Climate Change: Preparing for the Health Impacts

Signs of Change, Signs of Trouble: Finding the Evidence

Dominique Charron, D.V.M, Ph.D., and Paul Sockett, Centre for Infectious Disease Prevention and Control, Public Health Agency of Canada

Given the diverse pathways by which climate change affects health, many sources of evidence are required to assess the potential or actual impacts of climate change on health. While public health professionals monitor Canadian population health trends through disease surveillance activities, researchers measure the links between health outcomes and changes in weather or climate, and model how climate change may alter patterns of health and disease. Surveillance is also helping public health authorities anticipate the climate-related spread of vector-borne diseases like Lyme disease by tracking geographic shifts in the distribution of ticks carrying the disease.

Surveillance Data: Covering All the Bases

To detect and effectively assess the health impacts of climate change and climate variability, it is important to recognize the various ways by which climate can affect health (e.g., direct stress from temperature extremes, impacts of poor air quality episodes, more favourable conditions for waterborne and vector-borne diseases). Timely, accurate and reliable health surveillance data are key to detecting changes in disease patterns over time and between different populations, including changes that may result from the combined ecological and societal impacts of climate change. A key public health challenge is to understand the causes of these disease patterns and then to implement programs that reduce the burden of illness.

Comprehensive Disease Tracking Systems

Effective disease surveillance requires a variety of activities and the involvement of health authorities at all levels. As Figure 1 illustrates, local, provincial and federal health departments are all active participants in surveillance. Each maintains registries of health data on certain diseases, infections, hospitalizations and injuries, while the World Health Organization (WHO) monitors similar data at a global level. These data, collected by recording events as they occur, contribute to passive surveillance and may be enhanced by active surveillance programs that obtain data on particular health problems (e.g., emerging infections).¹ For example, during a recent Montréal heat wave, health outcomes of the older population were monitored as part of the city's Heat Wave Mobilization Plan.

Figure 1: Effective Surveillance

Looking in Unexpected Places

A number of alternate surveillance activities augment the information obtained from tracking individual cases of disease. These include monitoring zoonotic diseases (diseases transmissible between animals and people) in reservoir animal populations. For example, Canadian public health authorities routinely monitor West Nile virus activity in birds and mosquitoes to measure the human health risk ( http://www.phac-aspc.gc.ca/wn-no/surveillance-eng.php). Research is also under way to understand how trends in over-the-counter medication (e.g., anti-diarrheal remedies) may help detect waterborne illness in communities where flooding has been a concern.² As discussed in the article on page 41, newspapers have also been useful in monitoring health problems related to extreme weather events.³ The importance of alternative systems such as these is likely to increase as we face global environmental change in times of competing demands on limited resources.

Local Communities Play a Role

Local communities may also contribute helpful information often not captured by health surveillance activities alone. Sources such as these are especially important when studying the impacts of weather and climate on health. For example, First Nations elders may contribute pertinent observations on changes taking place in their communities and environments.⁴ Farmers may understand the significance of weather patterns and can provide useful insights regarding health impacts. Similarly, hunters and fishers may observe changes in the health of wildlife that represent a human health risk.⁵

Linking Weather to Health

For specific information on health risks associated with climate and weather, public health professionals depend on research findings about the links between health outcomes and various health determinants, including climate and weather. Canadian researchers are increasingly active in this area and use meteorological records, climate models and data on many environmental and social health determinants to understand how some health problems may be vulnerable to changes in weather and, eventually, to the impacts of climate change. The following study, funded by Health Canada's Health Policy Research Program, found that heavy rainfall was linked to increased risk of waterborne disease.

Heavy Rain and Waterborne Disease

The Public Health Agency of Canada (PHAC) collaborated with the University of Guelph and Environment Canada on an analysis of historical outbreaks of disease linked to a source of drinking water. Preliminary findings indicate that warmer temperatures and very heavy rainfall tend to increase the risk of disease outbreaks within a six-week period.⁶ As shown in Figure 2, only the heaviest rainfall periods contributed to increased risk of waterborne disease. Warmer temperatures also contributed to an increased outbreak risk.

The findings suggest that warmer temperatures and extreme rainfall are contributing factors to waterborne disease outbreaks in Canada. Given that warmer temperatures and more extreme precipitation are projected under many climate change scenarios, decision makers and planners should consider watershed protection measures and increasing safety barriers to protect drinking water from extreme rainfall.

