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Item An Australian abroad : the secret life of the brushtail possum (Trichosurus vulpecula) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, Manawatu, New Zealand(Massey University, 2016) Richardson, Kyle StephenThe “superspreader” hypothesis relates disease transmission to social contacts and assumes transmission is driven by the frequency, type and distribution of contacts among infected and susceptible individuals. I investigated characteristics of brushtail possum (Trichosurus vulpecula) home ranges for six wild free-living subpopulations, (four grids were studied; all of them before possum depopulation and two of them after possum depopulation) constructing social networks relevant to bovine tuberculosis (TB) transmission before and after depopulation. I also experimentally infected possums with a novel strain of TB to monitor secondary case infections in relation to these contact and other factors, including population density and sex ratio. Before depopulation home range estimates showed adult males had larger home ranges than female and younger possums. Home range overlap and area of overlap differed between subpopulations, and possum sex and age; with adult males having more and larger overlaps with other possums. Possums were fitted with proximity-logging collars and contacts registered between April and October, 2012. The number of connections an individual has with others and the probability of the distribution of contacts it has within the population, or node degree and betweenness, also known as the shortest distance between individuals, were associated with sex, with males having higher values for each. Males also contacted more possums than females. Post-depopulation results showed an influx of male possums, higher population density, and smaller home range sizes than before depopulation. Possums post-depopulation also lacked an apparent ‘routine’ in contact networks, interacting with other possums haphazardly. The greater level of contact among adult males, than before depopulation, and their effects on recovering populations post-depopulation, was likely the cause of more TB infection in adults and males. This thesis provides empirical evidence that adult male possums have home range and contact network characteristics that are likely to enhance their involvement in the transmission and persistence of TB, relative to female and younger possums. Observations of experimentally infected individuals showed that infected males survived longer than females and that, as a consequence, those males potentially acted as a “supershedding” subgroup. I therefore provide evidence that adult male possums are the most important drivers of TB transmission and persistence of infection in populations, and could be targeted for control measures.Item The behaviour, pathophysiology and pathology of brushtail possums (Trichosurus vulpecula) poisoned with 1080 or brodifacoum, and the implications for possum welfare : a dissertation presented in partial fulfilment of the requirements for the degree of Ph.D in Physiology at Massey University, Palmerston North, New Zealand(Massey University, 2004) Littin, Kate ElizabethMillions of brushtail possums (Trichosurus vulpecula) are poisoned yearly in New Zealand owing to damage caused to agriculture and the environment. They are nonetheless sentient animals capable of suffering, and legislative and ethical obligations, and public concern demand that only the most humane poisons are used (Chapter 1). Accordingly, the aim of this work was to evaluate the effects of two poisons used for killing possums in New Zealand, 1080 and brodifacoum, and the implications for animal welfare. Animal Ethics Committee approval was obtained for all work. A lethal dose of 1080 in carrot baits caused retching, vomiting and seizures in possums caged indoors (Chapter 2). Possums did not fully lose consciousness until death but were likely to have been in a reduced state of awareness beforehand. The first signs of poisoning were observed after an average of nearly 2 h and they died on average 11.5 h after consuming baits, giving a period of potentially reduced welfare of approximately 9.5 h. Six possums of eight that consumed a sublethal dose showed signs of sickness, indicating that some sublethal doses can reduce welfare. Alphachloralose (a sedative) and paracetamol (an analgesic) had no effect on the behaviour of caged, 1080-poisoned possums (Chapter 3). The consumption of 0.88 mg/kg brodifacoum in cereal pellet baits by caged possums caused widespread haemorrhages which may have led to weakness, sickness or pain (Chapter 4). Possums did not lose consciousness until death after an average of 21 days but were likely to have been in a reduced state of awareness for up to six days beforehand. Signs of poisoning were first seen after 14 days on average, meaning welfare was potentially reduced for about seven days. Following the consumption of 0.86 mg/kg brodifacoum in cereal pellet baits, blood clotting ability was reduced and all possums had internal haemorrhages, both within eight days of bait being offered (Chapter 4). Possums penned outdoors with space for a high level of activity and exposure to spring and summer weather died after a lethal dose of 1080 or brodifacoum at about the same times as possums caged indoors, and following similar preceding signs of poisoning (Chapter 5). This implied that the second-most humane