Viruses of the common brushtail possum (Trichosaurus vulpecula) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science, Massey University, 1998
A tissue culture survey was conducted to detect viruses in possums. Up to 14 tissues from 93 wild caught possums were inoculated (co-cultivation) onto three marsupial cell lines. Possum primary cell cultivation was also developed throughout the survey period and together these procedures sought to detect viral infections as overt clinical disease, as unapparent illnesses or present in a latent form. Three passages of seven days duration were routinely performed. Haemadsorption tests (chick, guinea pig and human "O" RBCs at 37°C) and examination of stained monolayers (chamber slides) were completed for the third passage. A few adenovirus-like particles were identified by electron microscopy in one of two possums' tissue cultures in which a non-sustainable cytopathic effect was detected. No haemadsorption or abnormal chamber slide cytology was demonstrated. Adenoviruses were identified by electron microscopy in faecal or intestinal contents samples from four of the survey possums. Wobbly possum disease (WPD), a newly described neurological disease of possums, was suggested to have a viral aetiology when filtered infectious material (clarified spleen suspension from a confirmed case of WPD passed through a 0.22 μm membrane) could transmit disease to susceptible possums following intra-peritoneal inoculation. Preliminary studies into routes of transmission of WPD used a standardised tissue suspension prepared from pooled infected liver, spleen and brain tissue. Titration of the tissue suspension in vivo demonstrated in excess of 10 5 possum infectious doses per ml. Clinical signs associated with neurological disease were confirmed by the presence of characteristic histological lesions and a scoring system was devised to assist diagnosis. The tissue suspension was shown to cause disease when inoculated by the gastric, tracheal, intradermal (ID) and intraperitoneal (IP) routes. Blood and urine from infected possums were shown to be infectious when inoculated by the ID and IP routes respectively Disease was transmitted by a suspension of blood feeding mites (Trichosurolaelaps crassipes) injected intradermally however the transfer of live mites from an infected possum to a non-infected recipient failed to transmit WPD. Sentinel control possums housed adjacent to experimentally infected possums did not develop WPD but when two inoculated possums were placed in group housing with five in contact controls, all possums became infected. The absence of aerosol transmission to non-contact control possums suggests that transmission requires direct contact between possums or contact with a contaminated environment. Naturally occurring transmission was demonstrated to be feasible by the cloacal / oral and intradermal routes. Further work is required to determine the relative importance of these routes under natural conditions. A neurological disease syndrome was investigated in a wild possum population in the Rotorua district and determined to be almost identical to WPD. Comparison of the Rotorua syndrome and WPD together with histological evidence for more widespread distribution of similar disease processes suggest that WPD or variants may already be distributed throughout New Zealand. As such, WPD may be a newly recognised disease rather than a newly emergent disease. Papillomavirus particles were detected in association with wart-like papillomas on the tail of a possum. A papillomavirus specific product was amplified by PCR and manually sequenced. Sequence comparisons and phylogenetic analysis determined a new papillomavirus type (possum papillomavirus). The survey methodology and the possum viruses described in this thesis are discussed in terms of identifying suitable viruses for use as biological control agents.