ID and malnutrition in developing regions” Increased RR of diarrhoea in developing countries Richer countries no or little additional risk of diarrhoea Large changes in RR of P falciparum malaria in countries at the edge of the current distribution Emphasise effects of CC are predicted to be heavily concentrated in poorer populations in LDC and will have most impact on under 5 year olds Health Effects of Climate Change in the UK (Department of Health) Vector-borne diseases: outbreaks of malaria in the UK are likely to remain rare possibility of outbreaks of malaria in other European countries possibility that more effective vectors may arrive in the UK. Tick-borne disease are likely to become more common in the UK, but more likely to be due to changes in land use and leisure activities than to climate change The likelihood that Tick-borne encephalitis will become established in the UK is very low Warmer summers are likely to be associated with an increase in foodborne diseases To manage potential risk from ID as a result from climate change Need early warning systems Improve preparedness Surveillance and response complemented by prediction and prevention Improve forecasting capability and establish faster analytical, observational, and computer developments Multidisciplinary approach– meteorologists, ecologists, entomologist, epidemiologists, public health, social scientists, communications, GIS etc Conclusions Climate change will have huge impact on the world Specific effects of climate change on infectious diseases are difficult to predict CC is just one component of global change which can affect a range of infectious diseases Any contribution of CC to change in ID in industrialised countries is likely to be modest But would have significant and major impact on less developed countries