Potential Impacts of Global Warming and Climate Change on the Epidemiology of Zoonotic Diseases in Canada
Charron, Dominique F., Canadian Journal of Public Health
Global climate change may add to the risk of infectious diseases faced by Canadians. A warmer climate may permit the northward expansion of certain disease reservoir animal hosts and vectors increasing the risk to Canadians from zoonotic diseases, i.e., diseases that are transmissible between animals and humans. A shorter, less severe winter would prolong the transmission season for many existing Canadian zoonoses, and could allow previously exotic zoonoses that enter Canada to become established. Significant challenges to epidemiological forecasting arise from complex interactions among climatic factors, zoonotic disease agents, other infectious agents, underlying human health and immunity, socio-economic factors, and ecological parameters. Public health officials and health care providers need to be kept informed of the changing nature of zoonotic disease risk in order to be vigilant in the early detection of disease, and to plan to respond to new or increased health risks. Surveillance and public education will also help protect Canadians from any additional zoonotic health risks of climate change.
Global warming and climate change
Global warming and associated climate change will be important determinants of future Canadian public health.1 The International Panel on Climate Change (IPCC) accepts projections of a 1.4 to 5.8(deg)C increase in mean global temperature by 2100 as a result of the accumulation of greenhouse gases (carbon dioxide, ozone, methane, nitrous oxide, and water vapour) in the atmosphere. Achievement of Kyoto emissions reduction targets will reduce the rate of warming but will not prevent it.2 Climate changes in Canada may include increased temperature over most of Canada, especially in winter and at night; reduced soil moisture and summer drought; increased frequency of extreme precipitation events; more severe weather; and an 11 to 77 cm sea-level rise, by 2100.(2) The greatest changes may affect the Arctic.2,3
Climate change may increase the risk to Canadians from vectorborne diseases (caused by pathogens with an invertebrate vector), including arboviral encephalitis, rickettsial diseases, and Lyme borreliosis. Forecasts under conditions of global warming suggest an increase in arboviral encephalitis in the US.4 Increased temperatures and longer summers may extend the survival of vectors in Canada, and allow the northward expansion of the ranges of other vectors.5 Sporadic human cases of arboviral encephalitis in Canada have been caused by Western Equine Encephalitis (WEE), Powassan virus and viruses of the California serogroup (including Snowshoe Hare virus). There have also been outbreaks of Eastern Equine Encephalitis (EEE) in horses.6,7 Outbreaks of St. Louis Encephalitis (SLE) are common in the US8 and there are American reports of sporadic outbreaks of others, including West Nile Virus (WNV).9 West Nile Virus has been found in bird carcasses from southern Ontario.10
Rocky Mountain Spotted fever,9 Lyme borreliosis,11,12 and ehrlichiosis13 are tick-- borne diseases that may have increased incidence in Canada given milder winters and increased spring precipitation. Warmer temperatures could accelerate pathogen development within the tick,12 and populations of reservoir mice and deer could expand due to increased food availability and decreased winter die-off. Longer summers might increase the risk of human recreational exposure.
Foodborne and waterborne zoonoses
Every year in Canada, foodborne infections cause significant morbidity and mortality.14 Many, including Salmonella and Escherichia coli 0157:H7, have known food animal or wildlife reservoirs. 14-17 Climate change has been tentatively linked to increased foodborne disease incidence in the UK.18 Elevated temperatures in North America may exacerbate food contamination during livestock rearing, food processing, and food preparation. Outbreaks of zoonotic diarrhea in heat-stressed livestock may contribute to this contamination. …