Beaver’s role in the spread of tularemia investigated: No increased risk found
Beaver dams have sometimes been identified as potential hotspots for pathogens and the spread of animal-borne diseases such as tularemia. But a new thesis from SLU clears the Swedish beavers of these suspicions. Beaver ponds do not pose a greater risk of disease transmission than other wetlands.
– Beavers build dams and create wetlands that promote biodiversity, but these same environments can also favour the spread of zoonotic diseases. Having now investigated and assessed the risks, we can see that beavers in Sweden do not appear to cause an increased spread of infection, says Lovisa Hökby, a PhD student at SLU and the author of the thesis.
One of the pathogens she has examined is the tularemia bacterium. It can be transmitted to humans via mosquitoes, which are often abundant in stagnant water and ponds. Whilst working on her thesis, Lovisa Hökby collected water samples from both beaver dams and other wetlands in Sweden. The water samples, along with tissue and faeces from beavers, were then tested for a total of 21 different infectious agents, known as pathogens. These included the bacterium that can cause tularemia.
– The results show that pathogens occurred at similar prevalences in wetlands regardless of whether there were beavers there or not. Nor do the beavers themselves appear to play a central role as host animals. Most of the beavers we examined tested negative for all pathogens, says Lovisa Hökby.
Infected hares in areas with water
Many small rodents and hares are thought to be important hosts for tularemia. When Lovisa Hökby studied data on areas where dead hares had been found and tested for tularemia, she noticed a pattern. The infected hares could be linked to wetter environments.
– The conclusion is that the presence of water in the landscape increases the risk of infection in hares. One possible explanation is that the hares have also been infected by mosquitoes, says Lovisa Hökby.
In some years, there are major outbreaks of tularemia and many people fall ill. There are still gaps in our understanding of the factors behind these peak years, but the findings from the thesis on beavers add another piece to the puzzle.
Reinforces the beaver’s role as a conservationist
According to the researchers, climate change and disrupted ecosystems pose a risk and that humans will be exposed to more zoonotic diseases in the future. A disrupted balance can favour disease-carrying animals. High biodiversity, on the other hand, often helps to reduce the proportion of infected animals, and the environments where beavers build their dams are rich in species diversity. For example, these areas often support species that feed on mosquito larvae, which can reduce the spread of diseases transmitted by mosquitoes.
– As beavers do not appear to increase pathogen occurrence, the case for a viable beaver population in Sweden is strengthened. This knowledge is important for management, but also for planning nature conservation initiatives where beavers can do a tremendous job entirely free of charge. They restore wetlands and provide important ecosystem services that can mitigate the effects of drought, flooding and wild fires, says Lovisa Hökby.
Defence
Lovisa Hökby will defend her doctoral thesis The role of beavers and their wetlands for zoonotic pathogens: An assessment of risky habitats and habits on 23 October at SLU in Umeå.
The thesis was carried out within the Horizon Europe projects MERLIN and BEPREP. MERLIN focuses on freshwater restoration in Sweden and across Europe. In BEPREP, researchers study how future pandemics can be prevented, using MERLIN sites as research and demonstration areas.
Tularemia
Tularemia is caused by a bacterium, and people can become infected through insect bites, contact with an infected animal, or by drinking contaminated water.
If you have tularemia it is common to experience one or more of the following symptoms:
- a high fever, sometimes accompanied by chills
- feeling unwell and tired
- headache and body aches
- swollen lymph nodes
- nausea
Tularemia is found in large parts of Sweden, but is most common in Norrland. The disease is notifiable under the Communicable Diseases Act.
Source: 1177.
Contact
Lovisa Hökby, PhD student
Department of Wildlife, Fish, and Environmental Studies
lovisa.hokby@slu.se +46736241323
Frida Wengberg, Communicatons officer
frida.wengberg@slu.se +46725669778
