http://hdl.handle.net/2123/929 http://ses.library.usyd.edu.au/retrieve/4736 http://hdl.handle.net/2123/929 Search the Channel search http://ses.library.usyd.edu.au/simple-search http://hdl.handle.net/2123/971 Title: Investigations of adult sheep vaccinated with Gudair® for protection against ovine Johne’s disease.<br/><br/>Authors: Hazelton, Mark<br/><br/>Abstract: This observational study closely examined the gross and histopathological lesions associated with ovine Johne’s disease in sheep vaccinated as adults with Gudair®. Two cohorts of Gudair® vaccinated sheep were used from two separate properties both with high OJD mortality rates (>5%). All sheep had been vaccinated outside the recommended 1 to 4 months of age, mostly as adults. Vaccination injection site lesions were prevalent (>39%) in both cohorts of sheep at least 6 months post vaccination. At necropsy, lymphatic cording was found to be a good indicator of OJD and highly correlated with the formation of a multibacillary lesion. This study indicates the possibility for misdiagnosis of OJD based on gross pathology alone and emphasises the necessity for histological confirmation. Histopathology from the two cohorts of sheep reports a high proportion of multibacillary lesions in one group and a predominance of paucibacillary lesions in the other. This suggest the use of the Gudair vaccine could effect the type of histological lesion developed in OJD infected sheep vaccinated as adults, however further research is necessary to identify additional property factors which could be involved.<br/><br/>Description: This work has been digitally archived on behalf of Meat & Livestock Australia Limited by the Sydney eScholarship Repository at the University of Sydney Library. http://hdl.handle.net/2123/970 Title: Culture of Mycobacterium paratuberculosis from soil<br/><br/>Authors: Hope, Anne<br/><br/>Description: This work has been digitally archived on behalf of Meat & Livestock Australia Limited by the Sydney eScholarship Repository at the University of Sydney Library. http://hdl.handle.net/2123/969 Title: Surveillance and risk assessment of Ovine Johne's disease in Australia<br/><br/>Authors: Sergeant, Evan W<br/><br/>Abstract: Ovine Johne’s disease (OJD) was first diagnosed in Australia in 1980, and by January1998, more than 200 infected flocks had been identified in New South Wales, Victoriaand South Australia. In 1998, in response to the increasing number of infected flocksand industry concerns about the spread of the disease, a 6-year, AUD 40.1 millionnational program commenced, with the aim of controlling the disease while furtherresearch was undertaken to evaluate future control or eradication options. This researchwas undertaken as part of the national OJD program, to improve our understanding ofthe performance of existing and new diagnostic tests for the disease, to estimate diseaseprevalence and distribution and to develop a simple, objective system for assessingflock-risk of infection.In the first study, the sensitivities and specificities of an absorbed enzyme-linkedimmunosorbent assay (ELISA) and an agar-gel immuno-diffusion (AGID) test for thedetection of Johne’s disease in sheep were estimated using data from six known infectedand 12 assumed uninfected sheep flocks. Logistic regression analysis was used to testfor significant effects of lesion score and condition score, with flock included in themodel as a random effect.Estimated specificities were 95% (95% CI: 93.4, 95.6%) and 99% (98.4, 99.4%) forELISA cut-point ratios of 2.4 and 3.6 respectively, and 100% (99.7, 100.0%) for theAGID. Estimated sensitivities were 41.5% (35.0, 48.3%), 21.9% (16.6, 27.9%) and24.6% (19.1, 30.7%) for ELISA cut-point ratios of 2.4 and 3.6 and for AGID,respectively. ELISA and AGID sensitivities varied between flocks and betweencategories of lesion score and condition score. Sensitivity was highest in thin sheep andivin sheep with multibacillary lesions. The effects of lesion type and condition score ontest sensitivity were both significant in the logistic regression analysis for the AGID andELISA at both cut-points and the flock effect was significant for the AGID but not forthe ELISA at either cut-point.In the second study, the flock-level sensitivity of pooled faecal culture and serologicaltesting using AGID were compared in 296 flocks in New South Wales during 1998. Theoverall flock-sensitivity of pooled faecal culture was 92% (82.4%, 97.4%) compared to61% (50.5%, 70.9%) for serology (assuming that both tests were 100% specific). Inlow-prevalence flocks (estimated prevalence <2%), the flock-sensitivities of pooledfaecal culture and serology were 82% (57%, 96%) and 33% (19%, 49%) respectively,compared to 96% (85%, 99.5%) and 85% (72%, 93%) respectively in higher-prevalenceflocks (estimated prevalence ≥2%).In a third study, the results of abattoir surveillance for OJD carried out during 2000were analysed to estimate the prevalence of infected flocks in three regions of NewSouth Wales and in other States. A Bayesian approach was used to adjust apparentprevalence estimates for the assumed flock-sensitivity and flock-specificity of abattoirsurveillance, and to allow for uncertainty about the true values of these measures. The95% probability limits for flock-prevalence at 31 December 2000 were 0.04% – 1.5%,8% – 15% and 29% – 39% for low, moderate and high prevalence regions of NewSouth Wales respectively. The other States generally had an upper 97.5% probabilitylimit of about 1% or less. Based on this analysis, there were probably between 2,000and 3,700 infected flocks in Australia at 31 December 2000, with more than 80% ofthese in a relatively small geographic area of central and southern New South Wales.vThe final part of the current research was to develop a simple quantitative model forflock-risk of OJD, based on estimated flock-prevalence and within-flock prevalence fordifferent classes of flocks, depending on their location and status. A method is alsodescribed for modifying this risk-score for individual flocks, according to the presenceand level of individual flock risk factors such as the use of vaccination, testing historyand the presence and number of infected neighbours. This flock-based approach to riskassessment could be supported by varying degrees of regulatory control over sheepmovements, or could be adapted to a deregulated environment, with sheep producerstaking responsibility for their own risk management, rather than the State or Territoryregulatory authorities.<br/><br/>Description: This work has been digitally archived on behalf of Meat & Livestock Australia Limited by the Sydney eScholarship Repository at the University of Sydney Library. http://hdl.handle.net/2123/968 Title: DNA typing of Johne's disease organisms.<br/><br/>Authors: Whittington, R. J<br/><br/>Description: This work has been digitally archived on behalf of Meat & Livestock Australia Limited by the Sydney eScholarship Repository at the University of Sydney Library.