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    A study of tuberculosis in hedgehogs so as to predict the location of tuberculous possums : a thesis submitted in partial fulfilment of the requirements for the degree of Masters of Veterinary Studies at Massey University, Palmerston North, New Zealand
    (Massey University, 1998) Gorton, Robyn Jane
    Hedgehogs are spillover hosts for Mycobacterium bovis, which means the prevalence of disease in the hedgehog is directly related to the prevalence of disease in a local reservoir population such as the possum. Possums have home ranges similar to that of hedgehogs and on large farms, locating a tuberculous hedgehog coud substantially reduce the area where extensive control is required to eliminate tuberculosis from the wild animal population. Male animals usually have a larger home range than females and this is true of the hedgehog. In utilising the knowledge of a hedgehog’s home range, female hedgehogs could provide a specific local indicator of the presence of tuberculous possums and male hedgehogs could locate the general region on the farm with tuberculous possums. The hedgehog could also be considered a temporal indicator of tuberculosis in the wild animal population especially where there has been a history of tuberculosis. The longevity of the hedgehog is reasonably short (2-3 years in the wild) and should sufficient control of other tuberculous animals occur then the disease will also disappear from the hedgehog population. Hedgehogs from this study were noted to be carriers of Salmonella enteriditis, Sarcoptes scabiei. This is believed to be the first report of these pathogens associated with hedgehogs in New Zealand.
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    Risk factors for detection of recurrent bovine tuberculosis in New Zealand cattle and deer herds 2005-2011 : a dissertation presented in partial fulfillment of the requirements for the degree of Master of Veterinary Studies (Epidemiology) at Massey University, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand
    (Massey University, 2014) Dawson, Kara Lee
    In New Zealand, under the national bTB eradication strategy, bovine tuberculosis (bTB) has had a sustained decrease in prevalence since its peak in 1994 at 1700 infected herds. With the success of control measures, recurrence of infection in cattle and deer herds that have previously tested to a clear status is a problem that has recently become more apparent. Uncontrolled movement of cattle and deer from these herds pose a risk to the bTB eradication strategy. A retrospective cohort study was conducted to identify herd-level risk factors for bTB recurrence. Data were collected from 356 New Zealand cattle and deer herds that met the following criteria: (1) a culture positive case of bTB had been identified on or after 1 June 2006 (the index bTB episode), (2) the herd status had been cleared by testing that was completed by 1 November 2010, and (3) the clear status was not achieved by destocking. The outcome of interest for this study was defined as detection of a subsequent bTB episode before the end date of the study, 5 May 2011, by routine tuberculin testing or by slaughter surveillance. Herds were censored if no further bTB episode occurred by 5 May 2011. A Cox proportional hazards model was developed to quantify the magnitude of a series of herd-level risk factors on the daily hazard of bTB recurrence. Disease control area was included in the model as a fixed effect to account for confounding. There was a positive relationship between the daily hazard of recurrence and: (a) the number of bTB episodes in a herd prior to the first episode (HR [hazard ratio] 3.2 for two prior episodes, 95 % CI 1.2-8.5; HR 86.7 for five prior episodes, 95 % CI 13.8-580), (b) the presence of more than one bTB positive animal at the index bTB episode (HR 2.3: 95 % CI 1.2-4.3) and (c) the presence of one or more cleared test-positives at the final clearance test at the index episode. The proportional hazards assumption was violated for the latter variable so a time dependent covariate was introduced into the model to account for the variable effect of the presence of cleared test-positives at the final clearance test over time. The monthly hazard of recurrence during the first two years after clearance was significantly increased in herds with one or more test-positive animals at the final test (HR 2.8: 95 % CI 1.2-6.4), but this association was no longer significant more than two years after clearance (HR 1.5: 95 % CI 0.6-3.6). We conclude that the presence of unresolved infection in a herd is a contributor to further bTB episodes in the first two years after clearance. TBfree New Zealand is reviewing policies to increase the sensitivity of detecting residual infection before clearance and to intensify post clearance testing and movement tracking in herds with risk factors.
