4.12 Beavers and Population and Human Health
The following section provides narrative on how beaver activity affects population and human health.
4.12.1 Population - General overview
The Beavers in Scotland ( BiS) report ( Annex 1) summarised work that examined the interaction of beavers with the Human Environment. Beavers can provide a range of ecosystem services. These include 'provisioning ecosystem services' such as increased ground water storage, 'regulation and maintenance ecosystem services' such as flow stabilisation and flood prevention, and 'cultural ecosystem services' that relate to people's recreational, educational and spiritual interactions with the environment. They can act as agents of natural change and restoration. These all contribute to human wellbeing and have socio-economic impacts
The BiS report also considered the socio-economic implications of beaver presence at both Knapdale and Tayside, the arguments of which are largely outwith the scope of the environmental assessment. However, it did illustrate the social value that some people and local communities place on having beavers reintroduced into the environment. This was further illustrated in the public support for beaver reintroduction which came out of a number of public consultation and survey exercises done since the late 1990s. These benefits include recreational and educational value, and the 'non-use' value attributed to the reintroduction of a charismatic species.
The differences in the natural environmental characteristics between the two Beaver Policy Areas have been highlighted throughout this report. Similarly, there are considerable differences in the human environment. Maps 18 and 19 in Appendix 1, illustrate the extent of the overlap between built up areas and the core beaver woodland. The Tayside catchment has a considerably greater amount of physical development than Knapdale, but in both cases the larger concentrations of built up areas, understandably, are largely outwith core beaver woodland. However, particularly in the Tayside Beaver Policy Area, there are a number of rural and remote properties that will coincide with core beaver woodland and the potential for impacts to built-up areas, roads, rail and other infrastructure that are hydrologically linked to areas used by beavers.
There is no data available at the moment to quantify the extent of any beaver influence but the understanding of flood risk is constantly developing. The National Flood Risk Assessment ( NFRA) was published by SEPA in December 2011 and is to be re-released in 2018 to include among other factors:
- Improvements in our understanding of flood hazard;
- Consideration of communities across Scotland that have experienced flooding;
- Availability of climate change scenarios;
- Research and development that has refined understanding of impacts and influencing factors.
SEPA are also currently reviewing the methodology for designating Potential Vulnerable Areas ( PVA) and expects to apply this from April 2017 with new Draft PVAs published at the end of the year. Local Authorities in the Tayside Beaver Policy Area, in line with LA across Scotland have recently published Flood Risk Management Plans and identified several Flood Studies. These took account of SEPA's flood risk maps which are included in Appendix 1 (Maps 14 and 15 illustrate the coincidence of potential core beaver woodland and low probability flood risk in rivers). Strategic scale documents may consider the presence of beavers but impacts from the activities of beavers is likely to be at a local scale and may best be considered in Flood Studies.
Casework handled by SNH in the Tayside area highlights some of the issues and perceived issues arising from the presence of beavers in or near built-up areas where flooding is a hazard.
In Pitlochry, on the Moulin Burn, beavers had built a dam, enhanced a pre-existing pond and felled trees. This presented a flood hazard to the culverted burn and residential and commercial property on it. Following work from the Local Authority Flood Team to prevent further incursions from beavers present in the nearby River Tummel and with the advice and cooperation of the Flood Team the beavers were trapped and relocated out of the Burn.
In Bridge of Earn a family of beavers had set up a dam and lodge on a small stream running between a row of gardens and public open space. Downstream from the area is a PVA with constructed flood defences protecting several residential properties. It was feared by some local people and the Community Council that the presence of beavers increased the risk of blockage and consequent flooding. The Local Authority Flood Team were able to advise that this was a perceived rather than real risk and so beavers remain in the heart of the village with local impacts being managed by voluntary effort and riparian owners.
In July 2015 a significant flood event occurred in Alyth. This caused significant local damage to property and infrastructure both within and downstream of the town. Four footbridges collapsed, and a number of mixed commercial and residential properties were affected along with two electrical substations. This last resulted in around 700 properties being left without power. At least 59 properties and businesses were thought to be flooded internally. The presence of several families of beavers with associated lodges and dams upstream of the town was thought by some to have contributed to the flooding by the addition of debris which choked bridges and culverts. The flood event was described and investigated by the local authority, SEPA and SNH and reported in the Joint Agency Report on the Flooding in Alyth of 17 July 2015 PKC, SEPA, SNH September 2015. The report concluded that the presence of beavers upstream had little if any impact on the flooding either positively in attenuating the peak or negatively by adding to the debris. All the beaver dams present before the flood were present after the event.
