Arctic Warming Increases Polar Bears’ Risk of New Diseases

As the Arctic warms at an alarming rate, melting ice is redefining the boundaries of polar bear habitat. Faced with increasingly long periods spent on dry land, these emblematic predators of the sea ice now find themselves exposed to pathogens formerly foreign to their environment. This forced movement to land areas has unexpected consequences: new diseases are beginning to emerge, directly threatening the health of these majestic carnivores, and potentially that of the entire Arctic ecosystem.

The impact of global warming on the health of polar bears

Global warming is radically transforming the Arctic ecosystem, putting polar bears in contact with pathogens that they were less likely to encounter just thirty years ago.

A study published in PLOS One, relayed by the BBC, reveals that the rapid melting of the sea ice has forced bears to spend more time on dry land, thus exposing them to viruses, bacteria and parasites associated with terrestrial species.

Between 1987 and 1994, blood samples were collected from polar bears living in the Chukchi Sea, a region between Alaska and Russia. The researchers compared these samples with those collected between 2008 and 2017.

The results show a significant increase in the presence of antibodies linked to five pathogens: Toxoplasma gondii, responsible for toxoplasmosis, Neospora caninum, Francisella tularensis (cause of tularemia or “rabbit fever”), Brucella abortus/ suis (responsible for brucellosis), and the canine distemper virus.

Polar bears, top predators in the Arctic food chain, now face increased exposure to these pathogens. This exposure results from their increased use of land during the summer, when sea ice disappears. This change in habitat directly affects their health, but also that of other local species.

Changes in food interactions and population risks

Changes in polar bear habitat also lead to changes in their diet. Studies based on the analysis of isotopes in the hair of polar bears have revealed that their diet varies depending on their exposure to pathogens.

For example, bears exposed to Toxoplasma gondii consumed more bearded seals. On the other hand, those affected by Francisella tularensis ate fewer young ringed seals.

Researchers also observed higher exposure in females. This is probably explained by their habit of staying on land longer during giving birth and caring for the young.

This greater exposure to terrestrial pathogens seems linked to their reproductive behavior. Females are more likely to come into contact with parasites and bacteria in their environment.

Blood tests show a significant increase in antibodies against these pathogens over the past three decades. For example, antibodies linked to tularemia and Toxoplasma gondii more than doubled between the periods studied.

These results suggest that disease transmission in the Arctic ecosystem is evolving rapidly. However, the consequences on the overall health of polar bears remain poorly understood.

Implications for human communities and Arctic wildlife

The increase in the presence of pathogens in the Arctic environment is not limited to polar bears. Some of the diseases identified, such as brucellosis and toxoplasmosis, are zoonotic, meaning they can be transmitted to humans.

Local communities, who sometimes hunt polar bears for their meat, are thus exposed to these health risks. In addition, the risk of pathogen transmission to other Arctic species, such as seals or foxes, increases. This situation could upset the fragile balance of the Arctic ecosystem.

Scientists point out that these changes in disease dynamics are linked to the disappearance of sea ice. By spending more time on land, polar bears interact differently with other species, exposing them to new dangers.

Although studies show that the physical condition and reproductive rate of Chukchi Sea bears are stable, monitoring is still necessary. Understanding the long-term impact of these changes on their health and survival is essential for their preservation.

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