Brain tumour caused odd behaviour in a beaver

On the 26th October 2016 a disorientated beaver (Castor fiber) that was walking in circles was picked up by the wildlife sanctuary Faunavisie Wildcare in the north of the Netherlands. It was originally thought that the animal had been hit by a car as it was found in the ditch by the side of a busy road. However, on closer examination at the shelter, no broken bones were seen. After eating well from willow branches during the first two days at the shelther the female beaver, weighing 23kg, stopped eating. As the animal was no longer behaving oddly she was released close to the place where she had been found in the hope that she would start eating once returned to familiar surroundings. After approaching the water the beaver returned to the basket that she had been transported in. When she was encouraged into the water she only swam a brief distance before returning once again to the basket on the bank. It was decided that the beaver should be brought back to the shelter and the following day a vet took blood for further testing. Shortly aftewards the beaver was found dead in the basket.

The beaver was at least 10 years-old: Records show that, having first been caught in the Elbe region, she had been released on the 6th Novemeber 2009 as an adult animal in the Foxholstermeer just 4km from where she was later found.

Beavers are susceptible to infection with the bacteria Francisella tularensis and as the clinical signs (disorientation and circling) could have resulted from tularemia the DWHC agreed to collect the carcase for post-mortem investigation. This was performed on the 9th of November under the supervision of pathologist Marja Kik. At the time of post-mortem, the beaver weighed 17kg. A large benign tumor of the pituitary gland was discovered and it is thought that the pressure that this exerted on the adjacent brain tissue was the reason for the clinical signs. Furthermore, the beaver had meningitis caused by an unidentified single-celled organism. Other findings included stomach ulcers, lung oedema and hemorrhage. There was no evidence of tularemia.