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There are three categories of research into the linkages between climatic conditions and infectious disease transmission. The first examines evidence from the associations between climate variability and infectious disease occurrence. The second looks at early indicators of infectious disease impacts of longterm climate change. The third uses the above evidence to create predictive models to estimate the future burden of infectious disease under projected climate change scenarios.

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What is Climate Change? - New England Journal Of Medicine

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What is Climate Change? - New England Journal Of Medicine

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Climate change is occurring as a result of an imbalance between incoming and outgoing radiation in the atmosphere.¹ As solar radiation enters the atmosphere, some of it is absorbed by the earth's surface and reemitted as infrared radiation, which is then absorbed by greenhouse gases — primarily carbon dioxide, methane, and nitrous oxide — which result from the combustion of fossil fuels and which cannot be effectively removed from the atmosphere because of deforestation. This process generates heat. As the concentrations of greenhouse gases in the atmosphere have reached record levels, global temperatures have risen at a faster rate than at any time since records began to be kept in the 1850s, and temperatures are expected to increase by another 1.8 to 5.8°C by the end of this century. The hydrologic cycle will be altered, since warmer air can retain more moisture than cooler air. Some geographic areas will have more rainfall, and some more drought, and severe weather events — including heat waves and storms — are expected to become more common. For these reasons, the term “climate change” is now preferred over the term “global warming.” Because of rising temperatures and changing rainfall patterns, climate change is expected to have a substantial effect on the burden of infectious diseases that are transmitted by insect vectors and through contaminated water.

“Global Climate Change and Infectious Diseases | NEJM.” New England Journal of Medicine, www.nejm.org/doi/full/10.1056/NEJMp0912931.

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What diseases are becoming more prominent due to to climate change?

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What diseases are becoming more prominent due to to climate change?

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Lyme disease: A recent CDC report found that the number of cases of illnesses transmitted by ticks more than doubled between 2004 and 2016 in the US; the biggest jump was seen in cases of Lyme disease. Researchers identified warming temperatures and shorter winters as one of the reasons. Also, the change in weather allowed ticks to invade areas that had previously been too cold for them to live.

West Nile virus: Temperatures soared this past summer in Europe. At the same time, there was a sharp spike in West Nile virus infection, with more than 400 cases reported. Health experts believe the two are connected. The disease is spread by mosquitoes that have fed on infected birds, and warmer temperatures have helped to start the transmission season early.

Malaria: In Ethiopia and Colombia, scientists observed that malaria’s range shifted to warmer areas between 1990 to 2005. In part because the transmitting mosquito thrives in the heat. But also, because the parasite that causes malaria reproduces faster inside the vector mosquito when the weather is warmer.

Flesh-Eating Bacteria: It’s not just humans who enjoy a nice swim in the ocean when the weather is hot. Flesh-eating bacteria called vibriosis flourish in warm seawater. As temperatures climb and sea levels rise, they increase in number and can infect people through open wounds or by contaminating popular seafood like oysters.

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Public health

Abstract

Global climate change is inevitable - the combustion of fossil fuels has resulted in a buildup of greenhouse gases within the atmosphere, causing unprecedented changes to the earth's climate. The Fourth Assessment Report of the Intergovernmental Panel on Climate Change suggests that North America will experience marked changes in weather patterns in coming decades, including warmer temperatures and increased rainfall, summertime droughts and extreme weather events (e.g., tornadoes and hurricanes). Although these events may have direct consequences for health (e.g., injuries and displacement of populations due to thermal stress), they are also likely to cause important changes in the incidence and distribution of infectious diseases, including vector-borne and zoonotic diseases, water-and food-borne diseases and diseases with environmental reservoirs (e.g., endemic fungal diseases). Changes in weather patterns and ecosystems, and health consequences of climate change will probably be most severe in far northern regions (e.g., the Arctic). We provide an overview of the expected nature and direction of such changes, which pose current and future challenges to health care providers and public health agencies.