poison for possums and that broadifacoum is among the least humane (Chapter 6).Item Behavioural patterns of possums and cattle which may facilitate the transmission of tuberculosis : a thesis presented in partial fulfilment of the requirements for the degree of Master in Veterinary Science at Massey University(Massey University, 1993) Paterson, Brent MaynardBehavioural patterns of a population of Australian brushtail possums with endemic tuberculosis were studied using radio telemetry, and by direct observational techniques, from November 1990 to April 1992. The study area, on the east coast of the Wairarapa, New Zealand, allowed observations of interaction between the major wildlife vector of tuberculosis in New Zealand, and cattle run as part of a commercial farming venture. The rugged 40 ha study area is mainly covered in 2-10 m high scrub, with patches of native bush and some large trees. Part of the area has been cleared of scrub and grassed. Poorer quality pasture is also available in small pockets in many other areas of the paddock. Possums had distinct ranges that remained constant over the duration of the study period, and ranges of many possums overlapped. Males had significantly larger ranges during the breeding season, and had the largest ranges overall. The area covered by a possum in a night’s activities varied considerably between possums, and often for an individual over consecutive nights. There were no significant differences between home ranges of tuberculous and non-tuberculous possums, although there were indications that the size of nightly activity areas of the former decreased as the disease progressed. Twenty-five juvenile possums were followed over 8-10 months, 2 dispersed from the area, and 7 died within their natal home range. Most of the juveniles died from starvation and exposure. Interactions between possums and cattle were observed in a natural setting, and also by introducing sedated possums to the same area to simulate terminally-ill tuberculous animals. Possums spent a variable amount of time feeding on pasture in the 40 sq.m observation area, ranging from a few minutes, to several hours. Normally possums appeared to avoid cattle whenever possible, and if necessary climbed trees to get away. The activities of several debilitated possums are described and their apparent indifference to external influences - in particular time of day - noted. The intense interest shown by cattle in sedated possums is described, and the possibilities for transmission of tuberculosis from possums to cattle discussed. It is concluded that transmission of tuberculosis is unlikely to occur on open pasture under normal circumstances, but that sick tuberculous possums, and later their carcases, are a source of infection. Tuberculosis in English badgers is compared, and contrasted, with the situation in New Zealand. Possible explanations for the absence of the disease in Australian wildlife are discussed. The differences in habitat and population density are suggested as the main reasons for the variations between, and within, countries. The importance of controlling tuberculosis in New Zealand, deficiencies in present control systems and possible areas for future research are outlined.Item Bovine tuberculosis in the Brushtail possum (Trichosurus vulpecula) : behaviour and the development of an aerosol vaccinator : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science at Massey University(Massey University, 2001) Norton, SolisThe Australian brushtail possum (Trichosurus vulpecula) is a wildlife reservoir of tuberculosis (Mycobacterium bovis) in New Zealand. The disease is endemic over one third of the country. Possum control operations have reduced the prevalence of disease in livestock but have not fully controlled infection in wildlife or geographic spread of the disease. The disease is transmitted to livestock when they investigate the unusual behaviour of terminally ill possums. Reduction of disease incidence in possums through vaccination with bacille Calmette-Guerin (BCG) has shown promise both in pen trials and field studies. Integration of vaccination into existing control programmes may reduce transmission of tuberculosis among possums, and from possums to livestock. There are two parts to this thesis. Part one is a longitudinal, behavioural study of tuberculous and nontuberculous wild possums. Part two is a description of an aerosol delivery device (aerosol vaccinator) designed to administer aerosolised BCG vaccine to possums in the wild, and a record of its progressive development. The aim of part one was to identify aspects of behaviour of tuberculous possums that may influence disease transmission to livestock. Twenty two tuberculous and eight healthy possums were observed. Possums were radio tracked weekly and live trapped at bimonthly intervals on a 56 hectare site in the Wairarapa, New Zealand. Generally possums remained within their activity range apart from infrequent long distance forays. Possums were weak, lethargic and uncoordinated during the terminal stages of disease which lasted for one to three weeks. Only three possums made long forays when terminally ill with tuberculosis. The carcasses of 17 tuberculous possums were recovered of which 15 were in dense scrub or on long grass under scrub and two were on pasture. Of these 17 carcasses, 14 were within or near (<200m) to their activity range. Most tuberculous possums died in their activity range and in