There is also increasing interest in the role beavers may play in 'Natural Flood Management' ( NFM) especially in situations where they may modify their local environments in higher, upstream catchment areas. Although there is information on the roles beavers can play in hydrological and geomorphological processes (e.g. section 4.10), it is less clear how this may contribute to NFM. SNH will therefore investigate opportunities for investigating this further.
Settlements with a history of flooding are well documented in the Tayside Policy Area. The presence of beavers may be perceived as increasing the risk to households. Whilst strategic scale documents could take account of the presence of beavers, impacts from the activities of beavers are likely to be at a local scale and may best be considered in Flood Studies or on a case by case basis.
There are a number of methods that can be used to protect infrastructure and settlements and in some cases it may be prudent to protect especially sensitive interests before problems arise. This is more achievable for small-scale structures, such as culverts under roads or in bridge design. Scotland could draw on European approaches to protection of settlements and GIS-based tools to identify areas where beaver activity is predicted to be more likely.
This will need to include guidance on management techniques (for both pre-emptive and reactive actions) and information on sources of advice and support. The effectiveness of beaver management in Scotland will increase over time as experience is gained and methods refined.
Section 5 also details the hierarchy of mitigation techniques that can be used to address impacts from beaver activities, including generic management and licencing approaches to more practical measures including those to address:
- Dam building activities
- Burrowing activities and
- Foraging activities
These mitigation measures apply to the potential negative effects identified in relation to beaver activity and infrastructure.
4.12.2 Human Health
The section below considers the health implications of the Policy. To ensure this issue is comprehensively reported, the following sections detail potential health interactions between beavers and humans. However, animals used for the Scottish Beaver Trial ( SBT) were quarantined and screened before and monitored after, release, and there was a programme of public health monitoring at Knapdale. A sample of Tayside beavers were also tested for a range of parasites and diseases and no evidence was found of pathogens that may cause an increased health risk to humans, livestock and other wildlife.
The conservation translocation of a species involves a whole 'biological package', reflecting the assortment of bacteria, viruses, fungi, parasites and other micro- organisms which any single animal or plant, such as a beaver, may naturally harbour. Some of these additional organisms have the potential to become pathogenic (i.e. capable of causing disease), while others may be present (although not necessarily prevalent) and exert no discernible effect upon its host or the wider receiving environment.
These additional organisms have the potential to influence the fitness and survival of individual beavers. Translocated animals may be vulnerable to stress-induced immunosuppression, or a lack of acquired immunity from previous exposure. Existing wildlife may act as a reservoir for infection and could ultimately affect the success of any reintroduction project. Populations of wild and domesticated animals and humans alike could be at risk through the transfer of new zoonotic diseases or the addition of new transmission pathways for existing pathogens.
Clinical veterinary examination and screening is therefore a fundamental part of understanding how disease transfer mechanisms influence beaver health and survival as well as the risk to wider indigenous, domestic and human populations. Reintroduction is increasingly being used as a conservation tool with at least 203 known beaver translocation projects (outside the former Soviet Union) since the first known reintroduction in Sweden in 1922. Despite long-standing recommendations and a general acceptance that pre-release health screening is good practice, little baseline health status information has been published for many translocated species, including beaver.
Eurasian beavers host a number of external and internal parasites. A list of common European rodent diseases and parasites associated with beavers has recently been compiled. Some of these are already present in the UK (e.g. Cryptosporidium parvum) and some are not (e.g. Echinococcus multilocularis). Many of these rodent diseases and parasites have the potential to cause zoonotic diseases and may be notifiable and/or reportable in the UK.
Beavers may be involved in the transfer and hosting of diseases and parasites in three main ways:
1. Beavers acting as a mechanism for the introduction of new or eradicated diseases and parasites, and acting as potential transmission routes for the infection of humans, domesticated livestock and existing wildlife.
2. Diseases and parasite transfer from existing wildlife populations to translocated and wild beavers (see Annex 1 section 4.6).
3. Beavers acting as a reservoir host for infectious diseases and parasites already present in Scotland, with potential transmission routes for infection of humans, domesticated livestock and existing wildlife.