Human activities have caused a sharp increase in greenhouse gases, including carbon dioxide, nitrous oxide and methane, in the atmosphere, which has led to unprecedented changes in the earth's climate. The Intergovernmental Panel on Climate Change was established by the United Nations Environment Program and the World Meteorological Organization in 1988 to provide objective analysis of data related to climate change. The panel comprises scientists from around the globe and aims to present the scientific, technical and socioeconomic issues arising from the data to government decision-makers in a policy-neutral context.

In April 2007, the panel issued a report on the impact of global climate change on human and animal populations. This report was based on about 30 000 observations of changes in physical and biological systems worldwide. More than 90% of these changes are attributable to human activities such as the combustion of fossil fuels., The panel's fourth assessment report includes projections for regions including North America. These projections include warmer temperatures (), more rainfall because of an increased fraction of precipitation falling as rain rather than snow, and more frequent droughts, wildfires and extreme weather events such as hurricanes and tornados. Warming is predicted to be most severe in the northernmost latitudes.

Some of the health effects attributable to climate change are directly related to changing environmental conditions. The Public Health Agency of Canada anticipates increased burden of disease as a result of thermal stress and more frequent extreme weather events, and some projected direct effects of climate change on human health, such as heat-related morbidity and injuries, have been previously reviewed. However, climate and weather patterns are important physical components of complex ecosystems and any major change in the nonliving component of an ecosystem will affect living components, including microbes, insect vectors, animal reservoirs and susceptible humans, and change the incidence and distribution of infectious diseases.

The close relation between climate, environment and infectious disease in the developing world are well recognized. For example, the importance of rainfall and drought in the occurrence of malaria,, the influence of the dry season on epidemic meningococcal disease in the sub-Saharan African "meningitis belt" and the importance of warm ocean waters in driving cholera occurrence in the Ganges River delta and elsewhere in Asia are well described. Indeed, there is widespread concern about the potential impact of global climate change on the distribution and burden of these and other infectious threats in the developing world.,

The relation between ecosystems, infectious diseases and global climate change are less intuitive in the context of more developed countries where clean drinking water, reduced exposure to insect vectors, higher-quality housing and other advantages partly mitigate such threats. However, climate changes projected to occur in the coming decades are likely to influence the burden and incidence of infectious diseases in more developed regions including North America. In this review, we describe the nature and direction of changes in infectious disease epidemiology that are likely to accompany global climate change and describe the challenges that these changes will pose to health care providers and public health agencies. We focus principally on Canada and the United States, including the Arctic regions of North America, where the effects of global climate change are likely to be most severe. We also include several illustrative examples from other highly developed regions such as the European Union and Australia. In particular, we review several zoonotic diseases of public health importance, the association between precipitation and water-borne diarrheal diseases, seasonal respiratory diseases with person-to-person transmission and endemic mycoses ().

This review is not meant to obscure the likelihood that the brunt of the increased incidence of infectious diseases related to climate change will occur in the same less-developed, economically poor countries that are currently most affected by infectious diseases., For more information about the projected changes in infectious disease epidemiology in these diverse regions of the world, we encourage readers to consult the panel report and other reports and reviews devoted to this topic.,,,

Zoonotic and vector-borne diseases

Climate change may affect zoonoses (infectious diseases of animal origin that may be transmitted to humans) in 3 ways: it may increase the range or abundance of animal reservoirs or insect vectors, prolong transmission cycles, or increase the importation of vectors or animal reservoirs (e.g., by boat or air) to new regions, which may cause the establishment of diseases in those regions. For example, the burden of Lyme disease (a tick-borne borreliosis) is likely to change substantially in North America and Europe. Currently, endemic Lyme disease is uncommon in Canada, and established populations of competent vectors (vectors that are capable of allowing the pathogen to complete its lifecycle, such as Ixodes scapularis and Ixodes pacificus) are limited largely to southern Ontario, Nova Scotia and British Columbia. However, temperature determines the northernmost extent of tick populations. Mathematical models suggest that tick abundance may greatly increase in southern Canada, with a northern expansion of about 200 km by the year 2020. This rate of expansion would be sufficient to establish vector populations in Alberta and Saskatchewan ().