scrub. These possums represent little risk of infection to livestock, but a risk to other wildlife. However, the small number of tuberculous possums that died on pasture present an important risk to livestock. Interactions between diseased and healthy possums during long distance forays may cause considerable geographical spread of tuberculosis. Part two, the development of an aerosol vaccinator, consisted of pen and field trials. The aim of pen trials was to evaluate the willingness of possums to investigate novel objects and the influence of social hierarchy on this investigative behaviour. It also allowed refinements to aerosol vaccinator design. Four captive colonies were used. In each colony most possums (80%) showed minimal neophobia and would actively investigate novel objects. A small proportion (20%) would not approach a novel object. A loose social hierarchy existed with one dominant animal and a changeable middle order. In two of the four colonies, there was one possum clearly at the bottom of the social order. Social hierarchy did not affect the proportion of a colony which could investigate a novel object or vaccinator. However it did effect the order in which individual possums would investigate. The aim of the field trials was to evaluate the efficacy of an aerosol vaccinator with possums in the wild. During five field trials, the proportion of the possum population marked with dye from the device steadily increased and ranged from 0%–34%. Trials were conducted over eight months and during this period a total of 56% of the study population was marked with dye. Some possums would repeatedly use a vaccinator. These results justify further research into aerosol vaccination of wild possums with BCG. Three key avenues for future research include determining the proportion of a possum population which will use the device, developing an aerosol container suitable for dispensing BCG vaccine and determining whether the combination of vaccinator and aerosol vaccine elicits a protective immune response. The aerosol vaccinator may be use [sic] to deliver aerosolised materials other than BCG to possums. It may also be altered to suit use by other species.Item Two studies on the control of wildlife-derived tuberculosis : farmer views and model validation : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Studies in Epidemiology at Massey University, Palmerston North, New Zealand(Massey University, 2002) Corner, Rene AnneThe two studies included in this thesis are part of a larger research programme evaluating tools to aid in the eradication of bovine tuberculosis (TB) from cattle in New Zealand. The first study was a survey of farmer’s attitudes towards the National Pest Management Strategy (NPMS) and tuberculosis control. The second study validated the population component of PossPOP, a spatial stochastic simulation model of TB in a wild possum population. A postal questionnaire survey identified variation of attitudes of 404 farmers in four regions of varying TB status within New Zealand. Farmers were stratified by region, enterprise type, area TB classification and herd TB status. Of the farmers contacted by telephone prior to sending out the questionnaire 91% agreed to participate in the study and 83% of these farmers returned a completed questionnaire. The questionnaire contained questions on farmer demographics, TB status, herd TB history, farm management practices and attitudes towards the control of TB. Farmers with infected herds were generally positive about the control program and believed that TB could be eradicated from their herds. A number of farmers were concerned about proposed changes to the NPMS, such as the implementation of direct payment of TB testing costs by farmers and removal of compensation for infected cattle. An important finding was that the majority of farmers were not aware that the Animal Health Board was in charge of the NPMS. PossPOP was built using the first 22 months’ data from a longitudinal study of a possum population run at Castlepoint in the lower North Island of New Zealand. Data from the remaining 9 years of the study was used set for model validation. PossPOP was validated by comparing age distribution, sex structure and the proportion of births, deaths and immigrations in the modelled population against the field population. There was general agreement between the model and the field population and also published population patterns. PossPOP produced a stable population over time at different densities, with similar temporal patterns to the field population. Emergent biological properties were examined, such as rate of population rebuilding after a major population cull, the removal of immigration from both populations and age specific mortality. The field population grew much more rapidly following a cull compared with the PossPOP population due to home range expansion of possums that were living on the periphery of the study site, which was not programmed into the model. These results showed that while PossPOP models a small area, it reflects patterns of control over large areas making it a useful tool to evaluate large scale possum control strategies.Item The behavioural response of a small prey animal to the odour cues of familiar predators in a New Zealand model system : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Zoology at Massey University, Manawatu, New Zealand(Massey University, 2012) Carter, Gaylynne MarieThere is a rich