Figure 2: Link between Rainfall and Waterborne Disease Outbreak

Source: D.F. Charron et al., 2004. ⁶

Modelling the Health Impacts of Climate Change

Knowing how certain health problems are influenced by weather is vital. However, it is also important to use this knowledge to anticipate and predict future health risks posed by a changing climate. As the following study demonstrates, new disease modelling techniques that project the impacts of climate change on Canadian health issues are becoming valued public health tools.

Figure 3: Ixodes Scapularis - Current and Projected Ranges in Canada

Note: future limits are model-derived temperature limits mapped as limits in mean annual degree-days >0°C. Climate change projections wereobtained from output from the CGCM2 global climate model using IPCC emissions scenario "A2."
Source: Adapted with permission from Elsevier from N.H. Ogden et al., Climate change and the potential for range expansion of the Lyme disease vector Ixodes scapularis in Canada, International Journal of Parasitology, 2005 (in press).

Mapping the Spread of Vector-Borne Diseases

The geographic range of many vector-borne diseases is limited by climate conditions.^{7, 8, 9, 10} A case in point is Lyme disease, which is caused by a bacterial infection transmitted by black-legged ticks in certain regions of Canada. Research funded by the Climate Change Action Fund of the Government of Canada has shown that vector tick distribution east of the Rockies is confined by climate and habitat. However, a changing climate could extend the tick's range, thereby exposing more Canadians to Lyme disease.

Lyme disease infects about 20,000 people a year in the United States.¹¹ Fewer than 50 cases are diagnosed annually by laboratory in Canada (Approximately half of the cases diagnosed by laboratory are linked to travel to areas outside of Canada where Lyme disease is very common.), but many more are treated for Lyme disease based on symptoms and history alone. Lyme disease ecology differs from region to region across Canada. The current northern limit of the vector tick Ix. scapularis is southern Ontario, with a few isolated tick populations on the shores of Lakes Erie and Ontario, and one population on the south coast of Nova Scotia.¹² The western black-legged tick, Ix. Pacificus, is found throughout British Columbia,¹³ but because this tick prefers reptilian hosts that do not harbour the Lyme disease bacteria, the disease is not as easily spread to humans.

Due to projected climate change, a northward shift in range is expected for many arthropods such as ticks.^14,15 Figure 3 illustrates the northward shift in range expected for Ix. scapularis. Established populations and present-day limits of the tick's geographic range (using 1971-2000 data) are shown, along with projected future geographic ranges of temperature conditions suitable for the tick to become established.

If the range of Ix. scapularis expands northward, it will extend into parts of southeastern Canada that are densely populated, with consequent risks for public health. Such an expansion is considered likely in the face of climate change for the following reasons:

• Some areas of the United States most severely affected by Lyme disease border on Québec, Ontario and the Maritimes. Migrating birds carry infected ticks into Canada from these areas.
• These same areas in southeastern Canada already provide a habitat for mice and white-tailed deer, which are animal hosts to Ixodes ticks. The ticks are also able to survive in these areas when off their animal hosts.
• At the northern edge of its range, Ix. scapularis survival is closely controlled by temperature.^10,12

Short- and Long-Term Health Challenges

Climate variability and change have impacts on a broad spectrum of health determinants and, consequently, far-reaching impacts on society. For this reason, public health professionals and health care providers will need to be alert to the indirect as well as the direct impacts of climate change. For example, while warmer and drier summer conditions in the Canadian Prairies might not result in an increased number of heat-related deaths, attention must be paid to the more subtle and long-term health effects of drought. Drinking water supplies may be threatened. Crop failure and loss of farmland from soil salinity may have enormous economic implications for farm families and rural communities, with repercussions on overall nutrition, child health and mental health. This, in turn, may result in an increasing incidence of suicide and family violence, injuries and chronic diseases.

Moving Forward

Climate change poses complex short- and long-term public health challenges. It requires that health professionals from all disciplines take a broader, more systemic view of the possible linkages and trends between health determinants and health outcomes, as well as the linkages between human health and the health of our natural and built environments. The diverse pathways through which climate change affects health underscores how human health and well-being are intricately linked to the health of the ecosystems in which we live.

In Canada, disease surveillance has moved from the traditional work of recording past events to a more active, anticipatory activity designed to identify health threats as early as possible. To be effective, such an approach requires a collaborative effort among health professionals and their allies at all levels of government, as well as internationally. Currently, the Public Health Agency of Canada (PHAC) is working with provincial and territorial ministries and agencies to conduct health surveillance. PHAC is also leading important research on how climate change may affect Canadians' risk of infectious diseases. Together with Health Canada, the Agency is fostering partnerships with other federal departments to determine the impacts of climate change on the broader determinants of health and to better identify the risks posed by climate change.

Myth?

Climate change may cause malaria to re-emerge in Canada.