In North America, other infectious diseases that may expand their ranges because of northern expansion of vector populations include such tick-borne threats as babesiosis, anaplasmoses and Powassan encephalitis in addition to mosquito-borne threats such as dengue. In Europe, the expansion of the range of ticks and other vectors (e.g., sandflies) may increase the incidence and distribution of Lyme disease, boutonneuse fever and leishmaniasis. In Australia, the southern expansion of mosquito ranges is expected to result in an increase in such endemic diseases as Ross River virus, Barmah Forest virus and Murray Valley encephalitis.,

The transmission of vector-borne zoonoses may also be enhanced by earlier onset of spring, resulting in a prolonged amplification cycle. West Nile virus, which appeared in Canada in 2002, has an amplification cycle that involves mosquitoes and birds. Human infections become more likely as the proportion of "bridge" vectors (mosquitoes that bite both birds and humans) increases. In temperate regions, virus amplification begins with the onset of mosquito activity in spring. Human risk peaks in late summer or early autumn, and risk decreases with the disappearance of mosquitoes in autumn. An earlier onset of spring would prolong the amplification cycle resulting in an increased incidence of human infection. The impact of increased precipitation on mosquito ecosystems is complicated. Transmission risk could increase because of increased mosquito breeding sites. Alternatively, increased numbers of mosquito predators and decreased geographic concentrations of amplifying hosts (i.e., birds) attributable to a rise in the distribution of water sources may lower the risk of transmission.,

Whether climate change will facilitate re-establishment of autochthonous (locally acquired) malaria in the United States and Canada, where it was once endemic, is unclear. However, prolonged amplification cycles and warmer winter temperatures may facilitate the establishment of imported mosquito-borne diseases in countries from which they have historically been absent. For example, in 2007 chikungunya fever, a mosquito-borne disease endemic in parts of Africa and Asia, caused a large outbreak of disease in northeastern Italy, presumably following importation of infected mosquitoes via boat or air. The onset of winter weather likely contributed to the control of this outbreak, but warming trends may make the control of future importation-related outbreaks more difficult.

Residents of temperate regions of North America may also be affected by increased incidence and distribution of vector-borne diseases in other countries because of high rates of travel to subtropical and tropical countries. For example, it is estimated that Canadians took over 2 million trips to Mexico, Cuba and the Dominican Republic in 2006 alone. As dengue and malaria activity are projected to increase in Latin America, the Caribbean, Asia and Africa, an increase in travel-related dengue fever and malaria in returning travellers is likely.,, Marked discrepancies in dengue incidence in contiguous geographical areas (e.g., along the US-Mexican border) suggest that both vector abundance and economic factors, such as the availability of air conditioning, contribute to disease risk. Travellers who use more luxurious accommodations and insect repellents that contain diethyltoluamide (DEET) may be relatively protected. Nonetheless, the impact of such increases on local populations, combined with emerging resistance to antimalarial agents and the recent resurgence of malaria in a number of urban areas in Jamaica and India,, are cause for substantial concern both for travel medicine practitioners and for those concerned about global health.

Climate change is also likely to impact the distribution and burden of zoonotic diseases that are not dependent on insect vectors for transmission. Pathogens such as the Sin Nombre virus, a cause of hantavirus pulmonary syndrome, are harboured by rodent species that are especially abundant in the southwestern United States and in western states and provinces. Rodent population density appears to be a key driver of disease in humans, who are often infected after exposure to dust contaminated by rodent urine (e.g., while sweeping out storage spaces). Recent surges in hantavirus infection have been attributed to the El Niño-type weather conditions, which may become predominant with future climate change, suggesting that hantavirus pulmonary syndrome incidence may increase in coming decades. Climate change may similarly increase the risk of plague in western states and provinces.

