http://hdl.handle.net/2123/929 2013-05-23T23:47:35Z http://hdl.handle.net/2123/971 Title: Investigations of adult sheep vaccinated with Gudair® for protection against ovine Johne’s disease. Authors: Hazelton, Mark 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. 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. 2003-10-01T00:00:00Z http://hdl.handle.net/2123/970 Title: Culture of Mycobacterium paratuberculosis from soil Authors: Hope, Anne 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. 1997-01-01T00:00:00Z http://hdl.handle.net/2123/969 Title: Surveillance and risk assessment of Ovine Johne's disease in Australia Authors: Sergeant, Evan W Abstract: Ovine Johne’s disease (OJD) was first diagnosed in Australia in 1980, and by January 1998, more than 200 infected flocks had been identified in New South Wales, Victoria and South Australia. In 1998, in response to the increasing number of infected flocks and industry concerns about the spread of the disease, a 6-year, AUD 40.1 million national program commenced, with the aim of controlling the disease while further research was undertaken to evaluate future control or eradication options. This research was undertaken as part of the national OJD program, to improve our understanding of the performance of existing and new diagnostic tests for the disease, to estimate disease prevalence and distribution and to develop a simple, objective system for assessing flock-risk of infection. In the first study, the sensitivities and specificities of an absorbed enzyme-linked immunosorbent assay (ELISA) and an agar-gel immuno-diffusion (AGID) test for the detection of Johne’s disease in sheep were estimated using data from six known infected and 12 assumed uninfected sheep flocks. Logistic regression analysis was used to test for significant effects of lesion score and condition score, with flock included in the model as a random effect. Estimated specificities were 95% (95% CI: 93.4, 95.6%) and 99% (98.4, 99.4%) for ELISA cut-point ratios of 2.4 and 3.6 respectively, and 100% (99.7, 100.0%) for the AGID. Estimated sensitivities were 41.5% (35.0, 48.3%), 21.9% (16.6, 27.9%) and 24.6% (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 between categories of lesion score and condition score. Sensitivity was highest in thin sheep and iv in sheep with multibacillary lesions. The effects of lesion type and condition score on test sensitivity were both significant in the logistic regression analysis for the AGID and ELISA at both cut-points and the flock effect was significant for the AGID but not for the ELISA at either cut-point. In the second study, the flock-level sensitivity of pooled faecal culture and serological testing using AGID were compared in 296 flocks in New South Wales during 1998. The overall flock-sensitivity of pooled faecal culture was 92% (82.4%, 97.4%) compared to 61% (50.5%, 70.9%) for serology (assuming that both tests were 100% specific). In low-prevalence flocks (estimated prevalence <2%), the flock-sensitivities of pooled faecal 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-prevalence flocks (estimated prevalence ≥2%). In a third study, the results of abattoir surveillance for OJD carried out during 2000 were analysed to estimate the prevalence of infected flocks in three regions of New South Wales and in other States. A Bayesian approach was used to adjust apparent prevalence estimates for the assumed flock-sensitivity and flock-specificity of abattoir surveillance, and to allow for uncertainty about the true values of these measures. The 95% 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 New South Wales respectively. The other States generally had an upper 97.5% probability limit of about 1% or less. Based on this analysis, there were probably between 2,000 and 3,700 infected flocks in Australia at 31 December 2000, with more than 80% of these in a relatively small geographic area of central and southern New South Wales. v The final part of the current research was to develop a simple quantitative model for flock-risk of OJD, based on estimated flock-prevalence and within-flock prevalence for different classes of flocks, depending on their location and status. A method is also described for modifying this risk-score for individual flocks, according to the presence and level of individual flock risk factors such as the use of vaccination, testing history and the presence and number of infected neighbours. This flock-based approach to risk assessment could be supported by varying degrees of regulatory control over sheep movements, or could be adapted to a deregulated environment, with sheep producers taking responsibility for their own risk management, rather than the State or Territory regulatory authorities. 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. 2003-08-31T00:00:00Z http://hdl.handle.net/2123/968 Title: DNA typing of Johne's disease organisms. Authors: Whittington, R. J 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. 1998-12-31T00:00:00Z http://hdl.handle.net/2123/966 Title: Survey of potential wildlife reservoirs for Mycobacterium paratuberculosis : final report prepared for MLA by NSW Department of Natural Resources and Environment. Authors: NSW Department of Natural Resources and Environment Abstract: In any disease control program eradication of disease depends upon the protection of disease free animals from potential sources of infection. Sylvatic hosts have the potential to thwart eradication campaigns. An assessment of the risk posed to Johne's disease control by wildlife was conducted in two surveys, one an examination of rabbits in Victoria and another of eastern grey kangaroos. The results from the Victorian survey indicate a lack of any evidence of Johne's disease in rabbits and suggests that, under the conditions examined, rabbits are unlikely reservoir hosts for Johne's disease (although it is impossible to rule out the presence of a "hotspot" of JD in rabbits as exists in Scotland). Similarly, no eastern grey kangaroos were found infected with JD in this survey and while infection cannot be ruled out, it is unlikely to be at significant levels, and eastern greys are unlikely to act as significant reservoirs of Johne's disease infection. 