Infections on the move
14 April 2020
In the Arctic, changes in the environment can alter how infection-causing agents survive, thrive and infect humans and animals. Tick-borne diseases, for example, are some of the most researched infections associated with climate change because temperature and precipitation affect the tick’s lifecycle and habitat—along with those of their host animals.
Creating the perfect environment for ticks
As Arctic temperatures warm, the boreal tree line and tundra are moving further north, creating new habitat opportunities for ticks. Some will carry diseases with them, such as tick-borne encephalitis (TBE) or tick-borne borreliosis. The warmer temperatures can also speed up ticks’ development and reproduction, resulting in larger populations.
As these ticks move further north, they will come into contact with more wildlife and humans, increasing the number of animals with the potential to carry disease—and along with that, the risk of infection.
In Europe and Russia, Ixodes ricinus and Ixodes persulcatus ticks are responsible for most TBE infections. Researchers have observed that these ticks are already expanding their range north. In Sweden, for example, the Ixodes ricinus tick range has grown by 10 per cent, with most of the expansion occurring above the Arctic Circle. This could lead to more animals becoming hosts in the ticks’ life cycles, and possibly to an increase in TBE cases.
Posing a new threat to Arctic animals and humans
In humans, TBE begins with nonspecific symptoms (such as fever, headache and nausea) and can progress to more severe neurologic symptoms. In rare cases, it can be fatal.
Ticks rely on large mammals of the deer family (cervids)—for example, red deer, roe deer or moose—for nutrition, and can be found in large numbers on these animals. Antibodies to the TBE virus—an indicator of previous TBE infection—have been found in cervids. However, TBE does not usually cause symptoms in these mammals.
Data suggest that climate factors like warmer temperatures, milder winters, earlier spring arrivals and the population of the ticks’ animal hosts correlate with TBE cases in humans.
Preventing the spread of infection
Because climate change is a complex problem occurring simultaneously with globalisation, it is not the only factor contributing to the changes we are seeing in infection rates. However, monitoring tick populations and the climate factors that influence the populations involved, and monitoring TBE infections in Arctic wildlife, can be crucial for predicting TBE cases in humans.
While the changing environment and increased migration to the Arctic may increase the risk of some infections, there are ways to prevent their spread. Vaccination programmes are one example. Another is education for health care personnel and the public about climate-sensitive infections. We can also use international infection surveillance of both human and animal cases to track how diseases are spreading and help mitigate the effects of climate change on infectious diseases for people living in the Arctic.
AUDREY WAITS is a researcher at the University of Oulu in Finland. She focuses on how climate change is expected to affect human and wildlife health in the Arctic.
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