Water-and food-borne diseases

Water-and food-borne diseases are a major cause of mortality worldwide and an important cause of morbidity in developed countries. Water-borne pathogens include viral, bacterial and protozoan agents of gastroenteritis and pneumonic pathogens such as Legionella species. Many of these pathogens (e.g., verotoxigenic Escherichia coli, Campylobacter species and viral pathogens) are also important causes of food-borne illness, as are bacterial pathogens such as Salmonella and Shigella species.

Water-borne diseases occur despite state-of-the-art water treatment technology. For example, a 1989 cryptosporidiosis outbreak tied to a municipal water supply in Milwaukee, Wisconsin, affected an estimated 400 000 people. The Walkerton, Ontario, disaster in 2000 underscored the vulnerability of populations to water-borne disease., The incidence of both water-and food-borne diseases is expected to increase as a result of climate change. Large water-borne disease outbreaks have been linked to extreme precipitation events, which are expected to increase in frequency in coming decades (). In addition, most cases of water-and food-borne gastroenteritis, particularly illness related to Campylobacter and Salmonella, exhibit a distinct summertime pattern of occurrence. Although it is possible that seasonality is due to behavioural patterns (e.g., barbecuing or swimming in the summer), the association between warmer temperatures and disease suggests that rates of water-and food-borne illness are likely to increase with rising temperatures.

The incidence of pneumonic infections due to water-borne infectious agents, such as legionellosis (Legionnaire disease) and melioidosis, is also likely to be affected by climate change. Legionellosis incidence peaks during warmer months and risk appears to increase with rainy, humid weather. Melioidosis is an infectious disease caused by the bacterium Burkholderia pseudomallei and is endemic in southeast Asia and Australia. Cyclones appear to be associated with increased risk of severe melioidosis, perhaps because of aerosolization of the bacterium by stormy weather.

Globally, the water-borne enteric disease most likely to increase in the face of global climate change is cholera, a diarrheal disease with a high case-fatality rate caused by infection with toxigenic strains of Vibrio cholerae, which remains an important cause of death in the developing world. Risk increases with warmer water temperatures, suggesting that global cholera activity may increase sharply in the face of climate change. Such increases pose a risk not only to developing countries, but also to developed countries via importation of disease. Nontoxigenic strains of V. cholerae and other noncholera Vibrio (e.g., Vibrio parahemolyticus and Vibrio vulnificus) may also become more frequent agents of disease as a result of increasing ocean temperatures and increasing frequency of extreme weather events. For example, cases of illness due to these micro-organisms occurred in association with Hurricane Katrina in 2005.

Seasonality of communicable diseases

Many respiratory pathogens, including influenza, respiratory syncytial virus and Streptococcus pneumoniae, exhibit winter seasonality that is often attributed to seasonal changes in temperature or population behaviour (e.g., indoor crowding). In fact, these phenomena are poorly understood and causal mechanisms are difficult to establish owing to seasonal coincidence of multiple exposures. If cold temperatures are an important driver of respiratory disease, climate change might be expected to attenuate the impact of influenza epidemics. Data based on influenza activity during the El Niño Seasonal Oscillation (an intermittent inversion of Pacific Ocean thermal gradients) suggest that this may be the case., El Niño is associated with changes in weather patterns similar to those projected to occur in coming decades. In this sense, study of disease trends in the presence and absence of El Niño may provide insight into future disease patterns.

Climate change also has the potential to indirectly affect communicable disease transmission. The forced migration of people because of drought or flooding could increase the transmission of many communicable diseases because of enhanced intermingling of populations that have previously been isolated from one another. Large-scale migrations have been associated with surges in communicable diseases and emergence of novel infections throughout recorded history. Forced migration may ultimately be a more important driver of changes in infectious disease epidemiology than other effects described in this review.

