Reintroducing beavers Castor fiber to Britain: a disease risk analysis

Abstract

Eurasian beavers Castor fiber are potential hosts for a range of infectious diseases and parasites, including those typical of common European rodents. A number of infectious organisms are potentially zoonotic and may be notifiable under animal health legislation. The official trial beaver reintroductions to Scotland, the retrospectively licensed releases in England, and the increasingly obvious presence of large numbers of unlicensed illegally released animals have highlighted potential disease risks. We aimed to conduct a disease risk analysis, based on peer reviewed publications, for selection and health screening of Eurasian beavers prior to release into the wild in Britain. Adapted from the International Union for the Conservation of Nature’s ‘Guidelines for Disease Risk Analysis’, a four‐step process was used to formulate a disease risk analysis: 1) problem description; 2) hazard identification based on literature review; 3) risk assessment, which resulted in categorisation of pathogens into low, medium, and high risk; and 4) risk management: identification of mitigating measures, followed by risk re‐evaluation in light of the reported effectiveness of the mitigation measures. The highest‐risk pathogens identified in the literature review process included: parasites, specifically Cryptosporidium parvum, Echinococcus multilocularis, Eimeria spp., Fasciola hepatica, Giardia spp., Trichinella britovi; bacteria, specifically Escherichia coli, Franciscella tularensis, Mycobacterium avium, Salmonella spp., Yersinia spp.; a fungus Chrysosporium parvum (Emmonsia parva); and terrestrial rabies virus. Most could be mitigated by sourcing beavers from Britain. The rest could be mitigated by pre‐release testing procedures that are already established. The risk of introducing significant disease to humans, domestic animals, or wildlife by releasing into the wild in Britain a beaver that was captive‐bred in Britain or a wild beaver from Scotland, based on the current evidence of disease incidence, and assuming the use of robust, peer reviewed, pre‐release health screening techniques, can be viewed as low.

Eurasian beaver (Castor fiber) health surveillance in Britain: Assessing a disjunctive reintroduced population

“…No evidence of significant zoonotic disease has been apparent with negative results for E. multilocularis, Giardia spp., Francisella tularensis, Campylobacter, Salmonella and Mycobacterium spp. supporting previous low disease risk assessments for significant zoonosis in beavers in Britain 20 . Giardia spp.…”

“…The River Otter Beaver Trial is a scientifically monitored trial reintroduction of Eurasian beavers and will conclude in March 2020. The Tayside and Devon populations have established outside of statutory procedures, through unlicensed releases and/or accidental escapees, therefore not subject to IUCN reintroduction guidelines and formal disease risk analysis 20 . Therefore, they are of unknown origin and health status with no baseline data collected on the originally released individuals.…”

“…11 The range of pathogens that can be harboured by the Eurasian beaver has been previously reviewed along with pre-release health screening recommendations for beaver importation to Scotland. 10,20 Beavers can carry host-specific parasites that were previously present in Britain, but which died out with their demise, which include the beaver beetle Platypsyllus castoris, a stomach nematode Travassosius rufus and a specialised trematode or intestinal fluke Stichorchis subtriquetrus. These species have now all been recorded in wild beavers in Scotland.…”

“…Like all other rodents, beavers may harbour common European rodent pathogens. 10,20 For any beavers of unknown origin, the presence of Echinococcus multilocularis and Francisella tularensis (the causative agent of tularaemia) would be of concern as these are notifiable diseases under EU law, significant zoonoses, not currently present in the UK and have been reported in Eurasian beavers in continental Europe. 20,23,24 Other significant diseases and parasites associated with beaver reintroduction (i.e.…”

“…10,20 For any beavers of unknown origin, the presence of Echinococcus multilocularis and Francisella tularensis (the causative agent of tularaemia) would be of concern as these are notifiable diseases under EU law, significant zoonoses, not currently present in the UK and have been reported in Eurasian beavers in continental Europe. 20,23,24 Other significant diseases and parasites associated with beaver reintroduction (i.e. those which are Notifiable under EU Animal Health legislation and/or are likely to result in significant disease to domestic animals and humans) according to DEFRA (the UK Government's Department for Environment, Food and Rural Affairs) are considered to be Cryptosporidium spp., Giardia spp., Leptospira spp., Mycobacterium bovis (bovine mycobacteriosis) and Salmonella spp., which is supported by a recent peerreviewed Eurasian beaver disease risk assessment.…”