The flatworm - called Pseudamphistomum truncatum - is thought to have been introduced by ornamental fish imported from Russia and Eastern Europe. Some escaped from ponds and are now thriving in the Somerset Levels. The worm is passed on when animals, like cats, dogs, otters and foxes eat raw fish which have been infected. The disease can - in rare cases - affect people. The worms live in the gall bladder and can cause liver damage and jaundice. 

The disease has so far been found affecting otters on the Somerset Levels, but experts fear it could spread to other animals and across Britain. 

Vic Simpson, a leading veterinary wildlife pathologist at The Wildlife Veterinary Investigation Centre, who discovered the parasite said today:

"Otters were badly affected by environmental pollution during the 1960s and 70s but they have been recovering well in recent years. This new disease is a worrying development. It is", he said, "another example of the ease with which new diseases can be introduced and which can pose a threat, not only to wildlife, but also to pets and humans alike. We urgently need to do further research on other species, such as mink, but at present do not have sufficient funds available".

Kate Stokes, Water for Wildlife Manager of the Cornwall Wildlife Trust, added "The discovery of this parasite emphasises the importance of monitoring wildlife for evidence of disease. Anyone finding a dead otter or other endangered species should report it to their local Wildlife Trust or the Environment Agency".