Endemic mycoses

Several fungal pathogens of public health importance produce spores that rely on local soil ecology and climate for persistence in the environment. As ecosystems change, the burden of invasive fungal disease may increase. The dry summers and heavy wintertime precipitation projected for North America match the optimal conditions for spore dispersal by Blastomyces dermatitidis, a fungus that causes disease of the bones, lungs and skin. In Canada, B. dermatitidis occurs most commonly in northwestern Ontario. The incidence of disease due to Coccidioides imitis, which is endemic to the southwestern United States and causes pulmonary, central nervous system and bone disease, may also be altered by changing rainfall, drought and temperature patterns.

Warmer, drier summers may have facilitated the establishment of Cryptococcus gattii in Canada. This fungus had previously been seen only in tropical and subtropical regions (particularly those in Australia), but emerged on Vancouver Island in 1999, where it has caused more than 100 cases of human illness in addition to illness in domestic animals.

Arctic regions

Arctic regions are uniquely vulnerable ecosystems that have experienced warming trends that are more substantial than those experienced elsewhere in North America. An increased incidence of water-and food-borne disease and zoonoses appears inevitable. The economic, social and environmental impact of disease emergence in Arctic regions will place a heavy burden on already underserved communities. Hunting and traditional means of food preparation may also increase the probability of contracting an infectious disease.

Increases in ocean temperatures have been linked to outbreaks of gastroenteritis as a result of infection by noncholera Vibrio species, which may have been acquired through consumption of contaminated seafood. Likewise, the risk of botulism from consumption of traditional fermented meats is enhanced by increased ambient air temperatures.

Changing ecosystems also disrupt the ecology of wildlife populations in ways that are likely to increase the risk of zoonotic disease. Climate-driven increases in rabbit and predator populations (e.g., fox) may augment the risk of tularemia and rabies. Warmer temperatures and longer summers increase the number of amplification cycles for parasites of food animals (e.g., Trichinella and Echinococcus species) and lead to longer summer hunting seasons. These parasites cause diseases that are largely concentrated in northern communities,, and the burden of parasitic diseases in the North may increase with warming.

Conclusion

Climate change will increase the risk of infectious disease by expanding the ranges of species known to carry zoonotic diseases, changing pathogen dynamics in environmental reservoirs and altering pathogen transmission cycles. How should the medical and public health communities prepare for such threats? As a first step, agencies must have the ability to measure changes in disease burden. The fact that several diseases described above (e.g., Lyme disease, blastomycosis, echinococcosis and, since 1999, trichinosis) are not subject to national surveillance in Canada will make such reporting difficult. It may be helpful to reconsider the status of several of these important diseases.

At a more basic level in North America, the wide ranging and unpredictable health effects that are likely to result from climate change highlight the need for strengthening public health infrastructure related to disease surveillance, food and water safety, control of insect vectors and animal reservoirs of disease, and public health outbreak response. Although mitigation of greenhouse gas emissions cannot be regarded as the primary responsibility of the health care system or medical practitioners, physicians and other health care providers are highly credible opinion leaders and advocacy on environmental issues can be seen as a natural extension of the medical profession's interest in enhancing the health of the communities it serves.

In less developed countries, changes in infectious disease burden due to climate change will be greater than those seen in the developed world, and enhancement of public health infrastructure (particularly related to surveillance and outbreak forecasting, provision of safe food and water, and vector control) will be the key to mitigating the effects of climate change. The global scope of these challenges and the fact that infectious diseases do not respect national borders highlight the need for multinational and collaborative scientific efforts to control disease. There are currently many national and international initiatives underway that are directly or indirectly related to climate change, infectious diseases and global health ().

Finally, the importance of animal and environmental reservoirs of disease suggests that interdisciplinary communication between health professionals, veterinarians, environmental scientists, ecologists, geographers and economists seeking to understand climate change will be key to protecting people in North America and worldwide against these threats. Rigorous cross-disciplinary studies using a variety of methodologic tools will enable us to predict the transmission dynamics of diseases under different climate scenarios and estimate the cost-effectiveness of mitigation strategies. The performance of such high-quality research will depend on the extent to which such endeavours are embraced by decision-makers, the research community and funding agencies.
Key points of the article
* Global climate change is occurring as a result of greenhouse gases created by human activities. Changes in climate and associated changes in weather and other environmental exposures will have important consequences for human health.

