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Proceedings of the First Symposium on Marsupials in New Zealand

Introduction

Introduction

Tuberculosis is caused by acid-fast bacilli in the genus Mycobacterium, principally by M. tuberculosis, M. bovis and M. avium (the human, bovine and avian strains respectively).

Although recognition of tuberculosis in wild brushtail possums Trichosurus vulpecula is a relatively recent event, tuberculosis in captive animals has been recognised for sixty years. Moore (1903) noted "an enlargement of one of the stifle joints exactly in the nature of a strumous enlargement or abcess sometimes found in sheep. Post-mortem examination showed the lungs one mass of tubercles." These lesions were seen in 1895 in a young possum held in captivity. Subsequently tuberculosis was reported in a possum held in a zoological park (Scott 1928).

Tuberculosis in wild possums was first reported in 1970 (Ekdahl et al. 1970), and this report was an outcome of a growing awareness of an association between the persistence of tuberculosis in cattle in a tuberculosis control area and tuberculosis in possums in the same environment. The distinctive lesions of tuberculosis due to Mycobacterium bovis in the possum have been described page 164 (Ekdahl et al. 1970, Smith 1972) and Smith (1972) drew attention to the large numbers of organisms which may be present in these lesions.

There is now compelling circumstantial evidence linking tuberculosis in possums to a high and persistent reactor rate in cattle sharing the same environment and, although a number of feral or wild species may be infected with M. bovis, only the tuberculous possum appears to have attributes of a significant reservoir of infection for cattle (Animal Health Division 1976).

The susceptibility of the possum to M. tuberculosis and M. bovis infections has been established experimentally (Bolliger and Bolliger 1948). Intraperitoneal and intramuscular injections of tubercle bacilli resulted in death in 2 to 5 weeks and natural transmission of M. bovis from an experimentally infected possum to a cage mate was demonstrated.