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    Epidemiological analysis of tuberculosis in cattle herds : a thesis submiited in partial fulfilment of the requirements for the degree of Master of Philosophy, Massey University
    (Massey University, 1997) Zewdie, Sileshi
    Studies were made of the occurrence and distribution of bovine tuberculosis in the Taumarunui and Masterton veterinary districts, within which endemic wildlife tuberculosis is widespread. These districts were compared with the movement control herds of the surveillance areas of New Zealand, which are free of wildlife tuberculosis. The study covers the period from 1985-1990. The frequencies of tuberculosis infection for different categories of herds and different veterinary districts were examined and comparisons made of rates and risk of disease between the herd categories and districts under consideration. A comparison of incidence measures showed a strong positive correlation between cumulative, corrected and true incidence values. Cumulative and corrected cumulative incidence values calculated for calendar, financial and test years were compared. Some disparity was found between annual cumulative incidences and annual corrected cumulative incidences calculated on the basis of calendar and test years, with measures calculated on the basis of test year having the highest values. Regional comparisons showed that movement control herds in surveillance areas had higher incidences of tuberculosis than did herds in the Taumarunui and Masterton veterinary districts. Beef dry stock herds had higher incidences of tuberculosis than did dairy or beef breeding enterprises. Endemic areas had the highest incidence of all tuberculosis area classes. Simple regression analyses indicated that the risk of tuberculosis for any animal in a herd was more closely related to the level of infection in adult cows than any other age or sex group. Cumulative incidence in yearlings was a poor predictor of risk for individual animals in a herd but there was a stronger relationship for the level of infection in 2 year-old animals. Stepwise logistic regression was used to explore and quantify associations between cumulative incidence and putative risk factors. The odds of cattle testing positive in herds in endemic areas was about five times as high as in herds in surveillance and fringe areas, where the risks of tuberculosis were about the same. The likelihood of reacting to the tuberculin test was considerably lower for animals in the Masterton and Taumarunui districts than for animals from movement control herds in surveillance areas outside those districts. The overall risk of infection increased slightly from 1985 to 1990. Poisson regression was used to examine the relationships between incidence density and the same independent variables which were examined using logistic regression. The relative risks for infection were higher in beef breeding, beef dry stock and other herd types than in dairy herds. Herds in endemic areas had rates of infection about seven times those in Fringe and Surveillance area herds, where the rates were about the same. The incidence of infection in herds increased with increased herd size and was considerably less in the Masterton and Taumarunui districts than in movement control herds in the Surveillance areas. There was a good general agreement between the logistic and poisson regression models in the overall relationships between the predictor variables common to both models and their respective dependent variables. Survival analysis showed that after going on to movement control for the first time, about 75% of herds could be expected to be still on movement control after 12 months and about 50% after 2 years. Herds in the Masterton veterinary district tended to stay on movement control longer than herds in the Taumarunui veterinary district and Surveillance areas (Risk ratio = 0.69). After 2 years of testing, about 60% of infected herds in the Taumarunui veterinary district and Surveillance areas had come off movement control, compared to 40% of infected herds in the Masterton veterinary district. The survivorship probability of infected herds in Fringe, Surveillance and non-endemic zones for coming off movement control was lower than that for infected herds in endemic zones (Risk ratio = 0.61). The estimated median time on movement control was 3 years for herds from endemic areas and 2 years for herds in Fringe, Surveillance and non-endemic zones. The risk of coming off movement control decreased with increasing herd size. Herds with high levels of cumulative incidence were more likely to stay on movement control for longer periods than those with lower levels of incidence. Simple linear regression indicated that distance from the nearest case herd with tuberculosis, distance from the Rangitoto buffer, distance from the nearest case in year one after breakdown and total number of cattle purchased were poor predictors of cumulative incidence. A multivariate logistic regression analysis of the association between cumulative incidence and putative risk factors during the first year after a breakdown indicated that risk was lower on farms where the main activity was dairying (MAINOP) and in herds in which the proportion of adult cattle (ADULTCAT) was high. Over the whole period for which herds were under movement control, risk levels remained lower for dairy farms and increased as the proportion of beef cattle was increased. Increased rates of infection were associated with the practice of buying replacements (BUYREPLA) in the first year after breakdown and rates were higher for the whole period in herds which ran cattle on agistment (OTHERCAT). Rates were lower on farms where cattle had access to bush (BUSHACCE), but despite the higher rates, survival analysis clearly showed that herds with access to bush could be expected to stay on movement control for longer periods than farms with no bush access. The median time on movement control was 1 year for farms without access to the bush and slightly more than 2 years for farms with access to the bush. Movement control farms without bush access were free from infection by 3 years, whereas farms with bush access took more than 5 years. Both the risk and incidence of infection tended to be lower at higher stocking rates in the short and long term after first going onto movement control. The association between personal qualities of farmers and the risk and rate of infection were also examined using multivariable regression analyses.