* Climate change will alter the relations between microbes, insect vectors, animal reservoirs of infectious diseases and humans, and will alter the burden and distribution of infectious diseases of public health importance.

* Warmer temperatures and altered rainfall patterns are likely to increase the range and burden of vector-borne infectious diseases in North America and elsewhere.

* Altered patterns of rainfall and increased frequency of extreme weather events are likely to influence the incidence of water-borne gastrointestinal and respiratory diseases in North America and elsewhere.

* The best defence against increases in infectious disease burden related to climate change lies in strengthening existing public health infrastructure. Physicians, as opinion leaders, can also influence public policy related to greenhouse gas emissions.

Acknowledgments

All of the authors receive financial support from the US National Institute of Allergy and Infectious Diseases (R21AI065826-01A1) and from the Early Researcher Award program of the Ontario Ministry of Research and Innovation.

Footnotes

Une version française de ce résumé est disponible à l'adresse www.cmaj.ca/cgi/content/full/178/6/715/DC1

Contributors: All of the authors contributed to the conception of this article, the acquisition of data, and drafting and revision of the manuscript. All of the authors provided final approval of the version to be published.

Competing interests: None declared.

Correspondence to: Dr. David N. Fisman, The Hospital for Sick Children Research Institute, Rm. 428, 123 Edward St., Toronto ON M5G 1E6; fax 416 813-5979; ac.sdikkcis@namsif.divad

REFERENCES

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Public health: Climate change and infectious diseases in North America: the road ahead

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Public health Global climate change is inevitable - the combustion of fossil fuels has resulted in a buildup of greenhouse gases within the atmosphere, causing unprecedented changes to the earth's climate.

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Rate of increase for West Nile Virus

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How does climate change affect infectious disease?

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How does climate change affect infectious disease?

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Malaria, West Nile virus, cholera, and other mosquito related diseases are becoming more deadly and are spreading quicker. This is because with global warming the mosquitoes can travel further and longer, and more effectively spread the disease.

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The Effect Of Global Warming on Infectious Diseases

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The Effect Of Global Warming on Infectious Diseases

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Abstract

Global warming has various effects on human health. The main indirect effects are on infectious diseases. Although the effects on infectious diseases will be detected worldwide, the degree and types of the effect are different, depending on the location of the respective countries and socioeconomical situations.

Among infectious diseases, water- and foodborne infectious diseases and vector-borne infectious diseases are two main categories that are forecasted to be most affected. The effect on vector-borne infectious diseases such as malaria and dengue fever is mainly because of the expansion of the infested areas of vector mosquitoes and increase in the number and feeding activity of infected mosquitoes. There will be increase in the number of cases with water- and foodborne diarrhoeal diseases.

Even with the strongest mitigation procedures, global warming cannot be avoided for decades. Therefore, implementation of adaptation measures to the effect of global warming is the most practical action we can take. It is generally accepted that the impacts of global warming on infectious diseases have not been apparent at this point yet in East Asia. However, these impacts will appear in one form or another if global warming continues to progress in future. Further research on the impacts of global warming on infectious diseases and on future prospects should be conducted.

Key words: dengue fever, global warming, Japanese encephalitis, vector-borne infectious diseases, water- and foodborne infectious diseases

1. Introduction

Global warming is an unequivocal phenomenon today. Global warming is one of the components of climate change, and it induces considerable impacts on human health. The emerging evidence of the effect of global warming on human health has been summarized in the fourth report of Intergovernmental Panel on Climate Change (IPCC). 1 The effect of global warming on human health is divided into two categories: direct effect on the illness such as heat shock and increased mortality in population with other diseases and indirect effect on diseases such as infectious diseases and allergy (). The IPCC report states that climate change has altered the distribution of some infectious disease vectors, the seasonal distribution of some allergenic pollen species, and increased heat wave-related deaths. In the present review, the effect of global warming on infectious diseases is addressed. Furthermore, current research on the effect of global warming on infectious diseases is introduced.

