Reliability of stained placental scar counts in farmed American mink and application to free-ranging mustelids

Asymptomatic viral infection is associated with lower host reproductive output in wild mink populations

Many endemic viruses circulate in populations without hosts showing visible signs of disease, while still having the potential to alter host survival or reproduction. Aleutian Mink Disease Virus (AMDV) circulates in many American mink (Neogale vison) populations in its native and introduced ranges. In this study, we analysed how AMDV infection in female American mink affects the reproduction of a feral population. Females infected with AMDV delivered significantly smaller litters (5.8 pups) than uninfected females (6.3 pups), meaning their litter size was reduced by 8%. Larger females and yearling females had larger litters than smaller and older females. There were no significant differences in whole litter survival between infected and uninfected females; however, offspring survival until September or October within litters of infected females was 14% lower than that within those of uninfected females. This negative link between infection and reproductive output means that Aleutian disease could seriously affect the wild mink population. This study increases our understanding of the threats posed by the spread of viruses to wildlife from farm animals or humans, highlighting that viruses circulating in wildlife, even in the absence of clinical manifestation, can be important drivers of population dynamics in wildlife.

Estimation of the Age and Reproductive Performance of Wild-Born and Escaped Mink (Neovison vison) Caught in the Wild in Denmark

Simple Summary

Previous studies of wild caught mink in Denmark showed that 30–80% had recently escaped from farms. Therefore, it is debated whether a self-sustaining feral mink population is established in Denmark or whether the population rests upon a continuous contribution of captive-born farm mink. Knowledge regarding the reproduction and mortality of mink adapted for living in the wild is important for the management of feral mink. In this study, we separated wild-born from captive-born mink caught in the wild in Denmark. To be able to age the mink in this study, an age determination model for mink was developed based on the width of the pulp cavity. The mean litter size of wild-born female mink was 7.6 (range: 5–11 kits). The annual turnover of mink caught in the wild was estimated to be 66%, and the yearly mortality was 69%; thus, the population of wild-born mink is slightly declining. The results confirmed that the wild-born mink population in Denmark is reproducing and self-sustaining without a continuous influx of captive-born mink escaped from farms. The effect of escaped mink on the wild mink population will depend on the currently unknown ability of captive mink to survive in the wild.

Abstract

The feral mink population in Denmark consists of two groups of animals: mink born in the wild and mink that have recently escaped from farms. The aims of this study were to: (1) estimate the reproductive performance and mortality of the Danish mink born in the wild (wild-born) and mink escaped from farms (captive-born); (2) discuss the likelihood of a self-sustaining population of wild-born mink in Denmark; and (3) model the relationship between the pulp cavity width and the age of mink. During 2018, 247 wild caught mink were sent for necropsy at the Danish National Veterinary Institute. Based on body length, 112 were determined as captive-born and 96 as wild-born. The mean litter size ± SE of wild-born females was 7.6 ± 0.9 (range: 5–11 kits) and for captive-born females 5.9 ± 0.9 (range: 1–10 kits). The relationship between age (in months) of mink and pulp cavity width was highly significant. Individuals with a pulp cavity width of >35% were younger than one year. Based on fecundity, the turnover of the mink population was estimated to be 66%, and the yearly mortality was estimated at 69%. Hence, the population is slightly declining. In conclusion, a feral reproducing mink population in Denmark persists without a continuous influx of captive-born mink from farms.

Effects of Mustelid gammaherpesvirus 1 (MusGHV-1) Reactivation in European Badger (Meles meles) Genital Tracts on Reproductive Fitness

Reactivation of latent Gammaherpesvirus in the genital tract can lead to reproductive failure in domestic animals. Nevertheless, this pathophysiology has not received formal study in wild mammals. High prevalence of Mustelid gammaherpesvirus 1 (MusGHV-1) DNA detected in the genital tracts of European badgers (Meles meles) implies that this common pathogen may be a sexual transmitted infection. Here we used PCR to test MusGHV-1 DNA prevalence in genital swabs collected from 144 wild badgers in Ireland (71 males, 73 females) to investigate impacts on male fertility indicators (sperm abundance and testes weight) and female fecundity (current reproductive output). MusGHV-1 reactivation had a negative effect on female reproduction, but not on male fertility; however males had a higher risk of MusGHV-1 reactivation than females, especially during the late-winter mating season, and genital MusGHV-1 reactivation differed between age classes, where 3–5 year old adults had significantly lower reactivation rates than younger or older ones. Negative results in foetal tissues from MusGHV-1 positive mothers indicated that cross-placental transmission was unlikely. This study has broader implications for how wide-spread gammaherpesvirus infections could affect reproductive performance in wild Carnivora species.

Severe parasitism by Versteria mustelae (Gmelin, 1790) in the critically endangered European mink Mustela lutreola (Linnaeus, 1761) in Spain

The riparian European mink (Mustela lutreola), currently surviving in only three unconnected sites in Europe, is now listed as a critically endangered species in the IUCN Red List of Threatened Species. Habitat loss and degradation, anthropogenic mortality, interaction with the feral American mink (Neovison vison), and infectious diseases are among the main causes of its decline. In the Spanish Foral Community of Navarra, where the highest density of M. lutreola in its western population has been detected, different studies and conservation measures are ongoing, including health studies on European mink, and invasive American mink control. We report here a case of severe parasitism with progressive physiological exhaustion in an aged free-ranging European mink female, which was accidentally captured and subsequently died in a live-trap targeting American mink. Checking of the small intestine revealed the presence of 17 entangled Versteria mustelae worms. To our knowledge, this is the first description of hyperinfestation by tapeworms in this species.

First report of Filaria martis Gmelin, 1790 in the European mink, Mustela lutreola (Linnaeus, 1761)

The riparian European mink (Mustela lutreola), currently surviving in only three unconnected sites in Europe, is now listed as a critically endangered species according to the IUCN. Habitat loss and degradation, anthropic mortality, interaction with the feral American mink (Neovison vison), and infectious diseases are among the principal causes of its decline. Surveys of helminth parasites of this host that also include focus on subcutaneous potentially pathogenic helminths such as those belonging to the genus Filaria are very scarce. We report here the presence of specimens of Filaria martis in the subcutaneous connective tissues of three M. lutreola individuals from Spain. This is the first finding of a subcutaneous nematode in a representative of the genus Mustela. The report also enlarges the known range of the definitive hosts of this nematode. These worms were mainly located in the dorsal region of mink and more rarely in the knees, elbows, and hips. Skin sloughing was only observed in one M. lutreola with both septicaemia and an associated high burden of F. martis. Therefore, more attention should be paid to potentially pathogenic helminths when designing conservation programs dedicated to M. lutreola.