Insights about environmental change and emerging infectious disease have been derived primarily from temperate and tropical systems (1
), even though host–pathogen relationships at higher latitudes of the Northern Hemisphere are affected by rapid climate change and anthropogenic disturbance (4
). The North, therefore, serves as a sentinel and a complementary window, relative to temperate and tropical environments, for assessing the cascading ecologic effects of global climate change. Within relatively simple northern ecosystems, it is possible to differentiate signals of climate change from those associated with nonclimatologic drivers. Consequently, the North is a vital frontier for the exploration of biotic, abiotic, and historical determinants that influence the distribution, host associations, and evolution of pathogens in wildlife and human populations (4
Host–parasite systems are particularly sensitive indicators of climate change and other causes of ecologic perturbation (3
). Many macroparasites (e.g., helminths and arthropods) undergo life cycles with free-living stages whose development and survival are influenced by temperature, among other abiotic factors (2
). For example, small changes in absolute temperatures can have substantial effects on the transmission dynamics of protostrongylid lungworms and muscleworms (species of Parelaphostrongylus
, and Umingmakstrongylus
), which cycle among the environment, gastropod (slug and snail) intermediate hosts, and ungulate (caribou, muskoxen, thinhorn sheep, moose) definitive hosts (). These parasites are pathogenic in wildlife important to northern communities for cultural, economic, and spiritual reasons (4
). The importance of keystone wildlife (those critical for the function and continuity of ecosystems and northern peoples), the potential sensitivity of host–pathogen assemblages to environmental disturbance, and the present and predicted scale of accelerated climate change and cascading ecologic effects in the North give urgency to the need for a better understanding of these systems now and in the future. These environmental changes may presage substantial consequences for health, economic well-being, and continuity of culture and society at a global level.
Figure 1 Life cycle of protostrongylid parasite: Umingmakstrongylus pallikuukensis in muskoxen definitive and gastropod intermediate hosts (12). Adult nematodes (for U. pallikuukensis, located in the lungs) lay eggs, which hatch to first-stage larvae (L1). L1 (more ...)
The current International Polar Year, which covers the period March 2007 to March 2009 (although officially designated International Polar Year 2007–2008), offers a unique opportunity to develop a baseline, or snapshot, of the North and to explore the patterns and processes for infectious disease emergence in northern ecosystems that are globally relevant. As a contribution to this baseline, we outline approaches, protocols, and empirical models derived from a decade of exploration of pathogen biodiversity and disease in northern ecosystems (), illustrated with examples of drivers for emerging parasitic disease in northern wildlife (). Categories of emergence explored in our studies include 1) geographic expansion, 2) host switching, 3) resurgence due to climate change, 4) new introduction, and 5) new recognition of pathogens. This approach can be viewed as a broadly applicable framework for defining pathogen diversity, including distinguishing what is truly emerging from what is newly discovered, and the historical and contemporary drivers associated with emerging infectious diseases in the North and elsewhere in the world. This ecologic approach to understanding disease emergence in wildlife complements a growing recognition of the need for long-term epidemiologic datasets to detect the effects of climate change on human health (8
). Collectively, these constitute a critical sentinel for the interaction of climate and infectious disease in the global arena.
Approaches and tools for exploring diversity and changes in complex host-parasite systems
Responses to climate warming and drivers for emergence of parasites and parasitic diseases in Arctic systems