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PubMed1998

Ovine Johne's disease: the risk associated with sheep imported into Western Australia.

OBJECTIVE: To assess the risk of Johne's disease not being detected in sheep imported from New South Wales into Western Australia. DESIGN: A stochastic simulation model. PROCEDURE: The process of importing sheep was broken down into steps and numbers or probabilities assigned to each. Controls on the movement of sheep included surveillance tests in source flocks and serological tests on sheep in consignments before and after transportation to Western Australia. The model calculated the risk of occurrence of Johne's disease in Western Australia and the success of the agar gel immunodiffusion test in identifying consignments with infected sheep. RESULTS: Negative surveillance tests in source flocks reduced the risk to about one twentieth of that when no surveillance tests were required. On average, Johne's disease was predicted to be introduced once in every 3 to 7 years when no testing of either the source flock or the sheep in consignments was required. When negative surveillance tests only were required the interval increased to once in every 63 to 111 years and, with the additional requirement that all sheep in each consignment must have a negative test before and after transport, the interval further increased to once in every 125 to 333 years. When only sheep in consignments were tested, the interval was calculated to be 8 to 14 years. CONCLUSION: A requirement that imports be derived from flocks which had negative surveillance tests to Johne's disease would provide significantly greater protection for the sheep industry in Western Australia.

Animals↗
PubMed2001

Ovine Johne's disease in Australia--the first 20 years.

OBJECTIVE: To review the history of ovine Johne's disease in Australia. PROCEDURE: Relevant publications and reports were identified and reviewed to document the spread of ovine Johne's disease (OJD) from 1980 until the end of 2000, as well as the response of industry and government to the spread of this disease. RESULTS: OJD was first diagnosed in the central tablelands region of New South Wales in 1980. Since then it has spread, either from the initial focus or through separate introductions so that by December 2000 a total of 823 infected flocks had been identified. Cases have been confirmed in New South Wales, Victoria, the Australian Capital Territory, on Flinders Island in Tasmania, on Kangaroo Island in South Australia and in Western Australia. In early 1999, agreement was reached to fund and implement a 6-year, $40 million National OJD Control and Evaluation Program (NOJDP). This program is jointly funded by the sheep industries (national and state), and Commonwealth and State governments, and is managed by Animal Health Australia. CONCLUSION: A national program is now in place to support the control of OJD and research to determine the feasibility and cost-effectiveness of eradication. The development of new diagnostic techniques, such as abattoir surveillance and pooled faecal culture, provide opportunities to refine surveillance strategies and to define better the distribution and prevalence of this disease, as required by the national program. Effective control measures, combined with quality surveillance data, will enable informed decision making for the future national management of OJD.

Animals↗
PubMed2002

The estimated prevalence of Johne's disease infected sheep flocks in Australia.

OBJECTIVE: To estimate the likely geographical distribution and flock-prevalence of ovine Johne's disease (OJD) in Australia. DESIGN: A cross-sectional study design was used. PROCEDURE: 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. RESULTS: 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 these estimates about 6 to 10% of flocks in New South Wales and 2.4 to 4.4% of flocks Australia-wide are likely to be infected. CONCLUSION: This study suggests that OJD has a highly clustered distribution in Australia, and provides estimates of the prevalence of infected flocks by State or region. Based on this analysis there were probably between 2000 and 3700 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. Some States, such as Queensland and Western Australia, may have a prevalence equal or close to 0%, however the technique used was unable to demonstrate the absence of infection in these States with the intensity of surveillance undertaken to date.

Abattoirs↗
PubMed2004

Cross-sectional study of risk factors for the clinical expression of ovine Johne's disease on New South Wales farms.

OBJECTIVE: To explore the environmental and management risk factors that promote the clinical expression of ovine Johne's disease on farms in New South Wales. DESIGN: Cross-sectional study. PROCEDURE: A questionnaire about the farm, flock and their management was mailed to all farmers known to keep infected sheep in the area zoned residual for ovine Johne's disease in New South Wales. The resultant data were analysed by multivariate statistical methods, specifically examining the factors associated with farmers reporting some mortality due to ovine Johne's disease; the reported annual incidence of ovine Johne's disease-associated mortality; the youngest age at which sheep die from ovine Johne's disease; whether scouring was a feature of the disease; and the season of peak mortality from ovine Johne's disease. RESULTS: Fine wool Merino sheep were more likely to die from ovine Johne's disease than other sheep types. Mortality was higher on farms with light sandy soils and those with a high proportion of improved pastures containing subterranean clover. Winter shearing was also associated with clinical expression. The time that the infection had been present on a farm was not strongly associated with mortality. Higher stocking density, high rainfall and access to open water, factors that are believed to aid transmission, were not found to be influential. CONCLUSION: Clinical expression appears to be principally associated with light infertile soils and their associated pastures and pasture improvement practices which may lead to micronutrient deficiencies or imbalances. Genetic effects are also important and are likely to be exacerbated by physiological stressors, such as winter shearing.

Animal Husbandry↗
PubMed2004

Effect of a test and control program for bovine Johne's disease in Victorian dairy herds 1992 - 2002.

