Anticipating, Preventing, and Mitigating Climate Change Impacts on Host-Parasite Interactions by using the Arctic as a Model

Increase in global temperature has strongly affected the Arctic. It has shrunk the sea ice extent, decreased the size of mountain glaciers and amount of snowmelt, as well as reduced the maximum areal extent of seasonally frozen ground. This temperature change will also have profound effects on pathogens. Climate is an important factor in determining the diversity and abundance of pathogens as well as the patterns of disease they cause. The prediction for pathogens in a warmer climate is for increased transmission rates, longer periods for transmission, and shifts in spatial and temporal patterns of pathogen diversity and associated disease. Kut et al. (2009) use the findings and developments of previous case studies to promote wildlife conservation, ecosystem health, and human health. To do so they identify and address knowledge gaps, develop conceptual and predictive tools, establish efficient monitoring and early detection programs, and focus on evidence-based approaches to prevention and mitigation. Clara Lyashevsky
Kutz, S., Jenkins, E., Veitch, A., Ducrocq, J., Polley, L., Elkin, B., Liar, S., 2009. The Arctic as a model for anticipating, preventing, and mitigating climate change impacts on host—parasite interactions. Vet. Parasitology 163, 217–228.

The Arctic is a relatively simple system for examining the effects of climate change on infectious disease in wildlife. Climate change is occurring at an unprecedented rate in the North and observable physical and biological responses are happening in real time. The Arctic also has low biological diversity and, consequently, is vulnerable to invasions and as a result, it will respond rapidly and measurably to environmental disturbances.
Parasites and other pathogens are known to influence wildlife at the individual and population levels. Hunters in the Canadian Arctic and Subarctic informed researchers of the unusual numbersof sick caribou with poor coats and ulcerated limbs, which catalyzed research on Umingmakstrongylus pallikuukensis, a protostrongylid lungworm of muskoxen. The adult nematodes of this lungworm reside in cysts in the lungs of muskoxen and deposit their eggs into them. The eggs then hatch to first stage larvae, move up the airways, they are then swallowed and passed through the gastrointestinal tract, and deposited in feces. The larvae then invade gastropod intermediate hosts (IHs) and develop into the infective third stage.
Empirical field and laboratory data were used to construct predictive models for the development rates of larvae of U. pallikuukensis in IHs. The models are based on degree day calculations and incorporate soil surface temperatures as well as the behavior of the gastropod intermediate hosts. An upper threshold of 21 oC is incorporated into the model; it is assumed that the parasite is maintained at that temperature. U. pallikuukenis take 2 years to develop into the infective third stage, meaning that the developing larvae and the IHs would have to survive winter in order to complete the parasite’s lifecycle. The model suggests that the increase in temperatures hastens larval development, and the infective stage is reached within a single summer. Increases in temperature and a longer summer transmission window could potentially result in the increase of infective larvae available to the muskoxen. As a result, climate change is expected to lead to a net increase in infective larvae, increase infection, and to expand the area in which temperatures are sufficient for larval development.
It was also found that the winter tick, Dermacentor albipictus, is expanding its geographic range in the Canadian North. Winter ticks are host ticks that moult from larvae to adults on a single infected host throughout the winter. Adult ticks mate on the host and lay eggs in the spring. The eggs hatch during the summer and then larval ticks look for a new host that autumn. Therefore the climates of spring, summer, and autumn are critical for the development of the tick. Any change in climate alters their maturation.
There are no baseline data on parasite diversity, life cycles, and effects, which makes understanding the effect of climate difficult. Molecular tools can be applied to fecal stages for noninvasive sampling and accurate identifications to simplify these investigations. How the parasite affects the host helps evaluate the importance of potential changes in a specific host-parasite interaction. In order to better understand host-parasite interactions, researchers use cross-sectional studies. Experimental infections can be critical in defining the susceptibility of host species at risk of infection with a ‘new’ parasite.
The authors concluded that the effects of climate change are not uniform across host or parasite. Increase in temperature will facilitate invasion of new parasites. For example, parasites that previously could not develop in northern ecosystems may soon be able to with climate warming. Also, the invasion of new hosts may alter ecosystems by introduction of new parasites as well as by changing the abundance and distribution of endemic parasite species.

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