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. 2002-03-01T00:00:00Z http://hdl.handle.net/2123/965 Title: Aspects of the pathogenesis of ovine Johne's Disease. Ph.D. thesis--Faculty of Veterinary Science, University of Sydney, 2003 Authors: Reddacliff, Leslie Anne Abstract: John'es disease is a chronic enteropathy of ruminants cause by infection with M. a. paratuberculosis. This study deals with the enumeration of Australian ovine isolates of M. a. paratuberculosis which will help facilitate research into the pathogenesis and epidemiology of OJD. It also covers the early detection of infection in lambs exposed to Australian ovine strains of M. a. paratuberculosis. Examination of sheep at this early stage, in particular the use of culture from tissues, allowed assessment of the current diagnostic techniques for detection of early infection in sheep and some investigation of early immune responses. The final chapter examines possible associations with host susceptibility to Johne's disease with polymorphisms in a number of genes associated with immune function. 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. 2002-03-01T00:00:00Z http://hdl.handle.net/2123/964 Title: MLA OJD Harvest Year Conference December 8-9, 2005. Abstract: Papers from the MLA 2005 Harvest Year conference program, including research on national and international perspectives of OJD; diagnosis; vaccination; public health and national programs; epidemiology; and economics. 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. 2005-12-01T00:00:00Z http://hdl.handle.net/2123/963 Title: Ovine Johne's Disease : an update of Australian research. Abstract: The Ovine Johne’s Disease (OJD) “Harvest Year” Workshop was held on the 25th March, 2004 at Rydges, North Sydney. The workshop was hosted by Meat and Livestock Australia (MLA) and was attended by researchers, advisors, veterinarians and sheep producers from around the country and provided results and outcomes from the extensive research program, which has been conducted in Australia over the last 5 to 8 years. 14 OJD-related research projects were presented, including research in the areas of vaccination, grazing management, eradication, economics, diagnosis and crossspecies transfer. Following the presentations small group workshops were held to identify the key benefits and potential implications of each study for producers, farm advisors and regional authorities. Potential areas of future research were also identified. 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. 2004-03-01T00:00:00Z http://hdl.handle.net/2123/962 Title: OJD research update and control workshop. University of Sydney Veterinary Science Conference Centre, 24-25 September, 2001. Abstract: A forum aiming to provide the most recent results ot the research conducted under the National Ovine Johne's Disease Control and Evaluation Program, as well as an opportunity for key personnel involved in the management of the disease to develop generic control stategies that may be applicable for particular production systems. The forum also aimed to concentrate on technical issues on how to control the disease on a farm and by extension over a number of farms in districts and regions. 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. 2001-09-01T00:00:00Z http://hdl.handle.net/2123/961 Title: Exposure factors leading to establishment of OJD infection and clinical disease : epidemiology of OJD-1. Authors: Abbott, K. A; Whittington, R. J; McGregor, H Abstract: This study was conducted in order to provide answers for owners of OJD-infected sheep flocks who wish to minimise the economic and biological impact of the disease on their sheep enterprises. The study has demonstrated that careful management of young sheep can reduce the level of OJD in the flock and reduce the death rate. One key finding is that steps taken to limit the degree of exposure of pre-weaned lambs to infection from pastures will lead to reduced rates of severe infection in those sheep in later years. A second key finding is that continuous exposure to OJD bacteria throughout early life results in higher infection rates than exposure which is limited to either the pre-weaning or the post-weaning period alone. A critical factor in management is to provide ‘low risk’ pastures to young sheep at weaning to give them a break from exposure to infection which occurs in the lambing paddocks. We also found that weaned lambs and adult ewes remain susceptible to infection and that there is little evidence for an age-related resistance to OJD. 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. 2004-12-01T00:00:00Z http://hdl.handle.net/2123/960 Title: Development of computer models to describe the epidemiology of Johne's disease in sheep. Authors: AusVet Animal Health Services Pty Ltd; Sergeant, E. S. G Abstract: The pathogenesis, epidemiology and options for control of Johne's disease in sheep were reviewed and mathematical models developed to simulate the spread of Johne’s disease within infected flocks, and between flocks on a regional basis. The models (the OJD Flock Model and the OJD Regional Model) also allow the evaluation and comparison of various control options at both flock and regional levels. Adequate data is still unavailable to allow accurate estimates of the true values for many of the models' parameters. However, as more precise estimates of the values of key parameters become available, the models will allow a rapid assessment of the likely impact of these values on our understanding of the disease. 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. 