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    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 Maynard
    Behavioural 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.
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    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, Solis
    The 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.
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    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 Anne
    The 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.
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    Bovine tuberculosis in brushtail possums (Trichosurus vulpecula) : studies on vaccination, experimental infection, and disease transmission : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University
    (Massey University, 2001) Corner, L A L
    The objectives of the research program were to obtain a better understanding of BCG as a tuberculosis vaccine in possums, and assess its potential as a tool for controlling tuberculosis in wild possum populations. A series of vaccination and challenge experiments were conducted, as well as studies on alternative experimental infection procedures. The program included two field studies, one on the epidemiology of tuberculosis in a population of possums regenerating after localised possum eradication, and the other examined the efficacy of BCG vaccine in a wild population in which tuberculosis was endemic. The first experiments confirmed the earlier published findings that BCG delivered as an intranasal aerosol induced a protective response. The protective response was found to be present 12 months after vaccination and therefore of sufficient longevity to make vaccination a practical control tool. A second study demonstrated that revaccination of possums enhanced protection and a third showed that conjunctival vaccination was as effective as intranasal aerosol. These findings supported the development of a possum activated self-vaccinator that would deliver vaccine as an aerosol. In delivering the spray to both the external nares and the eyes a simple and cheap device could be designed to efficiently vaccinate wild possums. The intratracheal experimental infection procedure used in the vaccination and challenge experiments was not entirely suitable for our purposes. Although it provided an assured level of exposure and repeatable results, all infected possums developed fulminant, rapidly progressive disease, irrespective of the vaccination regime used. Two alternative methods of challenge were examined; the conjunctival route of infection, and natural transmission between experimentally infected possums and susceptible in-contact possums. Conjunctival infection was shown to be a reliable procedure for infecting possums, with the disease that resulted from infection having many of the cardinal features of natural tuberculosis in wild possums. Infection following conjunctival inoculation progressed slowly and may be suitable for studying pseudo-vertical transmission and the efficacy of post-infection vaccination. In studies with captive possums there was little or no transmission of infection between experimentally infected possums and susceptible in-contact possums in the same pen when the experimentally infected animals were selected at random. However, when possums with high levels of social interaction were experimentally infected there was a significant increase in transmission rates. In addition, the possums that became infected by transmission were more socially active than those that remained free of infection. Two aspects of the pathogenesis of tuberculosis in possums were clarified during the experimental infection and natural transmission studies. The duration of preclinical infection, impossible to determine accurately in longitudinal studies on wild possums, was found to range from 6 - 20 weeks. Secondly, the pre-eminence of the aerosol route in naturally transmitted tuberculosis was confirmed. After eradication of possums from a 36 ha site, tuberculosis reappeared within four months. Re-emergence of infection on the site was due to immigration of infected possums, not to the survival of M. bovis in the environment. Each of the four restriction endonuclease analysis (REA) types of M. bovis that caused disease in the possum population showed a different temporal and spatial pattern. BCG vaccine had high efficacy in a wild possum population. Over 2 years, 300 possums were recruited to a study of BCG vaccination. Approximately 50% of the possums were vaccinated, where each possum was vaccinated using both intranasal aerosol and conjunctival instillation. There were significantly more cases of tuberculosis in unvaccinated possums than in vaccinates, with a relative risk of tuberculosis in unvaccinated possums of 3.21. The vaccine efficacy was 69%. The most important question relating to BCG vaccine that remains to be addressed is the ability of vaccination to control tuberculosis in possum populations. This research has demonstrated that BCG vaccine provided protection against M.bovis infection in both captive and wild possums. Future research should be directed towards developing delivery systems for vaccinating wild possums and strategies for vaccine use in wild tuberculous possum populations.
