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March 10, 2008

Infectious disease risk increases as a result of climate change

SickKids researchers anticipate increases in infectious disease in Canada

TORONTO - Scientists at The Hospital for Sick Children (SickKids) have published an article highlighting the potential impacts to human health, resulting from climate change. Infectious diseases, including those transmitted by insects and animals, fungal infections, water and food-borne illnesses, and disease transmitted from one person to another, are expected to increase in areas where the diseases are already present and will spread to new areas of the globe, including Canada. The article will be published in the March 11 th issue of the Canadian Medical Association Journal.

SickKids epidemiologist Dr. David Fisman, a scientist in the Child Health Evaluative Sciences program at SickKids Research Institute, and his colleagues Dr. Amy Greer and Victoria Ng, reviewed current data on changes to the environment and to weather patterns observed as a result of the warming of the earth's atmosphere, and related this to changes in the incidence and distribution of various types of infectious disease. Their review integrates data about disease dynamics, insects, the changing climate and ecosystems, and outlines some of the anticipated impacts on infectious disease incidence and burden in Canada .

Fisman, Greer and Ng predict that the biggest impact of temperature increases in Canada will be an expansion of the habitat range of disease-carrying insects such as ticks and mosquitoes. The range of these insects is anticipated to spread northward, along with the diseases they carry including Lyme disease and other coinfecting tick-borne diseases such as babesiosis (a malaria-like condition) , and anaplasmoses (a group of tick-borne blood diseases) . These types of infections present health risks to both humans and animals – Lyme disease, for example, can lead to cardiac and neurological infections as well as arthritic symptoms.

While ticks that spread Lyme disease are already present in southern Nova Scotia , Ontario , and British Columbia , shorter winters and higher temperatures will allow them to thrive in almost all populated regions of Canada . As well, early springs and longer summers will lead to a longer transmission season and an increase in disease incidence in mosquito-borne diseases such as West Nile .

The authors also anticipate that climate change will lead to higher numbers of water- and food-borne disease outbreaks in the Canadian population. Increases in precipitation, higher temperatures and flooding are linked to outbreaks of gastrointestinal and respiratory diseases caused by bacteria, protozoans and viruses – even in the presence of water-treatment facilities. Although Canadians have access to food and water that are remarkably safe by global standards, recent examples of large waterborne disease outbreaks in Canada include the 2000 Walkerton water disaster, and a 2001 outbreak of Cryptosporidium in North Battleford , Saskatchewan , that sickened over 6000 people. The confluence of increased flooding, heavy rains and warmer temperatures may make such events more frequent occurrences. Fisman, Greer and Ng advise that we will have to be even more vigilant to ensure the highest treatment standards in order to safeguard our water and food resources.

“An immediate impact of these changes is that physicians will need to have knowledge of these diseases and their symptoms, so that in the event a patient arrives with an unusual rash, an undiagnosed arthritis, or gastroenteritis, a correct diagnosis can be made and effective treatments prescribed,” stated Fisman. The paper noted that the impact of climate change on infectious diseases will be most severe in developing countries, where infectious diseases remain an important source of death in all age groups, and where infrastructure may not be sufficient to effectively treat or prevent spread.

A key objective of this paper is to urge policy makers and public health organizations to proactively prepare for these changes, by measuring and collecting baseline data on disease incidence in Canada and around the world. The authors suggest that by monitoring infections, the data collected will aid in anticipating and hopefully preventing outbreaks. While there are organizations around the world that are already starting to work towards this goal, including the Intergovernmental Panel on Climate Change (UN), the International Development Research Centre (Canada), and the World Health Organization Global Environmental Change Program, the authors stress the need for more cross-border collaborative approaches worldwide in order to protect populations against these threats.

Fisman and his team also emphasize the importance of multidisciplinary research in understanding and combating problems caused by climate change: “These changes highlight the relationships that exist between humans, insects, animals and the environment,” says Dr. Greer. “We need to reach beyond the traditional academic boundaries, to allow cross-disciplinary studies to be conducted between environmental scientists, health professionals, ecologists, geographers, as well as the veterinary community, because these new diseases may also impact livestock and wildlife populations.”

Innovative research in Fisman's lab is continuing to examine relationships between the environment and human health. Recent work has documented the importance of humidity, rainfall, ultraviolet radiation, and water conditions as factors that may cause the “seasonality” of infectious diseases (e.g., “cold and flu season”). In addition, they are investigating patterns between environmental conditions and reported outbreaks of gastroenteritis, in an effort to be able to better predict and prevent these from happening in the future.

Dr. Fisman acknowledges SickKids for allowing their group to pursue a non-traditional approach to studying human diseases. “We are glad to work in an institution that encourages us to break down the traditional research barriers and to follow the evidence to where it leads.” The researchers are also supported by the US National Institute of Allergy and Infectious Diseases, the Early Researcher Award Program of the Ontario Ministry of Research and Innovation, and SickKids Foundation.

 The Hospital for Sick Children (SickKids), affiliated with the University of Toronto, is Canada's most research-intensive hospital and the largest centre dedicated to improving children's health in the country. As innovators in child health, SickKids improves the health of children by integrating care, research and teaching. Our mission is to provide the best in complex and specialized care by creating scientific and clinical advancements, sharing our knowledge and expertise and championing the development of an accessible, comprehensive and sustainable child health system. For more information, please visit http://www.sickkids.ca/. SickKids is committed to healthier children for a better world.

For more information, please contact:

Janice Nicholson
Public Affairs
The Hospital for Sick Children
Phone: 416-813-6684
Fax: 416-813-5328
email: janice.nicholson@sickkids.ca