Biology and medicine of marsupials (Proceedings)

Marsupials have some of the most unique anatomic and physiologic features among members of the Class Mammalia. Many of these features are well-grounded, as marsupials are one of the oldest groups of mammals in existence. A review of these features will be discussed in this presentation.

In recent years, marsupials have become popular as pets. Unfortunately, many of these animals are acquired because of their novelty, and pet owners soon lose interest or realize that they cannot meet the specific needs of their pet. Meeting the specific needs of these animals can be difficult, as the literature regarding their captive requirements is relatively sparse or based on anecdotal reports. The secondary purpose of this presentation is to provide veterinarians with a review of the literature that is available regarding the specific care and medicine of captive marsupials.

The Virginia opossum (Didelphis virginiana) is the only native species of marsupial in the United States. The opossum is found throughout the United States, except in extreme montane and desert regions. This species is generally regulated by state wildlife and fisheries agencies and persons possessing these animals should have appropriate permits. Veterinarians are allowed to treat opossums presented to their facility for emergencies, but should transfer them to a wildlife rehabilitator once the animal is stabilized.

Opossums are generally short-lived (2-5 years). In captivity, these animals have been reported to survive greater than 5-10 years, but these cases are rare. Being a marsupial, these animals have a pouch. Sexual maturity is achieved in approximately 7-9 months.

Opossums are omnivorous, and these animals have a voracious appetite. Juvenile opossums can be raised on a canine formula. As the animals begin to wean, they should be offered a commercial canine ration with fruits, vegetables, and invertebrates. Opossums that are offered lean meat exclusive diets often develop secondary nutritional hyperparathyroidism. Opossums should be provided free choice water.

Marsupial case management should follow standard protocol for mammals. Blood samples may be collected from the ventral tail vein or jugular vein. Hematologic profiles are generally consistent with other mammalian species. Fecal examinations should be performed to assess the animal for endoparasites. Because of the rather "trashy" lifestyle of these animals, parasite burdens are generally high. The author generally prescribes metronidazole for protozoa, praziquantel for cestodes, and fenbendazole or ivermectin for nematodes. Ectoparasites should be removed to reduce the risk of zoonotic disease transmission. The author has used both Frontline and Advantage in opossums without adverse effects. Diagnostic imaging can be used to assess skeletal injuries or visceral changes. Microbiological testing for both bacteria and fungi should be pursued when warranted.

For wild opossum cases, traumatic injuries are the most common presentation. A thorough physical examination and appropriate diagnostic tests should be performed to assess the patient. Coaptation or orthopedic surgery should be pursued to correct any fractures. Pyovaginitis is a common occurrence in captive female opossums. An ovariohysterectomy should be done in affected animals. Bacterial gastroenteritis and pneumonia are also common findings in captive opossums.

Treatment plans for opossums should follow similar protocols established for other non-marsupial mammals, although these animals do have a lower metabolic rate than more advanced mammals and may require lower dosing regimens than similarly sized non-marsupial mammals. Several published reports of anecdotal dosing regimens exist and these will be discussed during the presentation.

The sugar glider (Petaurus breviceps) is a marsupial with a range that includes Australia, Indonesia, and New Guinea. Sugar gliders have become very popular in the United States because of successful captive-breeding programs, although wild-caught animals are also routinely sold. Wild-caught animals are more likely to have parasites and complications adapting to captivity. Always recommend that your clients seek captive-born specimens.

An understanding of the unique anatomical features of these animals will provide insight into their behavior and specific needs in captivity. The sugar glider is a nocturnal species with large laterally positioned eyes. Gliders are arboreal species that have scimitar-shaped claws and fused 2nd and 3rd digits ("comb") to help with climbing. Gliding is achieved by the extension of their patagium, which are skin fold extensions off their lateral body wall. The sugar glider tail is also used as a stabilizer during "gliding". The reproductive system of the sugar glider is similar to that described in other marsupials: female- pouch, uterus bicornuate; male- bifurcated penis.

Sugar gliders are omnivorous. In the wild, their diet consists of a combination of animal (arthropods) and plant products (eucalyptus phloem sap, manna, honey dew, nectar and pollen). In captivity, there are a variety of commercially available food items that can be used to accommodate the nutritional needs of these animals. A diet used successfully to raise captive sugar gliders is a (1:1) Leadbeater's mixture (150-ml warm water, 150-ml honey, one shelled hard-boiled egg, 25-g high protein baby cereal, one tsp. multivitamin) and a commercial insectivore diet (Mazuri Brand, St. Louis, MO). Live foods, such as crickets, mealworms, and waxworms, can also be offered, but should be provided a commercial "gut-loading" diet to insure their nutritional value. Plant products, such as diced apples, grapes, mango, carrots and sweet potato, will also be readily accepted. Sugar gliders are prone to obesity and their weight and a dietary intake should be monitored closely.

These small marsupials should be provided an enclosure that provides ample height. Providing "climbing" room will allow these animals to exercise and reduce the likelihood of becoming obese. The enclosure should be full of climbing branches and a have a nest or hide box. If these animals are not provided an area to hide, or they are forced to spend time on the ground, they will become stressed and potentially immunocompromised. A newspaper or recycled paper substrate can be used in the bottom of the enclosure and will allow the owner to monitor fecal and urine production.

The most common problems reported in sugar gliders include secondary nutritional hyperparathyroidism, parasites, and bacterial enteritis. Secondary nutritional hyperparathyroidism commonly occurs in animals offered nutritionally deficient crickets and fruits. Animals often present with generalized weakness, muscle tremors, and pathologic fractures. A thorough history, physical examination and radiographs can be used to confirm a diagnosis. These cases should be considered emergencies and treated with appropriate supportive care (fluids and enteral support) and calcium supplementation. Endoparasites are routinely identified in wild-caught specimens. A fecal float and direct smear should be performed on new patients. Bacterial enteritis is routinely diagnosed in poorly managed sugar gliders. Animals maintained on an inadequate diet and that are under constant stress (e.g., excessive handling, inappropriate enclosure, temperature fluctuations) often present with watery diarrhea. A complete blood count, fecal float, and fecal culture and sensitivity should be performed. The animals should be provided supportive care and enrofloxacin (5mg/kg PO BID) (Baytril, Haver/Diamond Scientific, Shawnee Mission, KS) while the culture and sensitivity are pending. Salmonella sp. can be isolated from clinically normal animals, and clients should be warned of the zoonotic potential when keeping these animals.