ABSTRACT
Rangifer populations globally are host to a variety of infectious agents including viruses, bacteria, helminths (worms), protozoa and arthropods (see Chapters 6–9 for more details). Infectious agents are not only incredibly common, they are also an integral part of ecosystems with population and community level effects. They can interact with other ecological drivers, resulting in both detrimental and beneficial effects on ecosystem health and biodiversity (Gómez and Nichols 2013). Highly pathogenic agents, or those invading naïve populations, can have obvious and dramatic consequences for the dynamics and abundance of their host species. For example, the fungal disease white-nose syndrome has killed more than five million bats in North America, and chytrid fungus has wiped out amphibians in regions around the world. They can also have other and further reaching consequences, such as the recent 2016 anthrax outbreak in reindeer in Russia. The outbreak had social, economic and ecological consequences; 2,300 reindeer died, with significant economic loss for reindeer herders, who were also moved out of the area due to the zoonotic potential of the disease, which one boy succumbed to. Impacts of infectious agents may also be more subtle, where they negatively affect hosts without causing overt disease. Yet, they may still influence birth and death rates of individuals and, thereby, influence population dynamics. Subtle impacts may only become noticeable in certain contexts, such as in conjunction with other stressors, such as severe weather, poor habitat, predation and other infectious agents. Through these interacting and subtle effects, pathogens that initially appear less virulent may have equally important impacts on host fitness (reproduction and/or survival) and population dynamics as more virulent pathogens.