Prior to the Scottish Beaver Trial ( SBT), little information was published on beaver health surveillance, disease or mortality despite the relatively large number of beaver translocation projects across Europe and elsewhere. A beaver health surveillance programme for the SBT was established that addressed International Union of Conservation of Nature ( IUCN) and governmental guidelines, as well as public health concerns. This included pre-release health screening and regular post-release monitoring including the post mortem examination of all cadavers. It was used as a template for a health screening programme carried out on a sample of live and dead beavers from Tayside. During the SBT there was also public health monitoring by independent local authority specialists. At a wider scale, and once the SBT was completed, the Centre of Expertise on Animal Disease Outbreaks ( EPIC) also undertook a public health risk assessment of Cryptosporidium and Giardia posed by beavers in Scotland .
The commentary provided below explores the influence of beavers on the potential for disease transfer to humans and makes reference to interaction with existing wildlife and domesticated animals where relevant. Each parasite / disease is discussed in turn with an overview of the life cycle and how this involves beavers and human populations. The implications from which are then discussed with respect to the two beaver areas and policy.
22.214.171.124 Introduction of new or eradicated diseases
Beavers acting as a mechanism for the introduction of new or eradicated diseases and parasites, and acting as potential transmission routes for the infection of humans, domesticated livestock and existing wildlife
Alveolar Hydatid Tapeworm Echinococcus Multilocularis
E. multilocularis is one of the most pathogenic parasitic zoonoses in the northern hemisphere and is the causative agent of alveolar echinococcosis disease in humans It is endemic in large parts of Europe and has recently been identified in Sweden. Adult tapeworms live in the small intestine of the definitive (final) host, usually red foxes. Eggs are shed into the environment with host faeces. Small mammals, which are the main intermediate host, are then infected through ingesting parasite eggs. The indirect wildlife-based life cycle is then completed by carnivorous predation of an infected intermediate (non- egg-shedding) host.
Infection of unusual intermediate hosts, such as beavers, occurs through an increase in infected foxes leading to heavy environmental contamination with eggs. The first cases of beaver infection were reported in Switzerland and Austria, and more recently in Serbia
Finland, Ireland, Malta and the UK are considered free of E. multilocularis, and in order to maintain this status these countries are obliged to implement surveillance programme aimed at detecting the parasite in any part of the country (Regulation ( EU) No 1152/201130). As with previous surveys, the recently published report on the 2012-2013 surveillance of UK fox populations did not identify any E. multilocularis. The translocation of beavers from central Europe is generally accepted to present a risk of importing the disease.
Implications of beaver policy
Beavers imported for the SBT were not considered to present a risk, as the donor country, Norway, was considered free of E. multilocularis. At the time of trapping, there was no diagnostic test available for live animals.
The animals on Tayside were from unknown sources. Recently developed techniques, including in-field laparoscopy and abdominal ultrasound, were used to diagnose E. multilocularis abdominal lesions together with corroborative immunoblotting. None of the beavers tested from the Tayside catchment using these techniques were positive for E. multilocularis.
Previous assessments have concluded that the risk of this tapeworm becoming established as a result of infected beavers imported from E. multilocularis-free areas is negligible, and is low but very uncertain for those from endemic areas.
It follows, therefore, that the risk appears negligible for the beavers at Knapdale, as well as for other wildlife and humans. The risk associated with any future releases of beavers at Knapdale would need to be re- assessed, taking into account the origin of the animals. The situation at Tayside is more complicated in that the origin and health status of the entire beaver population is unknown, although no evidence of E. multilocularis has been found in the sample tested.
Health assessment and pathogen screening before release of any animal is regarded as a key requirement in any translocation. There is now an effective diagnostic test for live animals, together with serological screening. Such testing would provide further reassurance that the parasite does not become present in the wild in Scotland as a result of any beaver translocation and therefore not pose any threat of human infection.
Rabies is an acute infection of the central nervous system caused by a lyssavirus of the Rhabdoviridae family. It affects all mammals, including humans, and the main reservoir is wild and domestic canids (e.g. dogs, wolves and foxes). The notification of rabies in humans and animals is mandatory in most member states across Europe.
The last case of classical (sylvatic) rabies in an animal outside of quarantine in the UK (a dog in Newmarket) was in 1970, although the related European Bat Lyssavirus, which causes the same clinical symptoms as classical rabies, has been recorded in a small number of wild British Daubenton's bats since 2002. The last case of human terrestrial rabies acquired in the UK was in 1902; however occasional travel-related cases do occur. Between 2000 and 2012, there were five cases of imported human rabies in the UK. There were no human cases of rabies infection in the UK in 2013.