ethological literature examining the effects of predators upon the behaviour of their prey. There are also apparent discrepancies in results reported particularly with respect to wild versus domesticated or captive subject species, and especially amongst Rodentia where predator avoidance behaviours predominate. Using New Zealand as a model system, the aims of this thesis were to determine how prey animals respond behaviourally to a familiar predator odour; to evaluate the role of predator exposure in prey behaviour; and to test whether captive-derived results are applicable in wild populations. I undertook experiments under three different conditions: the standard laboratory Y-maze choice test, an enclosure test, and a field test. In each experimental scenario the prey (ship rats) were initially presented with odour treatments derived from a familiar predator (stoat), familiar non-predator (possum) and novel non-predator (chinchilla). The rats’ behaviour was then video recorded for analysis of either avoidance or non-avoidance behaviour. The captive enclosure rats and the free-living rats exhibited clearly definable non-avoidance responses to stoat odour, but in the Y-maze the same captive rats did not exhibit a consistent response. I hypothesized that the non-avoidance behaviours represented a form of predator inspection behaviour. Further captive enclosure and field experiments aimed to test whether the non-avoidance response to stoat odour was specific or generalized. Under both conditions the most marked non-avoidance behaviour was in response to male stoat and secondarily to the mixed sex cat odour. My research concluded with a snap trap experiment pairing stoat-odour lure and no-odour snap traps, yielding an overwhelming capture success in the stoat-odour lured traps. Significant developments in the study of predator-prey behaviour resultant from this research include the development of a captive experimental protocol that generates comparable field results, the description of non-avoidance responses to predator odour, and the reporting of predator inspection a behaviour previously unreported in ship rats and rarely reported within Rodentia. Future studies should aim to verify the non-avoidance behaviours in other rat species as a first step to determining whether this is a ship rat specific behaviour, or if its lack of expression in other rodents is an experimental artefact.Item Leptospirosis in free-living animals in New Zealand, with particular reference to the possum (Trichosurus Vulpecula) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Pathology and Public Health at Massey University(Massey University, 1978) Hathaway, Stephen CliveA serological survey of 600 possums (Trichosurus vulpecula) from farmland environments in the southern half of the North Island of New Zealand revealed that titres against leptospires of the Hebdomadis serogroup were present in 52% of sera. Bacteriological studies identified the causative organism as Leptospira interrogans serovar balcanica. This serovar had previously been isolated only in Eastern Europe; from man, cattle and pigs. Isolation of leptospires from kidneys was aided by the use of a system involving whole kidney homogenisation in γ-sterilised plastic bags in a 'Coleworth Stomacher'. Comparison of cultural and serological results demonstrated that, when titres were read at low minimum serum dilutions, the serological prevalence was an accurate indicator of the bacteriological prevalence. Field surveys and experimental studies demonstrated that the possum was a typical maintenance host for balcanica. Experimental infection was easily established and 50% of animals were still leptospiruric one year after infection. Experimental infection with hardjo could not be established, and it is considered that previous reports of endemic hardjo infection in possums in New Zealand could be incorrect. There was a marked difference in the age-specific prevalence of balcanica infection in possum populations, with infection being restricted to sexually-mature animals. Evidence is presented to support the hypothesis that infection becomes established following behavioural changes associated with the onset of sexual maturity. It is suggested that the transmission of balcanica within a population is dependant on direct contact between animals rather than environmental contamination. No correlation could be shown between the prevalence of infection in different populations and the nature of the habitat. A consistent paradoxical reaction to hardjo was found in sera from possums infected with balcanica. Chromatographic studies revealed that this was due to heterologous agglutinating activity of antibodies of the IgM class. Chromatographic studies also indicated that, following infection, the transition of the predominant agglutinating activity in sera from antibodies of the IgM class to antibodies of the IgG class was considerably slower than in eutherian mammals. Balcanica was found to haemolyse red blood cells of several species. An in vitro haemolysin test for the differentiation of balcanica and hardjo isolates is described. Haemolytic activity has not been previously demonstrated in other members of the Hebdomadis serogroup. Investigations of other small free-living mammals revealed that serogroup Ballum infection was endemic in ship rats (Rattus rattus), house mice (Mus musculus) and hedgehogs (Erinaceus enropaeus) in natural and syanthropic biotopes. The