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Health

Rabies

The rabies virus is a mammalian disease that attacks the nervous system. The virus is present primarily in the saliva, brain tissue and spinal fluid of a rabid animal. Humans can be infected through bites from infected animals. In Western Europe rabies is mainly carried by foxes but other wild mammals, including beavers, have been known to carry the virus. Strict quarantine regulations prevent the introduction of infected animals into Britain.

Giardia lamblia

This unicellular protozoan gut parasite is already present in Britain and can be carried by almost all mammals. It is not especially associated with beavers. It can be removed from water by normal filtration methods. Norway has around 75,000 beavers and despite much of the rural population having water supplied from untreated streams the only Giardia lamblia outbreak in recent years was near Bergen, where beavers are absent. There are no reported instances of European beavers causing health problems in humans from Giardia lamblia.

Leptospirosis

This disease is caused by the Leptospira bacterium. Beaver, along with water voles and other rodents can carry this disease. Leptospira is already present in British waterways and the presence of beavers within an ecosystem is thought most unlikely to pose a significant increase in the risk to humans or livestock of contracting this disease.

Cryptosporidium

This protozoan parasite can cause gastro-intestinal illness with diarrhoea in humans. It is already present in Britain with livestock often acting as a vector. Beavers should not have any significant effect on the occurrence of this parasite in humans or livestock. There are no reported instances of European beavers causing health problems in humans from Cryptosporidium.

Tularaemia

This is caused by the bacterium Francisella tularaemis . Vectors include rodents. Transmitted by infected air and water, this bacterium occurs in Europe but is not presently found in the UK. Imported beavers would require health screening before release into any reintroduction site.

Pseudotuberculosis

The Yersinia pseudotuberculosis bacterium, causing pseudo-TB, already occurs in the UK and is not considered a significant issue for people or livestock. Most human infections are food-borne. Beavers are not especially associated with this disease.

Bovine Tuberculosis

There is no evidence that beavers carry bovine tuberculosis (bTB). As most mammals can be infected by bTB it is theoretically possible for beavers to become infected. However, the natural behaviour of beavers is such that it is highly unlikely that beavers could act as an effective reservoir for the transmission of bTB to livestock species.

Gyrodactylus salaries

This is a small (0.4mm) freshwater obligate ectoparasite of salmonids found in parts of Europe. It can only live for a short time away from a fish host and cannot swim.   It is normally spread by direct contact between fish and is not carried by beavers. There are no known cases of any non-fish species acting as vectors, apart from humans.

Echinococcus multilocularis

This is a tapeworm that causes disease (echinococcosis/hydatidosis) in certain terrestrial mammals including humans.  The lifecycle of E. multilocularis involves a definitive host and an intermediate host, each harbouring different life stages of the parasite. Canids are the definitive hosts for the adult stage of the parasite whilst rodents are the main intermediate host.  Various mammals, including beavers and humans, can be infected as intermediate hosts by ingesting eggs.  E. multilocularis is very difficult to treat in its intermediate stage and in both beavers and humans long term infection can be fatal.  E. multilocularis occurs in wide areas of the Northern Hemisphere but is currently not present in Britain.  There are currently no tests that will allow the reliable screening of beavers for infection with E. multilocularis (although work to develop a blood test is underway) and thus sourcing from populations that are free of this parasite will currently be essential in ensuring that the importation and release of beavers into Wales is not associated with its introduction.