Under the Microscope Sarcoptes scabiei: an important exotic pathogen of wombats Sarcoptes scabiei is a parasitic astigmatid favourable for survival of the mite when mite, which causes scabies in people and Lee F Skerratt off the host. It is thought that the sarcoptic mange in mammals (Figure 1). School of Veterinary and duration of mite survival off the host is a Importantly, it is an emerging disease in Biomedical Sciences key component affecting transmission James Cook University, wildlife throughout the world 1. The mite Townsville 4811 between wombats because wombats are originates from a human ancestor and is Australia. generally antisocial and avoid contact thought to have spread to domestic and Tel: 617 4781 4838 with one another 9. Wombats rely on then free-living animals 2, 3. Based on the Fax: 617 4779 1526 burrows for diurnal shelter and recent emergence of sarcoptic mange in E-mail: [email protected] transmission may occur when wombats Australian wildlife and Aboriginal share burrows. Burrows enhance the communities, it is thought that Sarcoptes Epidemiology in wombat survival of mites when off the host by scabiei was probably introduced to populations providing a stable temperate Australia by the Europeans and their environment. animals 3,4. The mitochondrial genetic Sarcoptic mange generally occurs at low similarity of mites from Australian wildlife prevalence (0 - 15%) in common wombat Epidemics of sarcoptic mange occur and domestic animals supports this 3, 5. In populations throughout southeast sporadically within wombat populations 7,8 Australian wildlife, sarcoptic mange has Australia . Its low prevalence is and appear to be mainly associated with been reported in the common wombat attributed to high mortality and immunity introduction of S. scabiei into naïve Vombatus ursinus, southern hairy-nosed rates, resulting in the removal of populations or to occur during times of wombat Lasiorhinus latifrons, koala susceptible individuals from populations. nutritional stress such as drought, which Phascolarctos cinereus, common ringtail It rarely occurs in southern hairy-nosed are thought to lower immunity. There are possum Pseudocheirus peregrinus and wombats, which are found in South also anecdotal reports of higher 4,7 in 2003 in the agile wallaby Macropus Australia and Western Australia . The prevalences in winter, possibly associated agilis 4,6. Compared with other native difference in incidence may be attributed with increased mite survival off the host species, sarcoptic mange has by far its to differences in species susceptibility or and in populations at high density, greatest impact on wombats, particularly differences in the environment. Southern possibly associated with increased common wombats, and is capable of hairy-nosed wombats inhabit more hot burrow sharing and transmission. Foxes causing high morbidity and mortality and arid areas compared with common and dogs may be important in 7 rates . wombats. These conditions are less introducing S. scabiei into wombat populations, but are not important in Figure 1. Scanning electron micrograph of an adult female, Sarcoptes scabiei var. 7 wombati (length of body 468 mm). Note the lack of a clearing in the field maintaining its endemicity . There of dorsal scales. appears to be no sex or age predilection for sarcoptic mange in wombats 10. Clinical signs and diagnosis Clinical signs of sarcoptic mange in wombats are erythema, followed by parakeratosis and hair loss and are correlated with intensity of infection (Figure 2) 11,12. Incubation period for erythema to develop is around 14 days but occurs within 24 hours upon re- infection. The rate of development of other clinical signs is related to the dose of mites and the degree of immunity. Severe mange may take several months to develop 12. Trauma from fighting and heavy parasitism with other mites such as Acaroptes vombatus can have similar clinical signs of scale and hair loss (LF Skerratt, unpublished observations). MICROBIOLOGY AUSTRALIA • JUNE 2005 79 Under the Microscope However, thick parakeratotic scale (up to superficial layers of the epidermis where wombats 4,7. In agricultural areas, where 1cm thick) is pathognomic for sarcoptic most mites reside (LF Skerratt, wombats are considered pests, epizootics mange. Diagnosis is confirmed by the unpublished observations) 14. In of sarcoptic mange in wombats may be presence of numerous S. scabiei within addition, topical acaricides that are viewed by farmers as beneficial. However, the bottom layer of parakeratotic scale. supposed to be absorbed systemically, epizootics of sarcoptic mange together The presence of sarcoptic mange in and then redistributed to other areas of with other concomitant causes of wombat populations usually becomes