Is a new ‘mystery parasite’ likely to stop the recovery of the UK otter population? It appears that we can hope not, but can’t yet be sure. I recently came across a mention in the magazine of the local wildlife trust of such a parasite spreading through otter populations in the south-west of England. The British population of otters (Lutra lutra) has been recovering in recent years, following a decline between the 1950s and the 1970s caused by pesticide pollution and habitat loss, and a new threat would be of concern.

An Internet search revealed that the parasite in question is the gall bladder fluke Pseudamphistomum truncatum, and a search of CAB Abstracts for this species found (as might be expected for a newly introduced species) just two records about its occurrence in the UK (Simpson, V. R. et al.: Veterinary Record (2005) 157 (2), pp. 49-52; Tomlinson, A. and Simpson, V.: Veterinary Record (2006) 158 (2), p. 69); the number of cases reported was small, but the Cornwall Wildlife Trust website ( indicates that the Wildlife Veterinary Investigation Centre, where the authors of these papers work, is looking into whether the considerable increase in otter deaths reported in Somerset in 2006 is related to the parasite.

Most of the other articles on P. truncatum come from its main natural range in eastern Europe (from where it is thought to have been introduced to the UK in imported ornamental fish), and report its presence in a variety of host species including otters. Few mention any effect on populations, although a Russian conference paper from 1972 mentions it as one cause of losses of seals (Phoca caspica) in the Caspian Sea, and an article from 1982 reports that these seals had a high prevalence of infection and that infected seals were undernourished and less successful at reproduction. It can be hoped that, if P. truncatum can coexist in eastern Europe with healthy populations of otters of the same species as in the UK, this will be the case elsewhere, but there is always the risk that any pathogen introduced to a new area will become a serious problem, for example if local host populations have low immunity. There is also the potential for P. truncatum infection to spread to pet animals (or even to people if they eat undercooked fish).

The subject of introduced diseases is much too big to discuss in a brief blog entry, but examples where introduced parasites have had significant effects on species of economic or conservation interest include the nematode Anguillicola crassus in European eels, Anguilla anguilla (67 records mentioning both these species in CAB Abstracts since 1998; for an overview see Kirk, R.S.: Fisheries Management and Ecology (2003) 10 (6), pp. 385-394), and avian malaria in native Hawaiian birds (for an overview see Riper, C. van: Bulletin of the Society for Vector Ecology (1991) 16 (1), pp. 59-83). Anyone interested in such diseases, and other invasive species, might like to go to to read about the Invasive Species Compendium that CABI is currently developing.

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