DISEASES
The clinical signs and diagnosis of selected diseases of wombats are summarised in Table 37.1.
8.1 Sarcoptic mange
Sarcoptic mange, caused by Sarcoptes scabiei, is considered an emerging infectious disease of wildlife (Tompkins et al.
2015) and the origins, cross-species infectivity and endemicity of this pathogen have been questioned (Andriantsoanirina et al. 2015; Fraser et al. 2016; Old et al. 2017). Phylogenetic studies support the hypothesis that the pathogen was first introduced to Australian wildlife at the time of European colonisation via transmission from non-marsupial hosts (Fraser et al. 2017). Sarcoptic mange is the most frequently observed condition in bare-nosed and southern hairy-nosed wombats and is present throughout their respective ranges. It is chronically debilitating and is considered to be the most significant disease threat to free-ranging wombats. Left untreated, mange can inflict immense suffering, frequently leading to death (Skerratt et al. 2021). There have been no reports of this disease in northern hairy-nosed wombats. The specific dermatological aspects of sarcoptic mange in wombats are discussed in Chapter 12.In high-density populations the disease can spread rapidly, resulting in epizootics and local extirpations. It is environmentally transmitted with the microclimate within wombat burrows favouring off-host S. scabiei survival. Mite persistence within burrows matches or exceeds the known frequency of wombat burrow switching (Browne et al. 2021). Spatiotemporally, the disease may spread as a travelling wave through a population (Martin et al. 2017).
Biologically, wombats are notable for their restricted energetic ecology. They feed on a low-energy diet, have a low metabolic rate for their size and have relatively small home ranges. They occupy poor-quality habitat and spend less time feeding than many other herbivores.
Parasite-driven changes to energy expenditure in a species with such a conservative energy budget results in profound clinical effects (Simpson et al. 2016).Thermal imaging indicates that wombats with mange- associated alopecia have reduced insulation and altered thermal tolerance, with a resultant greater differential between ambient and body temperatures (Plates 37.1 and 37.2). Sarcoptes scabiei causes inflammation of the skin, enhancing cutaneous perfusion, which may also accelerate heat loss. Wombats with mange are likely to have greater energetic costs associated with thermoregulation and this may be linked with changes in observed behaviour. Mange alters the time allocation of above-ground behaviours: feeding rate is slower, less time is spent walking and more time is spent drinking and scratching. They are active outside the burrow for longer periods during warmer weather than their healthy counterparts. They do not, however, spend more time feeding (Simpson et al. 2016). Wombats with severe mange have poorer body condition. All these factors combined are likely to affect immunocompetence.
Ruykys et al. (2013) reported blood parameters in mange-affected southern hairy-nosed wombats that were similar to previous findings in mange-affected barenosed wombats (Skerratt et al. 1999; Hartley and English 2005). Mange was associated with significantly higher WBC and neutrophil counts and higher total protein but lower RBC counts, Hb, HCT and creatinine.
Prior to attempting treatment, mange severity, body condition, behaviour and the capacity to treat should be assessed to determine prognosis. In mild cases less than 10% of the body surface is affected; in severe cases it will be greater than 50% and lesions will be advanced. Euthanasia is justified on welfare grounds if any of the following apply: the animal is emaciated; there are severely infected wounds and/or myiasis; there is marked facial crusting leading to apparent blindness or difficulty breathing or eating; the mange score is severe (Skerratt et al.
2021).Acaricidal treament options include 0.2-0.4 mg/kg SC ivermectin or moxidectin weekly for 2-4 mo, 4 mg/kg topical moxidetin to a maximum of 100 mg/wombat weekly for 15 wk or a single dose of 25 mg/kg topical flu- raner. Topical treatment in free-ranging wombats is delivered via burrow flaps or pole scoops but the longterm and population level efficacy of such methods is questionable (Takano et al. 2023), at least partly due to pathophysiological barriers of drug retention and absorption when topcial formulations are applied to a wombat's diseased dorsum (Bains et al. 2022).
Dosage regimes that are sub-therapeutic, indiscriminate or that exceed recommendations further raise animal welfare, ecotoxicity and drug resistance concerns (Mounsey et al. 2022). Supportive care in addition to aca- ricidal therapy is positively associated with the success of mange treatment (see Table 37.1) but is only feasible for animals in or brought into a managed care setting.
Other dermatopathies (e.g. follicular atrophy, hypersensitivity reactions, bacterial, fungal and other ectoparasitic dermatoses) can mimic mild to moderate mange and diagnostic investigation including skin scrapes, histopathology and bacterial/fungal cultures of skin biopsies may be necessary to rule out differential diagnoses.
8.2 Pneumonia
Wombats are prone to lower respiratory disease, including bacterial and fungal pneumonia. Clinical signs are variable and can include inappetance, lethargy, coughing, nasal discharge and tachypnoea. Organisms that have been implicated in clinical cases include Pseudomonas sp., Actinomyces sp., Serratia odorifera, Escherichia coli and Emmonsiellopsis sp. (Ladds 2009; Schaffer-White et al. 2017; ARWH 2018; Danesi et al. 2020; Hung et al. 2020; Crosta et al. 2022). Conventional radiography and/ or CT (Fig. 37.1a) and tracheobronchial/bronchoalveolar lavage are valuable diagnostic tools in suspected cases of bacterial pneumonia. Direct tracheal sampling with a guarded sterile swab via endoscope guidance has also been described in juvenile wombats (Crosta et al.