2002-06-01T00:00:00Z http://hdl.handle.net/2123/959 Title: Ovine Johne's Disease : an update of Australian and international research. Abstract: A summary of the national and international research being conducted into OJD from a one-day research forum held at the University of Sydney, July 2002. The report contains reviews of the 7th International Colloquium on Paratuberculosis held in Bilbao, Spain (June, 2002), progress reports on Australian research projects, executive summaries from key completed OJD research projects, details on new research projects under consideration and results from the brainstorming session on future reserach directions. 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. 2002-07-01T00:00:00Z http://hdl.handle.net/2123/958 Title: Longitudinal study of OJD and the effects of whole flock vaccination with Gudair : whole flock OJD vaccination at Merrill. Authors: Windsor, Peter Abstract: Ovine paratuberculosis or Johne’s disease is an insidious mycobacterial infection of sheep capable of causing wasting and death. It has emerged in recent years in Australia as a cause of significant losses in some infected sheep flocks. MLA Project OJD.015 was commenced to enable a detailed longitudinal case study of an attempt to control the disease in a large self-replacing Merino flock at Gunning in NSW with an owner-estimated annual mortality rate up to 25%. Vaccination of the whole flock with exception of a small group in each age cohort was conducted, with documentation of the effects of vaccination and other strategies on mortalities and mycobacterial faecal excretion rates and mortalities in all age groups of animals. The study concluded that the significant decline in mortality risk from 24.2% to 2.85 during the study may only be partially attributed to the increased flock immunity following vaccination. By accompanying vaccination with extensive changes in flock management, including culling of clinical cases, sale of ‘at risk’ stock and introducing of replacements and reduction in stocking rates, control of the losses can be rapidly achieved in an infected flock with a high prevalence of OJD. This project has enhanced the knowledge and understanding of the performance of this vaccine under Australian conditions in a high OJD prevalence environment and recommends that field evaluation of the performance of the vaccine continue, particularly in low challenge environments. 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. 2005-03-01T00:00:00Z http://hdl.handle.net/2123/957 Title: Pilot study : tracer weaner trial for ovine Johne's Disease : National Ovine Johne’s Disease Control and Evaluation Program. Authors: NSW Agriculture. Elizabeth Macarthur Agricultural Institute Abstract: Eradication of ovine Johne’s disease requires destocking sheep and spelling land until Mycobacterium avium subsp. paratuberculoisis has died out. There is no simple way to assess the residual level of contamination or the risk this poses to livestock. Consequently small groups of Merino weaners were orally dosed with M. avium subsp. paratuberculosis. Within 7-14 weeks the organism could be cultured from various locations in the gastrointestinal tract and associated lymph nodes. In addition, the results of a skin test were positive in 66% of weaners in which the organism had established an infection and were negative in uninfected sheep. The results of tests for gamma interferon were positive in some infected weaners but also in some of the controls. An ELISA test was not useful at this early stage of infection. Overall, the results suggest that weaner sheep could be used as sentinels in an infected environment, but this requires validation in a controlled field trial. Furthermore, the results suggest that the infectious dose of M. avium subsp. paratuberculosis may be higher than previously thought. 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. 2000-06-01T00:00:00Z http://hdl.handle.net/2123/956 Title: Development of a rapid cost effective test for ovine Johne's Disease based on testing of pooled faeces : final report. Authors: Marsh, Ian; Whittington, Richard Abstract: This project was undertaken to develop and evaluate a rapid, cost-effective, flock test for Mycobacterium paratuberculosis in pooled faecal samples, based on hybridisation-capture polymerase chain reaction (HC-PCR). However, a simpler direct technique (DPCR) was found to be more sensitive than HC-PCR. About 67% of culture positive pooled faecal samples were positive when tested using DPCR. In a blind trial, 83% of 12 farms identified by culture of pooled faecal samples were detected using DPCR. The cost of DPCR is no greater than that of other flock detection strategies. The test is suitable for use in the National Ovine Johne’s Disease Control and Evaluation Program. A constraint exists in that Veterinary Committee does not recognise the results of DNA-based tests for M. paratuberculosis as being definitive. The costs of follow-up testing to confirm infection are high. Recommendations are made to improve the test and reduce its cost. 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. 2000-06-30T00:00:00Z http://hdl.handle.net/2123/955 Title: Survival of Mycobacterium paratuberculosis in the environment. Authors: Schroen, Chris; McDonald, Wendy; Butler, Kym; Condron, Robin; Hope, Anne Abstract: Reducing the survival of Mycobacterium paratuberculosis (Mptb)outside the host animal has long been attributed to environmental factors such as elevated temperature, pH, ultraviolet light and dryness although without direct scientific evidence of the contribution of these factors. The experiment reported here evauluates these four factors - ultraviolet radiation, soil tepmperature, pH, moisture plus organic matter - for their effect on the survival of Mptb from soil as measured by proportional recovery using the Whitlock double incubation and BACTEC culture method. In this study, soil moisture and soil temperature were the most significant environmental factors affecting the survival or death of Mptb. Ultraviolet radiation appeared to have no effect and different soil types and variable sensitivity of culture obscured the effect of pH. 