The Polar Retrospective – Pathogens increasingly affect polar wildlife
The Polar Retrospective looks back at events from the past week that are related to the Arctic and Antarctic and focuses on one or more aspects. This week, we look back to animal health in both polar regions as two studies focused on the impact of pathogens on polar bears while the avian flu is now emerging again as a discussion point in the awakening Antarctic regions and impacts human activities.
Despite the icy cold environment, animals in the Arctic and Antarctic regions always have been impacted by pathogens, no matter whether it’s a virus, bacteria or parasite. In fact, scientists consider these usually hardly visible organisms an essential factor driving the evolutionary development of animals. It always is an arms race between the immune system of the host and the measures of the pathogen to evade it and spread itself within the host. However, in recent decades, this system has been influenced by external environmental factors, usually tipping it in favor of the pathogen due to its faster adaption possibilities.
Two studies that were conducted in the Arctic and were published over the last couple of weeks provide further information that viruses, bacteria and parasites are on the move and thereby especially affect apex predators in the Arctic, the top one being polar bears. They also show that the health of polar bears other Arctic animals is not only a concern for the species itself but also for the Indigenous communities who rely on them for subsistence.
Pathogens increasingly trouble Chukchi Sea polar bears
A US study led by Dr. Kary D. Rode of the US Geological Survey and published in PLOS ONE recently looked at the increased pathogen exposure in polar bears in the Chukchi Sea region over a time span of thirty years. The research team revealed that the prevalence of antibodies to five pathogens such as Toxoplasma, Neospora and the canine distemper virus CDV significantly increased over the study period. The study identified several significant relationships between pathogen exposure and various factors. Notably, females exhibited higher seroprevalence for Francisella tularensis, Coxiella burnetii, and Brucella abortus/suis compared to males. Additionally, age also played a role, with the seroprevalence of Toxoplasma gondii and canine distemper virus (CDV) increasing with age.
One of the important drivers to this change in pathogen exposure seems to be a change in dietary habits, state the research team in their study. According to the results, switching the type of prey leads to an exposure to new pathogens as shown by bears that increased the consumption of bearded seals or bowhead whales instead of ringed seals, their preferred prey.
As a result, the exposure to new pathogens leads to an elevated immune response in polar bears according to the results of the study. This is a very costly investment, especially in summer, when high-energy food sources are harder to come by and polar bears need to manage their energy for hunt and subsistence.
More pollution, more impacted immune responses
Yet, polar bears are not the only animals that are affected by increased pathogen exposure. Another study, this time by an international team and published as pre-proof publication in the journal Science of the Total Environment, the authors provide compelling evidence that Arctic animals in general are increasingly affected by pathogens due to a combination of climate change, pollution, and ecological shifts.
While investigating the factors that drive this increased exposure and its impact, the authors found that high levels of persistent organic pollutants (POPs) and per- and polyfluoroalkyl substances (PFAS) in the Arctic environment lead to immune suppression in animals, making them more susceptible to infections. Again, looking at polar bears in different studies, the study led by authors Emilie Andersen-Ranberg from the University of Copenhagen and Dr. Christian Sonne from the Aarhus University showed that these predators have some of the highest concentrations of these pollutants globally, which exacerbates their vulnerability to diseases such as influenza and other viral infections.
These findings, however, do not contradict the findings of an elevated immune response as stated in the previous study from the US team as any infection usually leads to a response. It rather elicits that the response itself is not strong enough to get rid of the infection as it usually would in a non-polluted polar bear.
Zoonosis, an emerging problem in all polar regions
Another reason for more pathogen exposures is the transmission from newcomers to the polar regions to already established populations. The study by Andersen-Ranberg and her colleagues provide ample evidence for such transmissions, for example rabies from red foxes to Arctic foxes or the bacteria Erysipelothrix rhusiopathiae which usually is found among cattle but also caused widespread mortalities among musk oxen in 2015 in the Canadian Arctic. Again, the authors conclude that human-induced factors such as the warming of the Arctic and pollution support mass movements of non-Arctic species into the regions of the Far North.
Yet, such zoonoses are not restricted to the Arctic. Also, the Antarctic region is increasingly affected as last year’s avian flu outbreak in South America and South Georgia has clearly shown. There, mass mortalities among Southern elephant seals were recorded along the beaches in Argentina and Chile and was later found on South Georgia. Now recently, the authorities of the French Southern Territories reported a similar event on Possession Island, part of the Crozet archipelago. While the experts have only taken sample now to confirm the cause of deaths, the authorities already state that the outbreak is likely due to a “pathogen of influenza origin”.
While specific genetic evidence is yet missing, it seems likely that the elephant seals on Possession Island are also affected by the same virus as their counterparts on South Georgia and in Argentina. A study conducted by an international research team had revealed that the virus involved had been a mutation of the H5N1-HPAI virus allowing transmission from mammal to mammal.
Overall, these examples show that the challenges facing polar wildlife are complex and multifaceted. Climate change, pollution, and emerging diseases are all contributing to the vulnerability of these unique animals. Continued surveillance, research, and international collaboration are crucial to understanding and mitigating these threats. The recent outbreaks of avian influenza highlight the importance of biosecurity measures to prevent the spread of diseases. Protecting polar wildlife is not just a regional concern; it is a global imperative.
Dr. Michael Wenger, Polar Journal AG
Link to the studies:
E. Andersen-Ranberg, I.H. Nymo, P. Jokelainen, et al., Environmental stressors and zoonoses in the Arctic: Learning from the past to prepare for the future, Scie Tot Environ (2024)
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