CASE NOTES


DEVIL FACIAL TUMOUR DISEASE

Benn Bryant, Senior Veterinarian, Taronga Western Plains

Posted Flock & Herd March 2011

Abstract

Devil Facial Tumour Disease (DFTD) was first recognised in free ranging Tasmanian devils (Sarcophilus harrisii) in the north-east of Tasmania in 1997. The disease subsequently spread and now occurs over much of eastern Tasmania. To date, DFTD has accounted for a decline in devil numbers by over 50% from an estimated 150,000 in the mid 1990s. At the current rate of spread, it is predicted that Tasmanian devils will be extinct in the wild by 2030. Accordingly, Tasmanian devils are now classified as endangered by the IUCN.

This neoplastic disease is rare in animals less than 2 years of age and is characterised by the development of firm, rapidly growing, locally invasive, ulcerative soft-tissue tumours affecting the head and neck.[1] The incubation period is up to 12 months and death, usually due to inanition, supervenes within 6 months of first appearance of lesions. Histologically the neoplasms are located in the facial dermis or oral submucosal connective tissue and are composed of multinodular proliferations of poorly differentiated round cells.[2] Metastases occur in over 50% of cases. Initial immunohistochemical studies suggested the tumours were of neuroendocrine origin.[3] More recently, molecular studies have revealed DFTD cells to be of Schwann cell origin.[4]

The transmissible nature of DFTD was evident from early observations of the movement of the disease through free-ranging devil populations but there was no evidence for the presence of potentially oncogenic microorganisms on histopathology or by transmission electron microscopy.2 Instead, the discovery that tumour cells from different individuals share an identical karyotype provided strong evidence that mode of transmission is by direct infection with neoplastic cells of the same cell line.[5] Molecular studies have revealed that the Tasmanian devil population is relatively homozygous particularly in the region of the immunologically important major histocompatibility complex (MHC). In effect, Tasmanian devils are immunological clones with limited ability to recognise and reject DFTD cells. Consequently, DFTD cells implanted into bite wounds from affected individuals into naive individuals during aggressive courtship and mutual feeding encounters behave as well-tolerated allografts.

By 2002, significant population declines were being identified and concerns for the survival of the species raised. A national response to the threat, The Save the Tasmanian Devil Program, was established in 2003 with a mandate to investigate DFTD and identify management options.[6] The Australian Federal and Tasmanian State governments, overseen by a steering committee and co-ordinated by the Tasmanian Department of Primary Industries, Parks, Water and Environment (DPIPWE), fund the Program. As part of this role, DPIPWE facilitates and supports research and contributions from a number of organisations including fauna parks and zoos. The Program has four areas of focus; population monitoring, laboratory investigation of the disease, development of methods for ameliorating the impact of DFTD on wild populations and establishment and management of a captive 'insurance' population of disease free devils.

The insurance population is held across a number of zoos and fauna parks in Australia. It is managed cooperatively under the auspices of Zoos and Aquaria, Australia (ZAA), the regional zoo industry's professional body, via a centralised studbook with the goal of retaining maximal genetic diversity over time. In January 2010 there were 277 individual devils enrolled in the insurance population. This includes 28 animals held at Taronga Western Plains Zoo.

 


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