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. 2000-08-01T00:00:00Z http://hdl.handle.net/2123/954 Title: Prevalence of Johne's disease in rabbits and kangaroos Authors: Abbott, K. A Abstract: This report presents the results of a study of 300 rabbits and 300 kangaroos on 10 farms in NSW on which JD is endemic in the sheep flock. No evidence of active infection of kangaroos or rabbits was found despite evidence in one case that the causative bacterium was present in the faeces of a kangaroo from a farm on which the sheep flock was known to be heavily infected. The estimated prevalence of JD infection in kangaroos and rabbits on OJD-infected farms in NSW is 0%, with an upper 95% confidence limit of 1%. While this study does not allow us to conclude that infected wildlife will never be a significant reservoir of infection in cases where absolute freedom from disease is required, such as in eradication programs, it does show that kangaroos and rabbits pose an insignificant risk as a source of re-infection with OJD on farms which are undertaking strategies to reduce infection. 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. 2002-02-01T00:00:00Z http://hdl.handle.net/2123/953 Title: Identification of risk factors for OJD infection-level in sheep flocks. Authors: Toribio, Jenny-Ann; Dhand, Navneet; Whittington, Richard Abstract: The level of clinical disease experienced due to ovine Johne’s disease (OJD) appears to vary considerably between infected sheep flocks in Australia, even for flocks in the same locality that appear to have similar characteristics. This has led to speculation on the cause. Risk factors for the severity of OJD were identified in this project. They were related to some farming practices such as fertiliser application, as well as to flock management and soil type. In particular weaner management and nutrition of sheep to hogget stage were important factors that producers can optimise to reduce the impact of OJD. High soil fertility, organic matter and clay content were also important factors associated with higher levels of OJD. There was less OJD associated with sandy soils. Further research is required in order to determine how these soil characteristics affect the prevalence of OJD and how best to manage soil and pasture to mitigate the losses due to OJD. 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. 2005-06-30T00:00:00Z http://hdl.handle.net/2123/952 Title: Preliminary study on the potential cost at slaughter of OJD vaccination site lesions to the Australian sheep industry. Authors: Eppleston, Jeff Abstract: This report presents the results of a pilot project to predict the risk of discounts being applied in Australia due to OJD vaccination site lesions as vaccine use expands. This includes a review of discounting in New Zealand as well as a preliminary survey of the prevalence of lesions and actual discounts applied to slaughtered vaccinates in Australia. Information from New Zealand suggests that the greatest discounts are applied to trimmed high value lamb carcases that are destined for export in whole carcase form as a result of downgrading to a lower quality grade. In Australia the greatest risk of discounting is likely to be in purebred merino lambs sold into the prime lamb market, but the low proportion exported as carcases would limit the discount applied. The prevalence of lesions observed was 18% for mutton and 65% for lamb carcases. The value of the trim removed was insignificant, the labour cost of its removal was nil and no carcase was downgraded to a lower value grade. However this study was conducted at a time of low sheep supply in carcases vaccinated at the recommended site and caution should be exercised in extrapolating these results to oversupplied market situations or in sheep vaccinated at alternate sites. 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. 2004-10-01T00:00:00Z http://hdl.handle.net/2123/951 Title: Determination of individual animal-level sensitivity of abattoir surveillance for ovine Johne's Disease. Authors: Bradley, Tracey Abstract: This project aimed to estimate the sensitivity of abattoir surveillance for ovine Johne’s disease (OJD) at an individual animal level. Currently abattoir surveillance for OJD occurs in 21 meatworks around Australia and since late 1999 over 16 million sheep have been examined by this method. Abattoir inspection is an extremely efficient and economical method of regional surveillance for OJD but could also be used for negative assurance purposes if the sensitivity were known. The trial involved three inspectors working in different OJD prevalence areas and compared their diagnoses with the gold standard of histopathology for approximately 1200 sheep from known infected properties. The sensitivity level for the best inspector was 87.3%. A “dummy run” of presumed negative sheep yielded a very low false positive rate. This trial has established that for the lines of sheep examined, an average sensitivity of 70% is applicable. However for the purposes of a flock negative assurance system in a low prevalence flock, a sensitivity level of 50% would be more appropriate. This potential use of this methodology for flock assurance purposes relies on an accurate identification system for sheep. 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. 