The import of beavers to the UK is subject to strict animal health and disease-control legislation, notably The Rabies Importation (Dogs, Cats and other Mammals) Order 1974 (as amended) as well as The Balai Directive. The quarantine period, where required, is deemed sufficient to prevent the entry of rabies.
Implications of beaver policy
A total of 27 European beavers were imported from Norway for use in the SBT. They were quarantined for a period of six months during which time six individuals died with no common cause identified. In view of these mortalities, and the fact that Norway is considered free of classical (sylvatic) rabies, the RZSS received permission to import a further four Norwegian beavers without the full quarantine requirements. This was subject to strict criteria, including the need for four weeks' quarantine in Norway under veterinary supervision.
There is no reason to believe that any further import of beavers for Knapdale, would increase the risk of rabies, provided appropriate statutory animal health procedures are followed.
Tuaraemia ( Francisella Tularensis)
F. tularensis is an intracellular bacterium found in a wide range of invertebrates, birds and mammals, with transmission to humans causing tularaemia via contamination of food or water, or through bites from infected insects. It has a broad geographical distribution across Europe but does not occur in the UK. Human outbreaks appear to follow outbreaks in rodents, examples include common voles and water rat in the Russian Federation as well as vole and hare populations in Sweden.
It is thought to be spread in the environment by rodents, particularly water voles but also squirrels (Sciuridae), muskrats Ondatra zibethicus, beavers and rabbits (Leporidae). However, there is no evidence to suggest that any of these species constitute a natural reservoir of this bacterium.
Implications of beaver policy
None of the 29 beavers tested at Knapdale were antibody positive for F. tularensis, nor were any of those tested at Tayside.
Health screening during quarantine provides an opportunity to test for infection with F. tularensis and, if necessary, to act accordingly to ensure that the UK remains free of the pathogen. If captive animals already present in the UK were used to bolster the population at Knapdale, then they would require screening for F. tularensis (and other pathogens/parasites) as they may not have been subject to any additional health testing during the original rabies quarantine.
126.96.36.199 Beaver acting as a reservoir host
Beavers acting as a reservoir host for infectious diseases and parasites already present in Scotland, with potential transmission routes for the infection of humans, domesticated livestock and existing wildlife.
Leptospira bacteria have been found in virtually all mammalian species and the associated pathogenic disease, leptospirosis, is the most widespread zoonosis worldwide present in all continents except Antarctica. Humans most commonly acquire infection through occupational, recreational or domestic contact with the urine of carrier animals either directly or via contaminated water or soil.
There is a general paucity of information exploring the relationship between beavers and Leptospira spp, although it has been documented in North American beavers from a number of Swiss zoos. Elucidation of the role of free-living beaver as a potential reservoir host for Leptospirosis was attempted in South-West Germany through examination of kidney tissue of 26 beavers found dead. Whilst positive results were detected in four of the beavers, cause of death was not attributed to pathogen infection. Infection in humans is usually associated with recreational activities (e.g. triathlon) with the transmission pathway via contaminated water and small skin lesions or other injuries.
Implications of beaver policy
Pre-release testing at Knapdale found five animals positive for Leptospira antibodies. Post-release testing found two animals seropositive for Leptospira. None of the 17 beavers tested positive at Tayside.
Given the widespread nature of Leptospira infection (160 mammalian species have been identified as a natural carrier) and the lack of evidence of beaver as a reservoir host, it would seem likely that the additional risk to existing wildlife populations at Knapdale and Tayside, and therefore onwards to humans, would be minimal.
Continued health surveillance of both beaver populations would help to verify this assessment in the longer term. Any significant increase in beaver numbers across Scotland in the longer term could conceivably lead to a greater overlap of human recreational activity in areas inhabited by beavers. However, the risk of acquiring leptospirosis appears to be highest among farmers, veterinarians and sewer workers, who all work around animals, rather than among those engaged in recreational activity.
