Causes of mortality and morbidity in the endangered southern brown bandicoot (Isoodon obesulus obesulus)

Abstract

The southern brown bandicoot (Isoodon obesulus obesulus) is a small, endangered, Australian, ground-dwelling marsupial. Apart from isolated necropsy reports, there has not been a systematic investigation into the health and causes of death for this species.

Objective: To investigate and document the causes of death and the parasites of free-ranging populations of southern brown bandicoots in southern, central Victoria, Australia.

Methods: Gross necropsy, histopathology and identification of ectoparasites and endoparasites were performed on 62 dead southern brown bandicoots opportunistically collected from July 2011 to January 2018. Molecular methods were used to detect and genetically characterise the presence of Toxoplasma gondii in select tissues.

Results: The vast majority of animals died as a result of either motor vehicle trauma or predation (45/62). A further seven bandicoots died from varying causes with either diagnostic gross or microscopic evidence of pathology, and there were five ejected pouch young. The cause of death was undetermined in another five cases. Toxoplasma gondii was detected in one southern brown bandicoot, which demonstrated polymorphisms in the B1 and SAG3 genes. This is the first definitively documented case of T. gondii infection in this species in Victoria. All of the identified parasites have previously been reported in southern brown bandicoots, apart from a metastrongyloid lungworm, which is reported here for the first time.

Conclusions: Motor vehicle trauma and predation are highlighted as causes of fatality that likely threaten these populations of southern brown bandicoots. Further investigation into the role that disease, particularly toxoplasmosis, may be playing in southern brown bandicoot population decline is recommended.

Keywords: ectoparasites; endoparasites; necropsy; pathology; southern brown bandicoot; toxoplasmosis.

Figure 1

Light micrographs of helminths from opportunistically necropsied southern brown bandicoots (Isoodon obesulus obesulus) from southern Victoria. (A–C) Labiolura inglisi in large intestine of W 411–16 (10× magnification); thin arrows indicate alae and fat arrow indicates transverse section of oesophagus. (D–F) Cross‐sections of metastrongyloid lungworm(s) surrounded by necrotic lung in W 1006–16 (D) ×10; (E, F) (×20), arrow indicates worm cuticle; (G) cross‐section of Eucoleus longiductus in tongue of W 517–17 (20×); (H) cross‐section of a trichostrongyloid nematode found on tongue surface of W 1008–16 (40×). Black bar represents 1 mm in all micrographs other than (H) where it represents 0.5 mm.

Figure 2

Light micrographs of internal parasites in opportunistically necropsied southern brown bandicoots (Isoodon obesulus obesulus) from southern Victoria. Klosiella quimrensis in renal medullary tubules (arrows pointing to organisms): (A) from W 1117 to 17 (×10 magnification); (B) W 1117 to 17 (×20); (C) from W 434 to 16 (×20); (D) from W 434 to 16 (×40). Mackerrastrongylus mawsonae from W 517 to 17 embedded in glandular tissue of small intestine: (E) Note parasite is surrounded by an inflammatory reaction and necrotic tissue destruction, near junction between lamina muscularis (top left corner) and glands in submucosa (lower right corner) (×20); (F) ×40. Black bars indicate 1 mm in (A–E), and 0.5 mm in (F).