Table 1

Direct effect on other health conditions

Heat waves: Short-term increase in mortality, especially among those with cardiovascular and/or respiratory diseases, and increase in heat shock patients

Co-effect with air pollution: Increase in asthma and allergy patients

Storms and floods: Increase in morbidity and accidental death

Indirect effect on infectious diseases

Expansion of mosquito- and tick-infested areas, and increase in mosquito activity: Increase in the number of patients with mosquito-borne infectious diseases (i.e. dengue and malaria) and expansion of epidemic areas

Contamination of water and foods with bacteria: Increase in the number of patients with water- and foodborne infectious diseases

Deterioration of environmental and social conditions: Increased risk of infectious diseases

2. Effect of Global Warming on Infectious Diseases

It has been assumed that global warming has profound effects on infectious diseases (). The effect of global warming on infectious diseases is indirect. Although the effects have been detected worldwide, the degree and types of the effect are different, depending on the location of the respective countries and socioeconomical situations. Among infectious diseases, water- and foodborne infectious diseases and vector-borne infectious diseases are two main categories that are forecasted to be most affected.

2.1. Effect of global warming on water- and foodborne infectious diseases

It has been predicted that the number of the patients with water- and foodborne infectious diseases is heavily affected by global warming. The number of cholera cases was increased by both high and low rainfalls in Bangladesh. 3 The number of non-cholera diarrhoeal disease cases is also increased by high and low rainfalls and by higher temperature in Bangladesh. 4 However, the degree of the effects on water- and foodborne infectious diseases depends on the levels of the social infrastructure. In the countries where water and food supply systems and sewage system are well established, the effect on water- and foodborne infectious diseases is expected to be less affected. Thus, the effect is assumed to be greater in developing countries but less in developed countries.

2.2. Effect of global warming on vector-borne infectious diseases

Vector-borne infectious diseases are caused by the pathogens transmitted by arthropods. Mosquitoes and ticks are the main vectors. The effect of global warming on vector-borne infectious diseases is indirect. Global warming affects geographical distribution and activity of the vectors. Thus, the levels of the influence depend on the kind of vectors.

The major mosquito-borne infectious diseases that have been reported to be affected by global warming include malaria, dengue fever, Japanese encephalitis (JE), and tick-borne encephalitis.

2.3. Current studies on the effect of global warming on the infectious diseases

3. Direct Effect of Global Warming on Human Health Other Than Infectious Diseases

It has been reported that global warming has direct effects on various aspects of human health including infectious diseases. They include heat-related diseases caused by heat waves, injuries, and deaths caused by extreme geological events.

Heat shock is a health problem that is most directly affected by the ambient temperature. In the studies in Japan, there has been a positive relationship between the temperature and the number of heat shock cases in most of the major cities in Japan. The number of heat shock cases increases sharply when the temperature becomes 32°C and higher. Based on these observations, it is assumed that global warming will increase the number of heat shock patients. However, adaptation measures such as introduction of air-conditioning system are expected to ease the effect.

