29 CHAPTER 1 INTRODUCTION AND LITERATURE REVIEW 1.1. INTRODUCTION Diseases of wombats and most other Australian marsupials have been little studied. Recently there has been an increased interest in diseases of free-living animals and the ecological role of diseases in populations, particularly their ability to regulate animal abundance (Scott, 1988; Thorne and Williams, 1988; Lyles and Dobson, 1993; Spalding and Forrester, 1993; Robinson, 1996; Tompkins and Wilson, 1998; Daszak et al., 2000). There is also an awareness that free-living species may act as reservoirs of disease of man and domestic animals (Robinson, 1996; Daszak et al., 2000). Therefore it is an opportune time to investigate an important disease of wombats, sarcoptic mange, which may regulate wombat abundance. This is particularly relevant to small isolated populations of wombats threatened with extinction (Wells and Pridmore, 1998). In addition, sarcoptic mange is also a disease of man and domestic animals (Doube, 1982). Sarcoptic mange is a cosmopolitan disease of mammals caused by the mite Sarcoptes scabiei. There have been numerous studies of sarcoptic mange in domestic animals and in humans where the disease is referred to as scabies. In contrast there have been few studies in free-living mammals (Arlian, 1989; Burgess, 1994). However, extrapolating knowledge of the disease in other mammals to wombats may 30 be invalid since the wombat is unique as a fossorial marsupial herbivore (Wells and Pridmore, 1998). Therefore, it is necessary to assess whether sarcoptic mange in wombats is similar to sarcoptic mange in other animals and to identify any aspects of the disease peculiar to wombats. 1.2. LITERATURE REVIEW 1.2.1. SARCOPTIC MANGE IN WOMBATS Of the Australian marsupials, sarcoptic mange has only been reported in wombats and the koala (Phascolarctos cinereus) (Vombatiformes) and the common ringtail possum (Pseudocheirus peregrinus) (Pseudocheiridae) (Wells, 1971; Southcott, 1976; Domrow, 1992; Skerratt, 1998). However, sarcoptic mange rarely occurs in free-living koalas and common ringtail possums whereas it is common in wombats (Domrow, 1992; Martin et al. 1998; Martin and Handasyde, 1999). There are three extant species of wombats. The northern hairy-nosed wombat (Lasiorhinus krefftii) is now confined to a single locality north-west of Rockhampton in Queensland (Qld) (Johnson and Gordon, 1995). The southern hairy-nosed wombat (Lasiorhinus latifrons) occurs in South Australia (SA) and south, eastern Western Australia (WA) (Wells, 1995). The common wombat (Vombatus ursinus) occurs in Victoria (Vic), New South Wales (NSW), the Australian Capital Territory (ACT), Tasmania (Tas) and Flinders Island, the south-east of SA and south-east Qld (McIlroy, 1995). All are medium-sized (up to 40 kg) fossorial marsupials. However, relatively little is known about their population biology or the effect of disease on wild populations, including the major infectious disease affecting wombats, sarcoptic 31 mange (Doube, 1982; Skerratt, 1998). Sarcoptic mange is predominantly found in one of the three species of wombat, the common wombat (Vombatus ursinus) (Gray, 1937; Wells, 1971; Doube, 1982; Presidente, 1982; Skerratt, 1998). In this species, sarcoptic mange can be debilitating. Several reports of severe sarcoptic mange in common wombats describe animals as emaciated and lacking hair, with a thick dry crust, composed of keratin, many mites and their debris, bacteria and neutrophilic debris adherent to skin (Sweatman, 1971; Presidente, 1982; Skerratt, 1998). When crust is present, the disease is called hyperkeratotic, crusted or sometimes parakeratotic sarcoptic mange. In humans it is referred to as “Norwegian” scabies since the condition was first recognised in Norway in leprosy patients by Boeck and Danielssen in the 19th century (Burgess, 1994). Here, the term parakeratotic is preferred because it describes the disturbance to the process of keratinisation caused by the tunnelling of mites in the skin (Van Neste and Lachapelle, 1981; Van Neste and Staquet, 1986). Parakeratotic sarcoptic mange in wombats is similar to that found in domestic animals and humans (Skerratt, 1998). In addition, the thick crust may be fissured by the movement of the wombat (Skerratt, 1998). The underlying skin may also crack, resulting in haemorrhage, pyoderma and sometimes cutaneous myiasis (Skerratt, 1998). Sarcoptic mange may encompass the entire body of the wombat with the head, neck, shoulders and limbs most commonly affected (Skerratt, 1998). Typically, the epidermis is thickened and there is a mild, predominantly mononuclear, inflammatory infiltrate in the dermis (Skerratt, 1998). In some wombats, hypersensitivity reactions to Sarcoptes, with few mites present in the skin, occur (Munday, 1978). Intense pruritus, a characteristic sign of hypersensitivity reactions to Sarcoptes in humans and animals 32 (Arlian, 1989; Burgess, 1994), has been reported in wombats with sarcoptic mange (Perry, 1983). Only occasional outbreaks of sarcoptic mange have been recorded in the southern hairy-nosed wombat (Lasiorhinus latifrons) (Wells, 