Cryptosporidium species are intestinal, protozoan parasites of mammals that cause cryptosporidiosis, the symptoms of which may include life-threatening diarrhoea in immunosuppressed humans and young livestock. Disease in humans is predominantly caused by C. parvum and C. hominis. Rodents are considered important reservoirs of the parasite. It is considered endemic in most cattle holdings and is common in sheep and deer. Cryptosporidiosis is relatively common in animals in Great Britain. Infection in humans most commonly occurs through the consumption of food or water, but can also occur through the exposure to faeces in the environment, contact with infected animals and person-to-person contact.
Cryptosporidium are shed from the gut in faeces as environmentally-resistant oocysts which are able to survive in water or moist soil for several months. Faecal screening of 182 beavers in Norway found no oocysts in any sample despite the frequent occurrence of oocysts in surface water sources.
Implications of beaver policy
No Cryptosporidium was detected from beavers screened during quarantine and prior to release at Knapdale. Cryptosporidium was detected in a dead wild-born beaver kit at Knapdale, suggesting that the parasite was acquired from existing sources in the wider environment. One beaver from Tayside was found to be positive for Cryptosporidium following faecal examination. The individual was in good body condition with no signs of ill health.
Public health monitoring at Knapdale showed that Cryptosporidium is present in the existing wild mammal population. Many of the surface waters across Scotland are contaminated with Cryptosporidium. The additional risk to human health from the presence of beavers in Knapdale has been assessed as very low.
At a wider scale, the Centre of Expertise on Animal Disease Outbreaks ( EPIC) consider the likelihood of beavers acting as an important source of contamination of Cryptosporidium to water supplies as 'very low to low (high uncertainty)' in the context of other sources of contamination, such as humans, livestock, other wildlife and domestic animals.
As a precaution, and to provide further reassurance, it has also been recommended that there is enhanced surveillance of human cases for a set period; further reintroduction proposals should be discussed with local authority environmental health teams and Scottish Water to allow levels of risk to be evaluated; and best practice in relation to public and private water supplies should continue to be promoted.
Giardia duodenalis (also known as G. lamblia or G. intestinalis) is an intestinal, protozoan parasite of mammals. It causes giardiasis, the most common cause of parasitic, diarrhoeal disease in humans worldwide. It was the most frequently raised public health issue relating to beavers prior to the SBT, perhaps because giardiasis is sometimes referred to as 'beaver fever' in North America.
Studies of Giardia prevalence showed rates of 8% in Eurasian beavers in Poland, and 7-16% in North American beavers in the USA. In comparison, other semi-aquatic rodents, such as muskrats, are thought to constitute a more important reservoir with a much higher prevalence of 37-96%.
Faecal screening of 241 beavers in Norway found no Giardia cysts, despite the frequent presence of the parasite in Norwegian surface water sources. A 2002 study noted that there had been no waterborne outbreaks of giardiasis reported in Norway despite having a beaver population of over 50,000 animals at the time, and the rate of giardiasis in the human population was similar to that of Scotland that had no beavers (with most cases originating from travel abroad).
A single study in Colorado found that beavers shed Giardia cysts in their faeces throughout the year, with temporal variation in prevalence. They became infected as kits and remained so into adulthood, presumably related to their coprophagic (eating of faeces) behaviour. This led to the suggestion that beavers act as an 'amplification host'.
Implications of beaver policy
Giardia was not detected during the screening of the Knapdale beavers, before or after release. This suggested that no transfer had occurred from wildlife populations to beavers during the trial, and therefore it was also unlikely that any of the beavers acted as a reservoir for other wildlife populations. There were similar observations at Tayside, with no detection of Giardia in beavers.
Public health surveillance monitoring carried our as part the SBT assessed the additional risk to human health from the presence of beavers in Knapdale as very low. While the presence of Giardia cysts in the watercourses at Knapdale means there is potential for individual beavers to become infected, it should be noted that there has been no evidence to date of such transmission occurring in Norway.
Continued health screening of beavers to confirm the presence of this parasite in the beaver populations at Knapdale and Tayside would also help elucidate any amplification role given the lack of evidence for this in the published literature.
At a wider scale, EPIC considers the likelihood of beavers acting as an important source of contamination of Giardia to water supplies as 'very low to low (high uncertainty)' in the context of other sources of contamination, such as humans, livestock, other wildlife and domestic animals. However, as a precaution, and to provide further reassurance, it has also been recommended that there is enhanced surveillance of human cases for a set period; further reintroduction proposals should be discussed with local authority environmental health teams and Scottish Water to allow levels of risk to be evaluated; and best practice in relation to public and private water supplies should continue to be promoted.