2022). Treatment consists of a protracted course of appropriate antibiotics (nebulised and/or systemic), together with general supportive care. The prognosis is poor if disease is advanced (Fig. 37.1b). Adiaspiromycosis is difficult to diagnose antemortem because the causative fungus (Emmonsiellopsis sp.) is challenging to culture; however, lung histopathology or PCR is definitive. Aspiration pneumonia is a recognised problem in very young or debilitated hand-reared wombats (see Chapter 15).8.3 Dental disease
Acquired dental disease is common in wombats in managed care maintained on an inadequately abrasive diet, primarily because of their hypsodont and elodont dentition. Malocclusion also occurs in juveniles secondary to poor hand-rearing technique and/or trauma (Bryant and Reiss 2008; Hulst et al. 2015). Although most cases of dental disease are associated with husbandry deficiencies, lingual cheek teeth spurs have been observed in free- ranging northern hairy-nosed wombats (T Portas pers. comm.).
Fig. 37.1. Adult bare-nosed wombat (Vombatus ursinus) with an 8-wk history of lethargy and weight loss. (a) Axial CT image of the thorax. Multifocal alveolar disease primarily affecting the right caudal lung lobe can be seen, with a large bulla present at the lateral margin. (b) Gross necropsy examination of lungs. Pyogranulomatous pneumonia with abscessation caused by Actinomyces hyovaginalis infection was diagnosed. Images: Taronga Western Plains Zoo
Early detection of dental disease is important because progression can be slowed when appropriate and timely treatment is instituted. Coronal reduction and removal of spurs can be achieved with low-speed dental burrs (see Chapter 13).
Regional nerve blocks can be used to augment systemic analgesia for oral or dental surgery. Wilson and Gillett (2010) administered 0.25 mL bupivacaine bilaterally to achieve a mandibular block in a southern hairynosed wombat after first identifying the mandibular foramen on a reference skull.
The mandibular foramen is approached medially and the mental foramen for rostral mandibular surgery is generally approached laterally. It should be noted, however, that the bare-nosed wombat has multiple mental foramina (one rostral to the premolar and one or more ventral to the incisors) (Saber 2015).Unilateral or bilateral commissurotomy can be undertaken to improve access to the wombat oral cavity for advanced dental procedures (Wilson and Gillett 2010) (see Chapter 10).
8.2 Syndromes of uncertain aetiology
Hyperostosis has been reported in two zoo-housed male bare-nosed wombats. Generalised cortical thickening was identified in the skeleton of a deceased 13-yr-old individual with either a genetic or diet-related metabolic aetiology considered most likely (Slon et al. 2014). The other case (a 5-yr-old) had metastastic calcification in the thorax and trachea alongside the bone changes (L Vogelnest pers. comm.). A definitive cause was not determined but differential diagnoses included excess dietary vitamin D, a metabolic disorder and toxicity such as ingestion of calcinogenic glycoside-containing plants.
Osteodysplasia and suspected endocrinopathies have been seen in hand-reared wombats. Proportionate dwarfism in a 2-yr-old 1.93-kg male bare-nosed wombat was associated with growth plate abnormalities, possible pituitary acidophil/basophil hypoplasia and secondary infections (ARWH 2018 case no. 7702) (Fig. 37.2). A 2-yr-old 13.9-kg female bare-nosed wombat with lipid keratopathy, chronic skin and dental issues and generalised poor growth had an unusually shaped, mildly hypoplastic pituitary gland and moderate bilateral corticomedullary adrenopathy identified at necropsy (ARWH 2018 case no. 10819). Questionable thyroid function and significant concurrent GI infections suggestive of debilitation and immune compromise were noted in both cases.
Other conditions described in individual wombats include skeletal myopathy (ARWH 2018 case no. 5068), encephalomalacia (ARWH 2018 case no.
3778), hyperparathyroidism associated with osteopenia (ARWH 2018 case no. 2361), chronic papillomatous cheilitis (ARWH 2018 case no. 7810) and assorted nephropathies (ARWH 2018 case nos 1056, 1663, 2361, 5910 and 6686).
Fig. 37.2. Two 2-yr-old hand-reared bare-nosed wombats (Vombatus ursinus): one diagnosed with suspected pituitary dwarfism (foreground), the other clinically healthy with a history of normal growth. The dwarfism was associated with growth plate abnormalities and immune compromise. Photo: Suzanne and David Alder
8.3 Toxicities
Like other herbivores, wombats are at risk of exposure to plant toxins (see Chapter 19). A cluster of cases of alopecia, dermatitis and poor body condition in young southern hairy-nosed wombats was shown to be associated with hepatotoxicosis. Pyrrolizidine alkaloids were suspected, with ingestion of toxin-containing plants thought to be related to foraging in a degraded habitat (Woolford et al. 2014).
Glucosinolate toxicity, secondary to summer grazing on alien invasive plants, was the suspected cause of a cluster of hepatopathies in southern hairy-nosed wombats from one site in SA (Camp et al. 2020).
Wombats recolonising disused rehabilitated mine sites may be exposed to heavy metal contaminants via ingestion of grasses and substrate but the potential health impacts have not yet been thoroughly investigated (Penrose et al. 2022).