1971) and the disease has not been reported in the northern hairy-nosed wombat (Lasiorhinus krefftii). The first report of sarcoptic mange in a common wombat was by Latreille (1818). His report contains a description of two species of mite that were collected from a mangy wombat held live at the Muséum nationale d’Histoire naturelle, Paris in the early years of the 19th century. From this description one species appears to be the mange mite, S. scabiei. The other species appears to belong to the genus Acaroptes Womersley, 1953, a genus that is commonly found on the surface of the skin of apparently healthy wombats (Womersley, 1953; Skerratt, 1998). The wombat with mange subsequently died and its preserved skin is almost certainly the one in which Duméril found mites that were considered by Fournier to be identical to S. scabiei found on man (Railliet, 1895). People who were in close contact with this wombat developed signs of scabies (Latreille, 1818; Railliet, 1895). They were treated with sulphur and the signs resolved (Railliet, 1895). Organic or metabolised products of sulphur appear to have acaricidal activity and for many years sulphur was the drug of choice when treating scabies (Burgess, 1994). The wombat from which Latreille collected the mange mites was one of three common wombats brought back alive to France on the “Naturaliste”, a ship from Nicholas Baudin’s expedition to Australia between 1800 and 1803. They were taken to the zoological park of the Muséum national d’Histoire naturelle in Paris (Geoffroy, 33 1803; De Beaufort, 1966; Horner, 1987). The skins of the common wombats collected by Baudin are still in the Muséum (De Beaufort, 1966) and one of the mounted animals has lesions consistent with mange, although no S. scabiei mites were detected in a recent examination (I. Beveridge, unpublished observations). The two mange-free wombats became type specimens of the now extinct King Island subspecies. The mangy wombat was possibly the ‘extraordinarily large wombat’ given to Baudin on board his ship the “Géographe” by the Captain of an English schooner returning from sealing whom Baudin had met two days out from Port Jackson (De Beaufort, 1966; Cornell, 1974; Horner, 1987). This wombat was transferred to the other ship commanded by Baudin, the “Naturaliste”, at Sea Elephant Bay, King Island, before the “Naturaliste” sailed for France (Horner, 1987). Womersley suggested that this wombat may have come from Tasmania (Womersley, 1953). The fact that a common wombat had sarcoptic mange in the early years of the 19th century raises the possibility that S. scabiei var. wombati is an endemic parasite of common wombats, possibly introduced to Australia by aboriginals, but it is also possible that Baudin’s afflicted wombat contracted S. scabiei from a person or one of the variety of animals (including dogs) held on the Naturaliste during its long voyage back to France (Horner, 1987). It is likely that the wombat did not have signs of mange when the Naturaliste departed from Sea Elephant Bay since all animals on board appeared healthy at the time (Cornell, 1974; Horner, 1987). S. scabiei may have been brought to Australia by the dingo (Canis familiaris dingo) several millennia ago (Corbett, 1995), since dingoes have been reported with sarcoptic mange (McCarthy, 1960a; McCarthy, 1960b; Hoyte and Mason, 1961). If S. scabiei was not present in Australia prior to the first white settlers arriving in 1788, then it is possible that there 34 have been several recent introductions of the parasite by immigrants and their animals. Dogs, foxes, pigs, horses and camels are hosts of S. scabiei in Australia (Domrow, 1992) and all have been introduced within the last 200 years (Strahan, 1995). Of these animals the one most likely to transmit S. scabiei to wombats is the European red fox (Vulpes vulpes). It occasionally utilises wombat burrows, where conditions of high humidity and low, relatively stable temperature (Brown, 1964; Triggs, 1996) appear ideal for the survival and transmission of mites (Arlian, 1989). The fox was introduced to Australia around 1850 (Rolls, 1984). If S. scabiei has been recently introduced into wombat populations then the host-parasite relationship could be a rapidly evolving one as has occurred with myxovirus in rabbits in Australia and Britain (Ross, 1982). The variety of S. scabiei found on wombats, named wombati by Railliet (1895), was formally described by Womersley (1953) (Fig. 1.1). Fain (1968) concluded that female Sarcoptes from wombats were morphologically indistinguishable from those found on many animals such as goats, sheep, llamas, horses, dogs, ferrets, rabbits and foxes. However, they could be differentiated from female Sarcoptes found on humans and some animals such as camels, cows and pigs based on the lack of a clear area within the field of dorsal scales and the inconsistent presence of ventral scales. The host specificity of S. scabiei var.wombati is unknown, although humans, dogs and koalas have developed S. scabiei infestations after contact with common wombats which were, or appeared to be, infected with S.