NON-INFECTIOUS DISEASE
Neoplasia and toxicoses are covered in Chapters 18 and 19 respectively.
2.1 Renal disease
Progressive renal disease was a significant cause or contributing factor in the death of mountain pygmy-possums in managed care (Scheelings and Dobson 2015).
Of 48 necropsy reports, 17 (35.4%) animals were suffering some degree of renal impairment. The mean age of the affected animals was 6 yr and no obvious aetiology was detected. Metastatic mineralisation was a common sequela to renal disease, with one animal diagnosed with secondary renal hyperparathyroidism in this case series. Renal disease was a frequent finding in a review of post mortem records of Leadbeaters possums held in managed care, with chronic nephropathy the most common condition identified (Steventon et al. 2023). Idiopathic bilateral hydronephrosis has been reported in an adult male sugar glider that died after presenting with acute abdominal distension (Cusack et al. 2016).2.2 Eastern ring-tailed possum caecal dysbiosis/stasis syndrome
Ring-tailed possums (Pseudocheirus spp.) are folivores consuming primarily Eucalyptus leaves. They are caecal hind-gut fermenters and rely on caecotrophy to meet their daily fluid, protein, nitrogen and energy needs from a low nutrient diet. This digestive strategy relies on a healthy caecal microbial flora, the disruption of which results in a syndrome of caecal dysbiosis and stasis. It is more commonly seen in juvenile and sub-adult ring-tailed possums but may also occur in adults. The aetiology and pathogenesis of caecal dysbiosis/stasis syndrome are poorly understood, however, high carbohydrate, fruit-based diets and the use of some antibiotics are known predisposing causes (Johnson and Hemsley 2008; Chapter 11; Chapter 14; L Marr pers. comm. 2021; Davies and Vogelnest in press). Caecal stasis is frequently seen in hand-reared weanling ring-tailed possums when transitioning from a milk to solid diet.
It is essential to introduce a primarily folivo- rous diet to establish a normal caecal microbiome and function at weaning. The clinical signs can be insidious and subtle and include poor coat condition; poor weight gain; low body condition; increased hunger and thirst (often associated with restlessness and frantic behaviour); soft doughy abdominal distension (impaction of the caecum with fluid and leaf particles with minimal gas); small, round, dry faecal pellets; and lack of production of caecotrophes. In advanced stages significant but not tympanic abdominal distension, emaciation (muscle wastage), low faecal pellet count, colic, lethargy, weakness, hypo- proteinaemia, anaemia, shock, and death are seen. Tympanic abdominal distension (or bloat) where the gastrointestinal tract is filled with a mixture of fluid content and gas (in extreme cases predominantly gas) is more commonly seen in sub-adult or adult ring-tailed possums. This may be associated with antibiotic (and sometimes dietary) induced dysbiosis and stasis, but other causes such as obstruction (torsion, intussusception) or bacterial or yeast gastroenteritis/typhlocolitis are also likely differentials (L Marr pers. comm. 2021; Davies and Vogelnest in press).Diagnosis is based on history and clinical signs. Imaging (radiography, ultrasound) is useful, particularly to distinguish caecal dysbiosis/stasis from other causes of abdominal distension (Davies and Vogelnest in press). Radiographically the very large caecum dominates the abdominal image, obscuring other abdominal organs. In the normal ring-tailed possum, the content is primarily digesta interspersed with small pockets of gas. In addition, the viscera cannot be distinguished easily because the absence of abdominal adipose tissue results in positive silhouetting of adjacent viscera, camouflaging their serosal surfaces (Vogelnest and Allan 2015; Davies and Vogelnest in press). Abdominal distension with minimal to moderate amounts of gas is suggestive of caecal dysbio- sis/stasis syndrome.
Large accumulations of gas, with or without distension may be seen with antibiotic induced dysbiosis, obstruction or gastroenteritis/typhlocolitis, particularly in adults.Treatment of caecal dysbiosis and stasis is aimed at re-establishing hydration, energy balance, normal gut motility and microbiome. This is achieved through provision of supportive care (fluids, high fibre and protein critical care diets, use of prokinetics, pre- and probiotics, transfaunation, and correcting diet and husbandry (Johnson and Hemsley 2008; Chapter 14; Appendix 4; L Marr pers. comm. 2021). Early recognition is critical to successful treatment. Euthanasia is recommended in advanced cases. Prevention is based on provision of an appropriate diet and conservative and judicious use of antibiotics (Chapter 14; Appendix 4).
2.3 Necrotic tail syndrome and tail trauma
A syndrome of superficial dermatitis progressing to deep tissue infection and tail necrosis was observed in a population of zoo-housed eastern ring-tailed possums. Lesions started as small breaks in the surface of the skin, progressing rapidly to involve the muscles and tendons of the tail. In many instances the tail became necrotic because of obliteration of blood vessels, leading to ischaemic damage necessitating amputation. Although advancement of wounds could be slowed by covering the lesions with bandaging to prevent self-trauma, this was not always successful in limiting spread. Culture of lesions did not identify any obvious pathogens. Histological examination of affected tails revealed superficial to deep ulceration with a mixed inflammatory response and mild contamination with surface bacteria. In some cases, microfractures within the caudal vertebrae were observed. The tail lesions were observed in possums housed both indoors and outside, at the same time of year and in no cases was there a history of trauma. Treatment with anti-inflammatory drugs and antibiotics (both topical and systemic) was of limited use in managing the disease.
Tail tip trauma is seen in eastern ring-tailed possums in managed care (zoo and rehabilitation) housed in pairs or groups in the same enclosure and those housed in outdoor aviary type enclosures. Trauma is the result of bites from conspecifics within the same enclosure or from free-ranging possums on the outside as they curl their tails through the wire of the enclosure. Injuries include mild to severe skin lacerations, muscle and tendon damage and occasionally vertebral fractures. Without early intervention, infection (including osteomyelitis) and progressive necrosis may result. Aggressive treatment with antibiotics, anti-inflammatory/analgesic drugs, debridement, bandaging and occasionally amputation (zoo animals) or euthanasia (rehabilitation animals) is indicated (L Vogelnest pers. comm.).
2.4 Fate of hand-reared juvenile possums
In a recent study aimed at assessing the short-term survival of hand-reared juvenile common brush-tailed possums, 20 individuals (10 male and 10 female) were radio-tracked for up to 40 d post release. The investigators found that eight possums (40%) survived until the end of the study, nine (45%) were killed by foxes or had to be returned to care, and three (15%) had unknown fates (Mella et al. 2023). At the completion of the study it was concluded that individual possums that displayed more exploratory behaviour and that were less habituated to humans had a greater chance of survival, regardless of whether they were hard or soft released (Mella et al. 2023). This investigation highlights the need for establishing evidence-based practices for rehabilitation of native Australian marsupials.
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