2002-09-01T00:00:00Z http://hdl.handle.net/2123/950 Title: Epidemiology of ovine Johne's disease 2 - pasture contamination level and age susceptibility. Authors: Whittington, Richard; McGregor, Helen Abstract: To develop pasture management strategies for control of ovine Johne’s disease, research was conducted in a flock of 840 sheep to determine whether age of sheep and pasture contamination levels affect ovine Johne’s disease. Lambs (median age 5.5 months at the start of the trial) were highly susceptible to infection and should not be exposed to high levels of contamination or a proportion will develop severe infection leading to death. Of great benefit to industry was the finding that hoggets and adult sheep were relatively resistant to the clinical effects of OJD. Even though infection occurred, ewes rarely succumbed to the disease while hoggets were more resistant than lambs. This means that hoggets (median age in this study 22.5 months) and adult sheep can be used to graze contaminated pasture with less risk of clinical impact compared to lambs, and so these classes of sheep can be used to prepare pasture for lambs. Pasture spelling should also be useful. Conventional wire strand fences do not prevent spread of infection so disease control needs to be based on an area-wide approach. 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. 2005-06-01T00:00:00Z http://hdl.handle.net/2123/949 Title: Modelling of OJD : extension of project to include economic analysis and preparation of an existing package. Authors: Sergeant, Evan Abstract: Under MLA Project OJD.027, the pathogenesis, epidemiology and options for control of Johne's disease in sheep were reviewed and mathematical models developed to simulate the spread of Johne’s disease within infected flocks, and between flocks on a regional basis. The models also allow the evaluation and comparison of various control options at both flock and regional levels. These models were completed during 2002, and a final report on the project prepared for MLA. However, for these models to be effectively used as an aid to the control of OJD in Australia, it is essential that managers and advisers involved in the OJD program at State and local levels are familiar with the models and with the predicted effects of various control strategies, at both farm and regional level. At the farm level, information on the predicted effect and cost-benefit of various strategies will assist advisers in formulating effective and efficient control strategies for individual farmers. Similarly at local and State/Regional level, the output of the regional spread model and simulated control strategies will assist disease managers to make informed decisions about preferred control options for OJD. 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. 2003-04-01T00:00:00Z http://hdl.handle.net/2123/948 Title: Validation of the gamma-interferon test for ovine Johne's disease. Authors: Stewart, David J Abstract: In theory, the interferon-γ (IFN) test has potential for improved control of ovine Johne’s disease (OJD) by early detection before contamination of pasture and transmission of infection. To validate the IFN test, a project has been completed for determining specifity and sensitivity. Because of nonspecific IFN responses, raised cut-points were required to achieve high specificity (≥98%). This resulted in reduction of sensitivity to below 50%, limiting its application for early detection or certification from disease freedom. The assay may have application in a test and cull program as a surrogate test for faecal shedding and the removal of sheep with severe disease but this approach to control of OJD will require further confirmation. A major limitation for adoption is the widespread use of vaccination precluding the use immunological tests for diagnosis. Other limitations, apart from relatively low sensitivity, include cost of the test as well as a narrow window of ~6 hours between the commencement of blood sample collection and laboratory initiation of the assay so that test result validity is not compromised. Thus, in its current format, it is unlikely, that the IFN assay, apart from possibly stud flocks, will have wide application in the sheep industry. 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. 2005-09-29T00:00:00Z http://hdl.handle.net/2123/947 Title: Ewe-lamb transmission of ovine Johne's Disease. Authors: NSW Agriculture. Elizabeth Macarthur Agricultural Institute Abstract: Knowledge of the likelihood of intrauterine or transmammary transmission of M. a. paratuberculosis infection in sheep is important in the design of control programs. Little has been published on this aspect of ovine Johne's disease, although studies in cattle have found up to 25% of foetuses from clinically affected cows to be infected. In this study 151 ewes from heavily infected flocks and their late term foetuses were examined using all available antemortem and necropsy tests. Five of six ewes with clinical OJD had infected foetuses. One of 54 subclinically affected ewes and none of 16 apparently uninfected ewes had infected foetuses. Only two ewes (both clinical cases which also had infected foetuses) had detectable M. a. paratuberculosis in their milk or mammary glands. Thus, although intrauterine or transmammary transmission may occur frequently in clinically affected sheep, it is infrequent in subclinically infected ewes or in ewes not detectably infected (even if from a heavily infected flock), suggesting that this mode of transmission is unlikely to significantly affect existing OJD control programs. 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. 