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  • Journal of The Royal Society of New ZealandVolume 31 Number 4 December 200] pp721 744

    Diseases and pathogens of Mustela spp., with specialreference to the biological control of introduced stoatMustela erminea populations in New Zealand

    Robbie A. McDonald*, Serge Larivieref

    Controlling populations of introduced stoats is a high priority for the conservation ofavian biodiversity in New Zealand Existing technology for stoat control is labourintensive and expensive, therefore new techniques and approaches, such as biologicalcontrol, are needed We reviewed the literature on the diseases and pathogens of stoats,and closely related mustelids, with a view to identifying potential biological controlagents Aleutian disease virus, mink enteritis virus, and canine distemper virus holdpromise as agents of lethal control, though the risks to non-target species posed by theseviruses are serious Host-specific ectoparasites such as Tnchodectes ermineae, nematodessuch as Skrjabingylus nasicola, and bacteria such as Hehcobacter mustelae andBartemella spp could have a role as vectors for the transmission of fertility controlagents We urge some caution in developing biological control technology without aparallel investigation of the potential effects of biological control on stoat populationsand the resulting survival of threatened birds

    Keywords biocontrol conservation ferret mink Mustelidae pest management predator control wildlife disease


    The endemic fauna of New Zealand has evolved in the absence of mammalian predators andhas proven particularly vulnerable to some of the mammals introduced since human settlement(King 1984) Stoats Mustela erminea, weasels M nivahs, and ferrets M furo were introducedto New Zealand in the 1880s in an attempt to control rabbits Oryctolagus cuniculus (King1984) Stoats were almost immediately implicated in the declining abundance of native birds,a trend initiated by the earlier arrival of numerous other mammalian predators In the 21stcentury, stoats are still contributing to the decline of native fauna They now present a seriousthreat to the future existence of several endemic bird species (McLennan et al 1996,O'Donnell et al 1996, Wilson et al 1998) McDonald & Murphy (2000) provided a recentreview of the problems caused by stoats and of the steps taken so far to manage stoats in NewZealand

    'School of Biological Sciences, University of Bristol, Bristol BS8 1UG, UKPresent address Game Conservancy Trust, The Gillet, Forest in Teesdale, Barnard Castle,DL12OHA, UK email robbie [email protected] comDepartment of Biology, University of Saskatchewan, 112 Science Place Saskatoon, SK S7N iE2

    CanadaPresent address Delta Waterfowl Foundation R R #1, Box 1, Portage La Prairie, Manitoba R1N 3A1,Canada email [email protected] org

  • 722 Journal of The Royal Society of New Zealand, Volume 31, 2001

    Reducing predation by stoats is clearly essential for the survival of several endemicspecies on the mainland of New Zealand. The main effort so far has been in developing andemploying methods of lethal stoat control. Hence, current programmes rely to a greatextent on "traditional" kill-trapping using steel spring traps, which is very labour intensive.More recently, the use of stations baited with poisoned hen eggs has become widespread.These methods have proven useful in temporarily reducing stoat abundance and enhancingthe nesting success of certain birds. However, more cost-effective and sustainable approachesto controlling stoats are urgently needed.

    The use of diseases as agents of biological control is often the most appealing of a rangeof options for the control of pest species (van Driesche & Bellows 1996; Lynch 1998;Courchamp & Sugihara 1999; Norbury 2000). The objective of our review was to provideecologists with an accessible account of the literature on stoat diseases, with particularreference to areas that may be pertinent to the biological control of stoats in New Zealand.A range of infectious diseases can affect small mustelids but they have not received asmuch attention as the diseases affecting larger carnivores (Murray et al. 1999). Consequently,the pathology and epidemiology of the numerous diseases that affect stoats are poorlyknown. Since certain aspects of the biology of stoats have not yet been described in detail,we expanded our review to take into account work on closely related species. Fortunately,the economic incentive for rearing ferrets, and mink Mustela vison, as well as conservationinterest in black-footed ferrets M. nigripes, has stimulated a good deal of research on thediseases that afflict them. Ferrets and mink are useful models for stoat disease because ofgood evidence that congeneric species are similarly vulnerable to many diseases. Forinstance, domestic ferrets, Siberian polecats M. eversmanni, and ferret-Siberian polecathybrids were extensively used as disease models in developing black-footed ferretconservation plans (Williams et al. 1991; Williams & Thorne 1996). However, it is notalways correct to assume comparable responses to infection between congeners (Williams& Thorne 1996). Where work on the biology of Mustela spp. was scarce, we have alsodrawn on literature about other mustelids.