Norway rat (Rattus norvegicus) was also shown to be capable of maintaining a focus of Ballum serogroup infection when the population density was high. No leptospires from other than the Ballum serogroup were isolated from the rodents examined. Field evidence suggested that there was no predator-chain transmission of leptospiral infection from rodents to free-living carnivores. -Birds were similarly found to be unimportant in the epidemiology of leptospirosis in the ecosystems studied. The nidality of leptospirosis was investigatad in an intensive farming environment for a period of two years, and well-defined maintenance-host parasite relationships for different serovars were defined in both domestic and free-living species. No cultural and very little serological evidence of interspecies transfer was found, despite the apparent opportunity for transfer of infection. The concept of a maintenance host for a particular leptospiral serovar was investigated using a laboratory mouse model. As a consequence of this investigation and field studies, the characteristics of a maintenance host for a leptospiral serovar are redefined.Item B lymphocyte activities in the opossum, Trichosurus vulpecula : a thesis presented in partial fulfilment of the requirement for the degree of Doctor of Philosophy at Massey University(Massey University, 1980) Ramadass, PachaikaniThe evolution of vertebrate immunity from the level of the protochordates to that of the metatherians is reviewed. Using standard methods IgG, IgM and IgA were isolated from the serum or intestinal fluid of the Australian brush-tailed opossum, Trichosurus vulpecuia. These were characterized in terms of their molecular weights, amino acid and carbohydrate compositions and values for their concentrations in serum were calculated. Two forms of IgG were seen which differed in their abilities to bind to insoluble matrices and also in their molecular weights. No antigenic differences were seen between them on analysis by agar diffusion . The molecular weight of the IgA seen in intestinal fluid and results from its analysis by agar diffusion suggest that the molecule may lack secretory component. B lymphocytes were identified by their surface immunoglobulin and their complement and Fc receptors. The number of these cells in blood and various lymphoid tissues of T.vulpecula was found to be similar to the values reported for mice and humans. Lymphocyte fractionation on nylon wool columns confirmed that the markers employed were associated with an adherent cell population. Blood lymphocytes were stimulated in vitro with a range of mitogens and the degree of transformation achieved with each was assessed by the cells uptake of tritiated thymidine. Insoluble concanavalin A, pokeweed mitogen and lipopolysaccharide, in that order, were the most effective of the mitogens used on unfractionated blood lymphocytes. These three mitogens were further used in studies in which nylon wool fractionation of blood lymphocytes was used to prepare B cell- and T cell-enriched cultures. Lipopolysaccharide was the only mitogen to stimulate B cells more than T cells. Insoluble concanavalin A consistently stimulated T cells to a greater extent than B cells as did pokeweed mitogen. The ultrastructure of mitogen-stimulated cells was studied by electron microscopy and it was shown that lipopolysaccharide induced the formation of plasmablasts which resembled those of eutherians. Mitogen-stimulated cells were also analysed for their production of immunoglobulins, the levels of de novo synthesised materials being measured by their incorporation of isotope-labelled leucine provided in the culture medium. Both secreted and intracellular proteins were measured in this way. Lipopolysaccharide, pokeweed mitogen and insoluble concanavalin A all induced significantly increased levels of 19S and 7S secreted proteins, these proteins being separated by gel filtration. Pokeweed mitogen induced the synthesis of significantly increased levels of both 19S and 7S intracellular proteins, while lipopolysaccharide and insoluble concanavalin A significantly increased the levels of 19S protein only. The presence of IgM and IgG in the 19S and 7S fractions was shown by their precipitation with class-specific antisera. The immune responses of T.vulpecula to a particulate and a soluble antigen were compared with those of rabbits to the same antigens. Sheep erythrocytes, at two dose levels, were injected intravenously. The responses of opossums to 5x109 erythrocytes were appreciably more rapid than those of the rabbits. The responses of the two species to 25x109 erythrocytes were similar in the titres attained and the time taken to do so. The distribution of haemagglutinating activity between IgM and IgG was studied and found to be essentially the same for both species for both levels of antigen. The responses of opossums to bovine serum albumin injected intramuscularly with Freund's adjuvants were similar to those of rabbits. It is concluded that the B cell-dependent immune functions of T.vulpecula are as efficient as those of other metatherians and compare favourably with those of eutherians.Item Fur growth and replacement in the brushtail possum, Trichosurus vulpecula, Kerr : a thesis submitted in partial fulfilment of requirements for the degree of Doctor of Philosophy in Zoology at Massey University(Massey University, 1989) Nixon, Allan JohnSeasonal hair replacement in the brushtail possum was described