2003-04-01T00:00:00Z http://hdl.handle.net/2123/946 Title: Study of the biological and economic impact of OJD in affected sheep flocks in NSW : 12 farm mortality study. Authors: Toribio, Jenny-Ann; Bush, Russell; Windsor, Peter Abstract: This study provides industry with factual information about the impact of OJD on farms in southern Australia. This is needed to assess the magnitude of the OJD problem and to direct control and management programs. On 12 farms, the average annual OJD mortality rate based on inventory records from 2002-2004 was 6.8% (range 1.8% to 17.5%), well above the accepted annual mortality rate (from all causes) for Australian sheep flocks. OJD losses accounted on average for 70% (range 17% to 100%) of the estimated total financial loss associated with sheep deaths in 2002. In addition this project confirmed that prevalence based on pooled faecal culture (PFC) could be used as an indicator of OJD mortality level and provided support for further investigation of several risk factors in a larger future study (MLA OJD.038). The gross margin model developed provides estimates of on-farm cost of OJD and of vaccination control for wool and sheep-meat enterprises including break-even points for vaccination at various prevalence levels. We recommend that producers, through industry extension activities, be informed of the substantial losses associated with OJD and be encouraged to apply the model to support decision making regarding OJD control. 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. 2005-09-01T00:00:00Z http://hdl.handle.net/2123/945 Title: Evaluation of PFC and AGID as flock-screening tests for OJD : National Ovine Johne's Disease Control and Evaluation Program. Authors: Sergeant, E. S. G Abstract: The aims of this project were to provide comparative estimates of the flock-sensitivity of PFC and AGID under a range of likely scenarios, using a simulation approach. Sample sizes required to achieve equivalent performance of PFC and AGID under different conditions of prevalence and desired flocksensitivity were also estimated, as well as the effect of variations in the assumptions on which the model was based. The resulting Monte Carlo simulation model indicated (amongst other recommendations) that PFC should be the preferred screening test for surveillance and market-assurance testing for ovine Johne’s disease in Australia, although the AGID may be an appropriate alternative where prevalence is likely to be high or where a rapid result is required. 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. 2001-11-01T00:00:00Z http://hdl.handle.net/2123/944 Title: Individual animal tests for ovine Johne's disease. Authors: Reddacliff, L. A; Whittington, R. J Abstract: Routine diagnostic tests for ovine paratuberculosis have poor sensitivity in the early stages of the disease, and transmission often occurs before detection. Currently there are no tests to accurately confirm early infection in individual sheep. Such tests are required to provide trading opportunities for producers who may have valuable stock at low risk of infection. Surgical biopsy is one means of disease detection using relatively sensitive laboratory procedures, but was unproven. 77 sheep grazing on a heavily infected farm were examined at 12, 18 and 24 months of age by histopathology and culture of biopsied ileum and mesenteric lymph nodes. Results from biopsy were compared to those from routine tests (ELISA, AGID, IFN-γ, skin testing, faecal culture and direct PCR) applied at six-monthly intervals, and to necropsy findings at three years of age. A total of 170 biopsies were performed without serious complications, and the samples collected were adequate for culture and histological assessment of paratuberculosis. Overall, 36% of sheep were shown to be uninfected at 3 years of age. Of these, 16 were uninfected at all sampling times and 11 sheep had recovered. (ie. They had been infected at an earlier sampling.) The remaining 64% of sheep were classified at necropsy as infected. Biopsy was consistently the most sensitive nonlethal technique for identification of infected sheep, although even at 36 months it detected only 2/3 of infected sheep. It may be useful as an additional tool in the management for individual valuable sheep from infected stud flocks. 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. 2004-03-01T00:00:00Z http://hdl.handle.net/2123/943 Title: National Workshop on Control Strategies : a review of the NSW approach. 17 and 18 April, 2001 – AMA House, Barton ACT. Authors: National Ovine Johne’s Disease Control and Evaluation Program Abstract: The purpose of this workshop was to facilitate a structured discussion by national and state OJD technical advisers of a number of proposals for change to the on-farm strategies currently applied in NSW for controlling the spread of OJD, particularly within and from high disease prevalence areas. A number of resolutions involving control strategies, vaccine use, sheep identification and permitted sheep movements, property disease management, OJD Control zoning, approved tests and infected property profiling were passed. 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. 2001-01-01T00:00:00Z http://hdl.handle.net/2123/942 Title: Cross species transmission of Ovine Johne's Disease - Phase 2 cattle. Authors: Moloney, B. J; Whittington, R. J Abstract: One thousand seven hundred and seventy four cattle from 12 properties were sampled by ELISA and faecal culture to detect Johne’s Disease. All properties had a known significant history of Johne’s disease in sheep. They were mostly selected from participants in NOJDP Trial 1.1 (a study to examine the effectiveness of an eradication strategy) and had cattle known to be susceptible to JD at the time that their properties were infected with OJD. All gave negative results on serology; only one animal from a herd of 349 gave a single positive faecal culture result, with all follow-up investigations being negative, suggesting passive transfer of the organism. Due to the small size of some of the herds tested, and the fact that no confirmed infected animals or herds were detected, it is not possible to give maximum estimate of the prevalence of OJD in exposed susceptible cattle. However, using information derived from previous investigations and some additional results in the addendum to this project report, it is known that there are at least 6 cattle herds infected with “S” strain, in NSW, at the present time. 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. 