Stoat and weasel: DWHC focus species 2017

Two small mustelid species that are found in the Netherlands, the stoat (Mustela erminea) and the weasel (Mustela nivalis), have been chosen as the Dutch Wildlife Health Centre’s focus species for 2017. These species were chosen as relatively little is known about their distribution and disease status in the Netherlands. The aim of the DWHC focus species campaign is to encourage the submission of stoats and weasels that have been found dead for post-mortem investigation in order to shed light on the causes of death and the incidence of pathogens such as bacteria and parasites. Furthermore, material from each received animal will be stored in order to help us to address other research questions that may arise in the future. Whilst it is possible that not every reported stoat or weasel carcase can be used in this study, the reporting alone is valuable as it contributes to our knowledge about the distributions of these species. The Dutch Mammal Society is also doing research into these species in the Netherlands: for the second year in a row, in 2017 they will be looking at stoat and weasel populations in the context of the agri-environment in several locations throughout the provinces of North-Brabant and Overijssel.


The stoat and the weasel are reasonably rare in the Netherlands. Both animals are listed as ‘sensitive’ on the conservation Red List. As a result of their low numbers, small size and relatively secretive lives, carcases are rarely found. It is not known if or to what extent disease plays a role in these low numbers. Research into the causes of disease and death in these species has been relatively limited compared to that concerning their larger relation, the badger.


The most common parasites in stoats and weasels are the roundworm Skrjabingylus nasicola and the fluke Troglotrema acutum. Studies in other countries have shown that these parasites are often seen in the sinuses of mustelids. In the smaller mustelid species these parasites can cause swellings and distortion of the skulls, possibly even eroding through the frontal bones.

Of these two worms only Skrjabingylus nasicola  has been found in the Netherlands to date. Research carried out during the  1970s showed that 41% of stoats and 56% and weasels had skull lesions consistent with infestation with this worm (Van Soest et al., 1972). By focussing on these species the DWHC will investigate whether the incidence of infection with this roundworm has changed. Furthermore, it is hoped that post-mortem will reveal whether or not these skull lesions can be fatal.

Given that their diet includes prey such as mice, stoats and weasels may be affected by other diseases such as toxoplasmosis, tularemia and trichinellosis. Paratuberculosis has also been found in stoats, however, it is not clear as to how this condition affects these animals (McDonald & Lariviere, 2001). Stoats and weasels generally do not live longer than 1-2 years which means that chronic disease such as tumors are rarely found (McDonald, 2001)

Report sightings of weasels and stoats

In order to get a better idea about the distribution and common causes of death in small mustelids, the Dutch Mammal Society and the DWHC are calling on members of the public to report sightings of these animals (live and dead). Live animal sightings can be reported on of If you find a fresh carcase please keep it in a cool place (do not freeze it) and report it to the DWHC via the DWHC Submission form. We will contact you to discus whether or not the animal can be collected for further testing.

First quarter results: Of the seven animals were reported to the DWHC only one weasel could be collected as the other carcases were no longer fresh. The cause of death was trauma, most likely inflicted by a predator: there was no infection with Skrjabingylus nasicola.


McDonald, R.A. & S. Lariviere (2001). Diseases and pathogens of Mustela spp, with special reference to the biological control of introduced stoat Mustela erminea populations in New Zealand, Journal of the Royal Society of New Zealand, 31:4,721-744, DOI: 10.1080/03014223.2001.9517671

McDonald, R. A., M. J. Day, R. J. Birtles (2001). Histological evidence of disease in wild stoats (Mustela erminea) in England. The Veterinary Record, 149, 671-675

Soest, R.W.M. van, J. van der Land & P.J.H. van Bree (1972). Skrjabingylus nasicola (Nematoda) in skulls of Mustela erminea and Mustela nivalis (Mammalia) from the Netherlands. Beaufortia 20:265, 85-97.