using skin histology and fibre measurement. Possums were held in individual cages under conditions of natural light and temperature for an observation period of 26 months, and skin and fibre samples taken from the mid dorso-lateral position at three week intervals. Counts of hair follicles from transverse sections were used to measure hair follicle activity, and changes in compound follicles. Periods of hair growth were poorly synchronized between individuals, and peak levels of follicle activity did not exceed 40 percent. Derived follicles continued to form in mature possums. The number of follicles present in compound follicles increased by an average of 23 percent per annum, amongst six adult animals of various ages. Much of the fibre growth in possum skin was therefore attributable to follicle neogenesis. On average, only 13 percent of fur fibres were replaced per annum. Primary central follicles producing guard hairs undergo normal shedding and replacement cycles. Levels of growth and seasonal variation amongst members of the original wild population were similar to those of captive animals. Using skin pigmentation as an indicator of hair growth (or "moult"), a survey of commercially collected pelts also verified the high individual variation and tendency for spring-summer growth. Also, variation in the proportions of pigmented pelts over time differed between males and females, and pigmentation was greater in juveniles than in adults. A diffuse topographic growth pattern in possums was demonstrated by fur dyeing and skin pigment patterns. However, much fur growth in possums occured in discrete patches which were attributable to repair of fur lost in intraspecific encounters. Growth of this type was most prevalent about the time of breeding in May, when 89 percent of pelts showed moderate or heavy patchy growth. The median duration of pluck induced follicle activity was 82 days, and growth time of guard hairs was 99 days. These times did not vary with differing ambient temperatures. Peak growth rates were 0.63 mm/day for pluck induced, and 0.58 mm/day for spontaneously growing guard hairs. The force required to extract fibres varied from 0.88 g/fibre under anaesthesia to 0.05 g/fibre shortly after death. Findings were discussed in relation to hair growth in eutherian fur bearers, possible control factors, and commercial management of the species.Item Transmission of tuberculosis (Mycobacterium bovis) by possums : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University(Massey University, 1995) Jackson, R.Tuberculosis caused by Mycobacterium bovis was diagnosed in 59 of 632 possums (Trichosurus vulpecula) individually identified over a 52 month period, during a longitudinal study of the naturally occurring disease in possums at a 21 hectare bush pasture location on a farm at Castlepoint in the Wairarapa. The disease exhibited marked spatial and temporal clustering and was continuously present in the population for the whole period. The disease had a relatively long duration of up to 22 months and four distinct stages were demonstrated in cross-sectional studies. Among tuberculous possums, prevalences of up to 0.15 (±0.11) were recorded in the first stage prior to development of gross lesions. After dissemination started, the disease showed rapid generalisation to multiple sites by haematogenous and/or lymphatic spread to the next stage when gross lesions were evident, particularly in lung, axillary and inguinal lymphocentres. In the third stage, lesions were disseminated through almost all lung lobes, discharging fistulae were common and kidney, intestine and mammary gland were commonly affected by both gross and microscopic lesions. Behaviour and outward signs of health were unaffected prior to the terminally-ill stage, lasting for up to 2 months. In common with other marsupials studied to date and in contrast with most eutherians, there are no popliteal lymph nodes and efferent drainage from the inguinal lymphocentre passes directly to the deep axillary group of lymph nodes via an inguinoaxillary trunk. All subcutaneous lymph drainage passes through either the superficial cervical or the axillary lymphocentres before entering the venous system. Studies of survival of Mycobacterium bovis organisms in different natural habitats showed a relatively short period of survival of M. bovis outside hosts and support a conclusion that environmental contamination of pasture, particularly in summer months, may be relatively unimportant in the epidemiology of tuberculosis in cattle, deer and possums. The weight of evidence favours transmission of infection by the respiratory route and it would seem that transmission of tuberculosis between possums occurs through two major and one minor pathway. The first major pathway is pseudo-vertical transmission from mother to joey during the rearing process. The second major transmission mechanism is direct horizontal transmission among adult possums with available evidence suggesting that this takes place around the locality where a possum dens, probably during competition and threat/agonistic behaviour and during courting and mating activity. The third and probably least important pathway is indirect transmission among mature possums. None of three ELISA assays reliably detected possums infected with tuberculosis and poor test performance was exacerbated by inconsistency between results from serially collected samples from known tuberculous possums.