2002-09-01T00:00:00Z http://hdl.handle.net/2123/941 Title: Field evaluation of the tracer weaner model : early detection of sheep with Mycobacterium avium subsp. paratuberculosis. Authors: NSW Agriculture. Elizabeth Macarthur Agricultural Institute Abstract: Experiments were conducted on two separate farms in the endemic area for OJD to determine whether tracer animals could be used to detect infective levels of S strain M. a. paratuberculosis on pasture. Culture from tissues was shown to be the most sensitive method for the detection of early infection in sheep after natural exposure to S strain M. a. paratuberculosis. The organism was detected in at least one naive introduced sheep from every potentially exposed group, 6 to 12 months post-exposure. Antemortem diagnostic tests (skin testing, IFN-γ and faecal culture) were shown to have low sensitivity at this early stage of naturally acquired disease. The prevalence of infection early after exposure was similar in sheep first exposed as neonates, as weaners or as adults. Lambs born from an infected flock became tissue culture-positive sooner than naive lambs suckling uninfected ewes introduced to the same infected environment. These findings suggested that groups of naive sheep, used as tracer animals and tested by tissue culture at slaughter after 6 months exposure, might be useful to assess pasture infectivity in disease control programs. 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. 2002-11-01T00:00:00Z http://hdl.handle.net/2123/940 Title: Assessing the risks of transmitting OJD in the semen of rams by artificial insemination. Authors: Central Tablelands Rural Lands Protection Board Abstract: The impact on stud breeders of the current national program to limit the spread of OJD within the Australian sheep industry could be reduced if they could safely use semen from within their studs. Trading semen would be a means of maintaining some cash flow, and artificial insemination could be used to re-establish the studs’ genotype within any destocking program. This research has shown for the first time that semen collected from rams clinically infected with OJD can contain M Ptb, the bacteria that causes OJD, and that it is likely that bacteria could be transferred to the reproductive tract of ewes at mating or AI. These results indicate that quality assurance guidelines for the safe use of semen from infected flocks need to be developed further. 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. 2000-12-01T00:00:00Z http://hdl.handle.net/2123/939 Title: National field evaluation of pooled faecal culture - interim report 24 October 00. Abstract: Pooled faecal culture (PFC) has been proposed as a screening test for testing sheep populations as part of the NOJDP as it provides the potential for significant savings for the NOJDP compared with serological testing. Doubts having arisen about the specificity and robustness of the technique and its performance in areas of Australia outside New South Wales, it was deemed necessary to have the PFC undertaken in several laboratories, drawing samples from flocks from a variety of regions (in Western Australia, South Australia, Tasmania, Victoria and Queensland) with both positive and negative status. PFC testing was effectively performed in participating laboratories as indicated by ANQAP proficiency testing and the results of the field evaluation, including the testing of positive and negative controls. PFC was found to have the anticipated high sensitivity for detecting infected flocks with only one known infected flock with negative results in the trial. Negative PFC results were reported for 76 farms (699 pools) which had a flock history or testing record which indicated no evidence of OJD. 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. 2000-10-24T00:00:00Z http://hdl.handle.net/2123/938 Title: Survival of Johne’s Disease in the environment : National Ovine Johne's Disease Control and Evaluation Program. Authors: Whittington, R. J Abstract: This report covers three MLA projects (TR.055, TR.055A and OJD.003) undertaken by NSW Agriculture to determine how long the sheep strain of Mycobacterium paratuberculosis survives in the environment to validate destocking recommendations for eradication of OJD. Survival of the organism was prolonged but finite. In the shade it lasted for 13 months while in the open in ungrazed pasture it lasted for 7 months. It survived for a shorter period in fully exposed pastures where grazing was simulated but for much longer in water than on pasture. These times were probably underestimates. Liming pasture did not reduce survival and moisture did not increase it. Shade was the most significant factor favouring survival. Further research is necessary to determine the mechanisms of survival, which include dormancy. Decay rates for the organism were determined for short term and long term destocking. These can be used to estimate how much time must be allowed to render pastures safe for control and eradication of OJD, respectively. When estimates of soil ingestion rates by grazing sheep are combined with within-flock OJD prevalence estimates and bacterial shedding rates determined by PFC, it is possible to make property by property recommendations for the purpose of control or eradication of OJD. 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. 