True

There is considerable uncertainty about how climate change will affect the vector life cycle and disease incidence of malaria in North America. Climate change is only one of a number of factors that can affect the spread of malaria; increased travel and immigration, and increased drug resistance are some of the other causes. People infected with malaria who are exposed to North American mosquitoes capable of transmitting the Plasmodium parasite can cause local outbreaks.⁵ As well, new insect vectors introduced to North America from other countries and capable of spreading the parasite may extend their range to Canada if climatic conditions become more favourable. However, Canada's public health infrastructure minimizes the threat of disease spreading beyond a local outbreak.

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Issue 11 References

References for Signs of Change, Signs of Trouble: Finding the Evidence

1. Pinner, R.W., Rebmann, C.A., Schuchat, A., & Hughes, J.M. (2003). Disease surveillance and the academic, clinical, and public health communities. Emerging Infectious Disease Journal, 9(7), 781-787.

2. Edge, V.L., Pollari, F., Lim, G., Aramini, J., Sockett, P., Martin, S.W., et al. (2004). Syndromic surveillance of gastrointestinal illness using pharmacy over-the-counter sales. A retrospective study of waterborne outbreaks in Saskatchewan and Ontario. Canadian Journal of Public Health, 95(6), 446-450.

3. Soskolne, C.L., Smoyer-Tomic, K.E., Spady, D.W., McDonald, K., Rothe, J.P., & Klaver, J.D.A. (2004, April 30). Final Report: Climate Change, Extreme Weather Events and Health Effects in Alberta. HPRP File No. 6795-15-2001/4400013. Ottawa, ON: Health Canada.

4. MacKinnon, M. (2005). A First Nations voice in the present creates healing in the future. Canadian Journal of Public Health, 96 Suppl. 1, S13-S16.

5. Sang, S., Booth, C., & Balch, G. (2004). Documentation of Inuit Qaujimajatuqangit (local knowledge) in Pangnirtung, Coral Harbour and Arviat, Nunavut: Nunavut Wildlife Health Assessment Project. (PDF version) © World Wildlife Fund Canada and Trent University, Canada. Retrieved from
< http://wwf.ca/Documents/Arctic/nwha_eng_sp.pdf>.

6. Charron, D.F., et al. (2004). The Role of High Impact Weather in Waterborne Disease Outbreaks in Canada, 1975-2001. Submitted to International Journal of Environmental and Occupational Health.

7. Alto, B.W., & Juliano, S.A. (2001). Precipitation and temperature effects on populations of Aedes albopictus (Diptera: Culicidae): implications for range expansion. Journal of Medical Entomology, 38(5), 646-656.

8. Reiter, P. (2001). Climate change and mosquito-borne disease. Environmental Health Perspectives, 109 Suppl. 1, 141-161.

9. Brownstein, J.S., Holford, T.R., & Fish, D. (2003). A climate-based model predicts the spatial distribution of the Lyme disease vector Ixodes scapularis in the United States. Environmental Health Perspectives, 111(9), 1152-1157.

10. Ogden, N.H., Lindsay, L.R., Charron, D., Beauchamp, G., Maarouf, A., O'Callaghan, C.J., et al. (2004). Investigation of the relationships between temperature and development rates of the tick Ixodes scapularis (Acari: Ixodidae) in the laboratory and field. Journal of Medical Entomology, 41, 622-633.

11. Centers for Disease Control. (2003). Notice to Readers: Final 2002 Reports of Notifiable Diseases. Morbidity and Mortality Weekly Report, 5(31), 741-750.

12. Ogden, N.H., Bigras-Poulin, M., Barker, I.K., Lindsay, L.R., Maarouf, A., O'Callaghan, C.J., et al. (2005). A dynamic population model to investigate effects of climate on geographic range and seasonality of the tick Ixodes scapularis. International Journal of Parasitology, 35, 375-389.

13. Morshed, M. (2005). Personal communication. British Columbia Centre for Disease Control.

14. Parmesan, C., & Yohe, G. (2003). A globally coherent fingerprint of climate change impacts across natural systems. Nature, 421, 37-42.

15. Ogden, N.H., Barker, I.K., Lindsay, L.R., Maarouf, A., O'Callaghan, C.J., Waltner-Toews, D., et al. (2005). Survival of Ixodes scapularis ticks in habitats of South Eastern Canada: field study and modelling analysis. In prep.

References for Did you know? Myths

5. Bradley, C.B., et al. (2000). Probable locally acquired mosquito-transmitted Plasmodium vivax infection, Suffolk County, New York, 1999. Morbidity and Mortality Weekly Report, 49(22), 495-498.