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    Factors associated with the transmission dynamics of bovine tuberculosis in New Zealand : a dissertation presented in partial fullfilment [sic] of the requirements for the degree of Doctor of Philosophy at Massey University, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, Turitea, New Zealand
    (Massey University, 2008) Porphyre, Thibaud Francois Christophe
    This thesis presents the results of a series of studies on the epidemiology of TB in brushtail possum and domestic cattle populations in New Zealand. The first set of studies provides an analysis of the results of routine TB testing carried out in the Featherston area from July 1980 to June 2004. The median annual incidence rate of TB reduced from 4.7 cases per 1000 cattle-years at risk for the period 1986 to 1991 to 1.8 cases per 1000 cattle-years at risk for the period 1992 to 2003, coincident with the use of poisoning to control possums in the surrounding forest park (a major possum habitat area). We identified clusters of cattle TB cases adjacent to the forest park and found no evidence of spatio-temporal interaction of TB risk among farms. Our findings support the hypothesis that possums living in the forest park are a source of bovine TB in this area and that farm-to-farm transmission was not an important mechanism of infection spread. A mixed-effects Poisson regression model was developed to investigate the influence of farm-level covariates on the number of cattle confirmed with TB. The model showed that, despite intensification of possum control activities, proximity to forest parks remained a significant predictor of the number of confirmed TB cases per farm per year. Our analyses identified a significant, 3-fold increase in TB risk in dairy cattle relative to beef conditional on the size of local possum habitat, and confirmed the positive influence of cattle population size and the presence of previous infection status as a determinant of the number of confirmed TB cases per farm per year. The second set of studies investigates details of capture events recorded during a longitudinal, capturemark- recapture study of possums in a 22-hectare study site near Castlepoint, from April 1989 to August 1994. Social network analyses were used to identify contact patterns and to estimate the influence of contact on R0 for bovine TB. The average number of contacts per possum ranged from 20 to 26 per year. We estimated that TB would spread if an average of between 1.94 and 1.97 infective contacts occured per year per infected possum. We evaluated the effect of sex, habitat and contact behaviour of 26 postmortem confirmed TB cases in possums with those of 104 matched controls. Unit increases in the number of infected contacts increased the odds of TB infection by 2.61 (95% CI 1.29 – 5.29, P <0.01). Our results show that individual contact behaviour is a determinant of the presence of TB foci within this population and challenge the hypothesis that contact with many individuals increases the probability of infection. A model to predict spatial variation in possum abundance was developed using a Geographic Information System. Details of possum capture events were obtained from 157 10-trap lines distributed within 42 randomly located transects at Molesworth Station. Two GIS-based models were developed to predict the number of possums caught per line using Poisson regression techniques. The first model used remotely sensed environmental data; the second used a combination of remotely sensed and fine-scale data. Both models provided adequate predictive ability with Pearson correlation coefficients greater than 60%. We conclude that the prediction maps produced from this model provide a useful decision support tool for possum control managers. These results have implications for the management of TB in this area of New Zealand, providing the information that will allow effective control activities to be applied at significantly lower cost.