    Diseases of the Mustelidae in captivity have been reviewed previously (Williams &Thorne 1996). While they were shown to be particularly susceptible to a range of viraldiseases, their review did not consider bacterial, protozoan, or metazoan agents of diseasein detail. The reviews provided by Davis et al. (1981) and Addison et al. (1987) areinvaluable to a consideration of infectious diseases in wild mammals and furbearers. Thegeneral reviews of stoat biology provided by King & Moody (1982), King (1983, 1989),Fagerstone (1987), and McDonald & King (in press) have also proven useful. Norbury(2000) recently reviewed the potential options for biological control of stoats, though hefocused on fertility control rather than on diseases. Here, we have reviewed studies of allknown pathogens, including viruses, bacteria, and parasites, and have presented our findingsby types of disease agent. We have outlined the relevance of disease agents to the controland limitation of mustelid populations and have identified areas that we believe will bemost productive for future research. It is likely that animal welfare will be a major topic ofconsultation during the development of biological control agents for stoats. Unfortunately,the current level of understanding of the pathology of disease in stoats is such that adetailed consideration of animal welfare would not be supportable in this review. Therefore,there remains a clear need for further investigation of welfare aspects associated with usingany novel biological control agent.

  • McDonald & LanviereDiseases of stoats 723


    Morbilliviruses and parvoviruses

    Morbi Hi viruses cause a range of wildlife and human diseases including measles, rinderpest,and canine distemper (Barrett 1999) Parvoviruses are apparently able to spread worldwide,because most viruses are not genetically distinct even when geographically separated(Parnsh 1995) Recent epidemics of morbilliviruses and parvoviruses in wildlife anddomestic animals suggest that these are highly variable pathogens capable of rapid adaptationto alternative hosts For instance, the incidence of feline panleukopema virus (FPV) incaptive large cats was suggestive of interspecific transmission from domestic dogs (Steinelet al 2000) Mustehds can also be host to non-specific parvoviruses For example, FPV,but not canine parvovirus (CPV), has been found in wild honey badgers Melhvora capensis(Steinel et al 2000)

    Isolates of phocine distemper virus (PDV) from harbour seals Phoca vituhna collectedin Denmark, Norway, Greenland, and the United States were comparatively distinct fromreference strains of canine distemper virus (CDV) However, similarities between Danishand Norwegian isolates of PDV and morbillivirus isolates from Danish mink farms suggestthat epizootics among farmed mink may have arisen by transmission from diseased seals toterrestrial carnivores (Blixenkrone-Moller et al 1992)

    Two parvoviruses that cause very different diseases have been described in mink indetail Aleutian disease virus (ADV), also referred to as Aleutian mink disease parvovirus(AMDV), is associated with persistent, low-level viral replication and chronic severeimmune dysregulation (Storgaard et al 1997) In contrast, infection with mink enteritisvirus (MEV) is associated with rapid, high-level viral replication and acute disease

    Aleutian disease virus

    Aleutian disease of mink is a naturally occurring persistent viral disease first described in1958 (Helmboldt & Jungherr 1958) It is caused by ADV and in adult mink results in achronic disease that can be broadly characterised as an immune disorder with a persistentinfection of lymphoid organs ADV is particularly lethal to the Aleutian strain of mink, butall strains are susceptible to some degree (Bloom et al 1994) The virus is transmissible toother mustehds, particularly Mustela spp including ferrets and stoats (Kenyon et al 1978,Alexandersen et al 1985) Symptoms similar to Aleutian disease have been described in anotter Lutra lutra, though while the pathology was consistent with infection by ADV, noabsolute diagnosis was provided (Wells et al 1989)

    When stoats were inoculated with ADV isolated from farmed mink, antibodies to thevirus were detected by counter immuno electrophoresis However, the stoats did not showclinical signs of the disease, I e , abnormal accumulation of lymphocytes in kidney or livercells or hyperplasia of lymphoid organs (Kenyon et al 1978) In a sample of 446 domesticferrets in England, 8 5% were seropositive for ADV (Welchman et al 1993) implying thatthere could b

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