Disease
As temperatures rise, the active season of parasites that infect caribou and reindeer is lengthening, and the ranges of these species are also expanding northward further and further into the Arctic.
Parasite Active Season
Parasitic insects such as warble flies and nose botflies harass Arctic caribou and reindeer during the summer. These parasites can disrupt behavior by forcing herds to travel long distances and behave erratically to escape harassment, reducing time spent foraging and increasing energy expenditure, Warmer temperatures are expected to cause increases in the time that these parasites are active, negatively affecting body condition and reproduction (Mallory & Boyce, 2017).
The nematode Elaphostrongylus rangiferi is a common parasite of reindeer in northern Fennoscandinavia, Russia, and Canada. Reindeer can consume the parasite when they eat gastropods hosting the larvae. The nematode can cause pneumonia and neurological symptoms such as paralysis of the hindquarters. The abundance of infection with the nematode in reindeer increases as summer temperature increases, possibly due to the parasite's temperature-dependent developmental rate or changes in the movement of gastropods on vegetation increasing their likelihood of consumption by reindeer (Halvorsen, 2012).
Parasite Range Expansion
Varestrongylus eleguneniensis is a lungworm that infects caribou in the Canadian Arctic. The range of the lungworm has been expanding northward in recent years, likely because larval development rate of the lungworm inside an intermediate host is positively correlated with temperature. As temperatures warm due to climate change, increased expansion of V. eleguneniensis into the Arctic poses a rising threat for caribou populations (Kafle, et al., 2018).
Kafle, et al., 2018
Anthrax, a bacterial disease that infects livestock and humans, is also expected to expand as temperatures rise. Anthrax spores remain dormant in the ground until they are consumed by ungulates during grazing. Direct contact with infected animals or consumption of undercooked meat of infected livestock can cause the disease to spread to humans. Anthrax suitability increases drastically in regions where temperatures are rising anomalously, occurring most notably in the Arctic. Melting permafrost may expose ungulate carcasses and thaw frozen tissues and body fluids, releasing spores. Furthermore, changing migration routes of indigenous reindeer herding communities and wild caribou herds due to shifting patterns of ice and open water may make Rangifer populations and the humans that depend on them more susceptible to the disease, especially as it continues to expand northward. Environmental conditions appear to be most optimal for anthrax in northern Siberia, Iceland, and Scandinavia, as well as in the high Arctic regions of North America. As climate change progresses, anthrax suitability is expected to increase across the globe, as well as in the Arctic (Walsh, et al., 2018).
Walsh, et al., 2018
The Arctic is especially vulnerable to parasitic invasions due to expanding ranges because of its low biodiversity. For instance, researchers observed that environmental suitability for anthrax decreased as ungulate species richness increased (Walsh, et al., 2018). Additionally, species adapted to the cold environment may be unable to compete with new parasitic species as temperatures rise (Mallory & Boyce, 2017).
Walsh, et al., 2018