the skin, will fail if they are prevented mortality, may lead to the extirpation of obvious when wombats with severe from being absorbed by parakeratotic small, isolated wombat populations mange start feeding during the day 11. scale and a thickened epidermis 14. Wildlife carers, naturalists, wildlife Injection of acaricides is the preferred biologists and rural landowners often Pathogenesis and immunity method of drug delivery. Treating with two acaricides, one systemic and the associate an outbreak of sarcoptic mange Sarcoptic mange causes emaciation and other topical, appears to be very effective with a decline in their local wombat death in wombats through a combination in reducing intensity of infection and abundance. However, most conservation of increasing the energy requirements of eliminating infection 10. Mechanical authorities do not regard sarcoptic mange the host whilst reducing the ability of the removal of parakeratotic scale and mites as a threat to the conservation of wombat to meet these additional energy by washing the wombat with a keratolytic wombats. Although sarcoptic mange is demands due to the debilitating effects of shampoo is also effective in reducing the widespread in common wombats, they the disease. Wombats with severe intensity of infection 10. This should not are abundant in Victoria, New South sarcoptic mange have restricted be attempted in debilitated free-living Wales and Tasmania and are regarded as movement, vision and hearing. The 7,15 animals since they may die from such a pests in many agricultural areas . delayed and immediate immune procedure (LF Skerratt, unpublished Common wombats are rare in 15,16 responses appear to limit mite population observations). Treatment with long- Queensland and South Australia . growth. An acquired immune response acting antibiotics is also indicated in South Australia has been the only state may increase the ability of a wombat to wombats with moderate to severe that has funded a survey of the 13 limit mite population growth . sarcoptic mange as they are predisposed distribution and prevalence of sarcoptic 7 to bacterial infections of internal organs 11. mange in wombats , possibly because Treatment common wombats are regarded as 15 There are acaricides such as the Conservation, welfare and vulnerable in South Australia . Although avermectins, which are easily applied management sarcoptic mange does not occur in the endangered northern hairy-nosed topically. However, these topical Sarcoptic mange represents a threat for wombat (Lasiorhinus krefftii), there are applications may not be totally effective if wombat populations. Whilst enzootic concerns about its possible introduction. the wombat has moderate to severe sarcoptic mange may slow or halt sarcoptic mange. This is because population growth, epidemics of In the past, control techniques for parakeratotic scale acts as a barrier to the sarcoptic mange have the ability to sarcoptic mange in wombat populations acaricide, preventing it from reaching the dramatically reduce the abundance of have been limited to the culling of severely affected animals. These animals Figure 2. Adult, male common wombat (Vombatus ursinus), from Christmas Hills, have been culled mainly for welfare Victoria with severe parakeratotic sarcoptic mange showing typical distribution of reasons because of the obvious parakeratotic scale, hair loss and excoriation. debilitating effects of severe sarcoptic mange 4. However, since severely affected animals are a major source of mites 11, culling may also reduce the transmission rate of mites and hence reduce the spread of sarcoptic mange. Recently, there have been attempts by wildlife carers to control sarcoptic mange in wombat populations with acaricides. The effectiveness of these control programs needs to be determined. Human health implications Generally, human infection with mites from wombats appears to result in self- limiting disease. Treatment with 5% permethrin can reduce duration of clinical signs of zoonotic infection by two weeks 17. 80 MICROBIOLOGY AUSTRALIA • JUNE 2005 Under the Microscope Future directions 3. Walton SF, Dougall A, Pizzutto S et al. Genetic 10. Skerratt LF. Sarcoptic mange in the common epidemiology of Sarcoptes scabiei (Acari: wombat, Vombatus ursinus (Shaw 1800). PhD Our understanding of the epidemiology Sarcoptidae) in Northern Australia. thesis 2001, University of Melbourne, International Journal for Parasitology 2004; Melbourne. of sarcoptic mange in wombat 34:839-849. 11. Skerratt LF, Middleton D and Beveridge I. populations is mostly based on anecdotal 4. Skerratt LF, Martin R and Handasyde K. Sarcoptic Distribution of life cycle stages of Sarcoptes information, one PhD study and mange in wombats. Australian Veterinary scabiei