It has also been reported that global warming increases the mortality rate, especially among those with cardiovascular and/or respiratory diseases. Many studies have demonstrated that there is a temperature at which the mortality rate is at the lowest level. This temperature is called the optimum temperature. The mortality rate is higher at both extremes of temperature, that is, high and low sides. Thus, the temperature-mortality relation is usually "V" shaped. The 80-85 percentile value of the daily maximum temperature is the best index of the optimum temperature. 27,28

4. Projected Trends in the Effect of Global Warming on Human Health in the World

The projected trends of the effect of global warming on human health were also summarized in the fourth report of IPCC. 1 The projected trends in climate change-related effects include (1) increase in malnutrition and consequent disorders; (2) increase in the number of people suffering from death, disease, and injury from heat waves, floods, storms, fires, and droughts; (3) change of habitants of some infectious disease vectors; (4) mixed effects on malaria (the geographical range will contract in some areas, whereas it will expand and the transmission season may be changed); (5) increase in the burden of diarrhoeal diseases; (6) increase in cardiorespiratory morbidity and mortality associated with ground-level ozone; and (7) increase in the number of population at risk of dengue. On the other hand, there will be some benefits to health, including fewer deaths from cold. The benefits will be, however, outweighed by the negative effects of rising temperatures worldwide in developing countries.

The projected trends in the global warming effect in the East Asian countries may be different from those in other regions of the world. There will be increase in the number of heat shock cases and in increase in mortality rate among those who have cardiovascular and respiratory disorders, unless appropriate adaptation measures are taken. As stated above, there has not been apparent profound effect on infectious diseases in East Asia yet. It is predicted that the impacts will appear in one form or another if global warming continues to progress in future. Different from the projected trends in the developing counties, it is unlikely that global warming induce a great increase in the number of patients with diarrhoeal diseases in East Asian countries where social infrastructures are well established.

Furthermore, it is possible that activity of vector mosquitoes will become constantly high even in Northeast Asia. These trends, however, do not directly mean the increase in the number of patients with vector-borne infectious diseases, if appropriate countermeasures are taken.

5. Adaptation to the Global Warming

Even with the strongest mitigation measures, global warming cannot be avoided for decades. Therefore, implementation of adaptation procedures to the global warming is the most practical action we can take. There are multiple adaptation measures to the effect on infectious diseases. These include (1) vector control, (2) development of vaccines and implementation of vaccination, (3) development of new drugs, (4) establishment of surveillance and control programs, and (5) forecast of epidemic and development of preventive measures.

The impacts of global warming on infectious diseases have not been apparent at this point yet in East Asia. Research on the impacts of global warming on infectious diseases and future prospects in East Asia should be conducted in a wide range of research subjects.

In Conclusions, many studies have suggested that climate change has various negative effects on human health including infectious diseases. However, it should be noted that the levels of the impacts of climate change on human health will differ among regions, depending on various factors, such as social infrastructures, and establishment of countermeasures.

This makes the interpretation of the results of the studies quite difficult. Understanding of the effect of climate change on human health has been progressed very much in recent years; however, it is true that much more studies and data are needed to further understand in detail the effect of climate change.

There are other important issues to be considered especially in the study on the effect of infectious diseases. The number of patients with infectious diseases is affected by multiple factors. There are differences in virulence among strains in each pathogen. Thus, the number of symptomatic infection can vary depending on the level of the virulence of dominant strains of the pathogen. Furthermore, the changes in the number of cases depend heavily on the accuracy of surveillance and reporting systems, which are not still established in many developing countries. Thus, in the studies of the effect of global warming on infectious diseases, multiple biological, sociological, and economical factors should be taken into account.

Acknowledgements

This study was partially supported by the grants from Global Environment Research Fund by the Ministry of Environment, Japan (S-8) and from Research on Emerging and Re-emerging Infectious Diseases by the Ministry of Health, Labour and Welfare, Japan (H20-Shinkou-ippan-013).

Footnotes

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

References

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The Effect of Global Warming on Infectious Diseases

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Global warming has various effects on human health. The main indirect effects are on infectious diseases. Although the effects on infectious diseases will be detected worldwide, the degree and types of the effect are different, depending on the location ...

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Infectious agents vary greatly in size, type and mode of transmission. There are viruses, bacterias, protozoas and multicellularparasites. Those microbes that cause “anthroponoses” have adapted, via evolution, to the human species as their primary, usually exclusive, host. In contrast, non-human species are the natural reservoir for those infectious agents.