2001-06-30T00:00:00Z http://hdl.handle.net/2123/937 Title: Evaluation and comparison of two methods of abattoir surveillance for detection of ovine Johne’s Disease. Authors: Denholm, L; Ryan, M; Lugton, I Abstract: This project was designed to determine whether properties infected with ovine Johne’s disease (OJD) could be identified by routine monitoring of cull sheep at abattoirs for lesions of OJD or the presence of Mycobacterium avium subsp. paratuberculosis. Trained inspectors were stationed in abattoirs to examine not less than 50% and up to 95% of the abdominal viscera from all lines of adult sheep slaughtered during each kill shift (about 10 to 15 lines per shift at the two major export abattoirs). Where visible lesions suggestive of OJD were observed, fixed tissue samples were taken for confirmatory histopathology from up to three suspect sheep in each suspect line. Inspectors were not told the identity of the trial lines, but were aware that there was a trial line to be killed during the particular shift. Tied-off loops of terminal ileum were also taken from 10 randomly selected sheep in each line of sheep killed during the shift for pooled intestinal culture (PIC). The results of this trial indicate that visual and tactile monitoring of the viscera of cull sheep at slaughter for lesions suggestive of ovine Johne’s disease is a highly sensitive and reliable strategy for the detection of OJD infected flocks in which deaths from OJD are occurring. 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. 2001-06-01T00:00:00Z http://hdl.handle.net/2123/936 Title: Field evaluation of OJD control using Gudair. Authors: Reddacliff, Leslie Abstract: A 5-year field trial was undertaken to determine the efficacy of a killed M. a. paratuberculosis vaccine, GudairTM, for the control of OJD in Australian merinos. The vaccine stimulated cellmediated and humoral immune responses. Gudair™ reduced mortalities due to OJD by 90% and delayed faecal shedding for the first year post-vaccination (pv). Thereafter, the prevalence of shedders among vaccinates was reduced by 90%. The numbers of M. a. paratuberculosis excreted by the vaccinated groups were also reduced by at least 90% at most sampling times. However, high levels of excretion by vaccinates occurred on some occasions, and although only 7 of 600 vaccinates died from OJD, all had multibacillary disease. Thus there remains a risk that some vaccinated sheep could transfer the disease. Small reductions in liveweight gain were found in vaccinated lambs in the first year pv, but there was little effect on condition score or wool production. Vaccine injection site lesions were detected in almost 50% of sheep 2 months pv, and these persisted for at least 4 years in 20-25% of vaccinates. Data from this trial enabled the registration of Gudair™ in Australia in 2002 and underpins the pivotal role of vaccination in the current management of OJD. 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. 2005-05-01T00:00:00Z http://hdl.handle.net/2123/935 Title: Cross species transmission of ovine Johnes Disease - Phase 1 : National Ovine Johne’s Disease Control and Evaluation Program. Authors: Whittington, R. J; Taragel, C. A Abstract: Johne’s disease was investigated in fibre goats on several farms. The disease was caused by sheep [S] strains of Mycobacterium avium subsp. paratuberculosis. The infection appeared to be less severe than the same infection in sheep in that fewer goats than sheep became infected, and fewer goats than sheep developed obvious signs of the infection. However, infected goats shed the organism in their faeces and therefore were able to spread the infection to other goats and sheep. Therefore inclusion of goats in the control program for ovine Johne’s disease is justified. A communication program is recommended to advise producers that ovine Johne’s disease in goats may not be obvious and that testing should be undertaken to ensure disease is not present. The impact of ovine Johne’s disease on the fibre goat industry is projected not to be great due to the small number of herds likely to be infected. 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. 2000-06-01T00:00:00Z http://hdl.handle.net/2123/933 Title: Evaluation of eradication strategies for ovine Johne's Disease. Authors: Taylor, Pat; Webster, Stewart Abstract: Johne’s disease, caused by Mycobacterium avium subspecies paratuberculosis (Mptb), is spreading through domestic and non-domestic populations of ruminants worldwide. Ovine Johne’s Disease (OJD) is considered to be a relatively new disease in Australia (25 – 50 years) that at present has infected less than 10% of sheep flocks nationally. The great majority of infected flocks are concentrated around a number of foci of infection in the southern mainland and adjacent islands. OJD is highly infectious but difficult to detect early in the cycle of infection because of a lengthy incubation period (2 – 3 years) and insensitive tests for sub-clinically infected sheep. Currently there is international debate among gastroenterologists and microbiologists regarding Mptb’s involvement in the aetiology of Crohne’s disease in humans. In 1998 steering committees representing the sheep industries and state and federal governments agreed on a national program of regulation, education and research to contain and improve our understanding of the epidemiology and pathology of OJD under Australian conditions. Whole of flock destocking and restocking was considered to be one potential strategy to prevent further spread of the disease and underpin systematic regional eradication campaigns. This report presents the results of a field evaluation of the biological efficacy and economic viability of destocking and restocking strategies to eradicate OJD from farms in south eastern Australia. Of 41 flocks that were monitored for three years after restocking decontaminated farms, 28 (68%) presented with evidence of OJD. Among these (re)infected farms there was a substantial reduction in mean apparent prevalence between destocking and three years after restocking. Although equivocal, eradication failures appear to have been primarily of local origin (ie reinfection from neighbouring flocks and/or incomplete decontamination). Because of low efficacy, 20 year simulations of net farm income revealed that destocking and restocking was less profitable than vaccination as an OJD management option. 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. 2005-02-01T00:00:00Z