OBJECTIVE: To report on progress in Johne's disease (JD) control in infected dairy herds participating in the Victorian Johne's disease Test and Control Program (TCP). PROCEDURE: Clinical histories and JD testing data recorded by the Department of Natural Resources and Environment (now called Department of Primary Industries) were analysed for 542 dairy herds participating in the TCP. The herds were required to conduct annual herd tests of cattle 2 years old and older with an enzyme linked immunosorbent assay (ELISA), cull the reactors and manage the younger cattle to minimise infection. RESULTS: Testing of over 680,000 animals identified over 10,000 reactors giving an average prevalence of reactors at the first whole-herd test (T1) of 1.78%. There was a relatively rapid increase in the incidence of clinical disease before the TCP started and then it markedly declined. There was a slow and interrupted decline in reactor prevalence, with a marked peak occurring at the fourth herd test (T4). The average age of reactors and clinical cases was 5.7 and 5.9 years, respectively. Of the reactors and clinical cases detected during the TCP, 87% and 95% respectively, were born before the TCP started. Thirty herds completed the program by achieving three successive negative whole herd tests and 91 herds dropped out because of inability to comply with the agreed requirements of the program. There were no home-bred reactors born after the start of the program in 253 (47%) herds and of the 522 herds that were tested more than once, there were 319 (61%) herds in which no home-bred reactors were detected after the first year of testing. The number of ELISA positive animals detected at T1 appeared to be only about 26% of the animals from that round that subsequently became positive or developed clinical disease at later test rounds. CONCLUSION: The TCP caused a marked decline in the number of clinical cases, probably because animals in which clinical disease was imminent were detected by testing and removed. A reduction in prevalence of reactors occurred only when most herd members were born after the TCP started. The sensitivity of the ELISA appears to be low based on the large number of reactors that were negative at T1 but were positive at later tests. Low sensitivity of diagnostic tests and the long incubation period of the disease limits meaningful analysis of the program until it has continued for some years. Measures adopted in the TCP have not broken the cycle of infection in many participating herds. It is unsure if this was because of poor compliance with control recommendations or a poor understanding of methods of transmission by scientists. Eradication is not feasible in the short-term.

Animals↗
PubMedDate not supplied

Effect of compliance with recommended calf-rearing practices on control of bovine Johne's disease.

OBJECTIVE: To assess the degree of compliance with recommended management procedures for the control of bovine Johne's disease and study the relationship between aspects of calf management and testing/disease outcomes in the herds. PROCEDURE: Fifty-four south Gippsland dairy herds participating in the Victorian bovine Johne's disease test and control program were visited between July and November 2002 and an audit of calf rearing practices was conducted. The results of testing completed under the program were analysed for each of the herds. Twenty seven management factors were examined for a relationship with the presence of clinical cases of Johne's disease or cattle with positive ELISA test results that were born after the completion of the second whole herd test. Logistic regression was used to examine the strength of relationships between the management practices and the frequency with which new cases of Johne's disease arose. RESULTS AND CONCULSIONS: Calves were removed from their dams within 12 hours of birth in only 17 (31.5%) of the herds. However, in all but one herd the calves were removed within 24 hours of birth. In 42 herds (77.8%) calf rearing facilities were adequately separated from adult cattle and the faeces from adult cattle. In 41 herds (75.9%) calves up to the age of 12 months were grazed on paddocks that were free of manure or effluent from adult cattle. However, in only 10 (18.5%) of the herds were all three of these calf management practices applied. Feeding whole milk containing antibiotic residues, or providing water for calves from birth, were found to have statistically significant associations with an increased occurrence of cases of bovine Johne's disease in the study herds. The practice of allowing cows to calve in a paddock was found to be associated with reduced occurrence of bovine Johne's disease. These associations were still found after analysis that included herd size, the number of clinical cases that had occurred in the herds before the start of testing, the number of animals with positive ELISA tests that were detected at the first test and the number of years of participation in the test and cull program. Early separation of newborn calves from cows and grazing calves under 12 months of age in areas free of adult cattle were not found to be protective against Johne's disease.

Animal Husbandry↗
PubMed2006

Losses of adult sheep due to ovine Johne's disease in 12 infected flocks over a 3-year period.

OBJECTIVE: To measure the biological and financial impact of ovine Johne's disease (OJD) mortalities on 12 infected flocks within the endemic area of southern New South Wales over a 3-year period. DESIGN AND POPULATION: An observational study was conducted over a 3-year period from 2002 to 2004 on sheep from 12 OJD-infected flocks from southern NSW. Flocks ranged from between 3,500 and 20,000 sheep. At the start of the study owner estimates of OJD mortality were 5% or greater. METHOD: Annual mortality rates were estimated from farm records provided by owners. The proportion of OJD mortalities was assessed after histological examination of tissues collected from dead and moribund sheep during 5-day necropsy inspections conducted in autumn, winter, spring and summer in 2002. The financial impact was estimated using a gross margin analysis for each of the three study years and by placing a financial value on the necropsied sheep. RESULTS: On the 12 farms, the average OJD mortality rate was 6.2% (range 2.1% to 17.5%) in 2002, 7.8% (range 1.8% to 14.6%) in 2003 and 6.4% (range 2% to 11.9%) in 2004. The average decrease in gross margin due to OJD infection on a farm in 2002 was 6.4% (range 2.2% to 15.4%), 8.5% (range 3.1% to 15.8%) in 2003 and 7.4% (range 1.5% to 15.4%) in 2004. This equates to an average reduction in annual income of $13,715 per farm per year. OJD losses accounted on average for two thirds of the total estimated financial loss associated with sheep deaths. CONCLUSION: This study demonstrates the significant biological and financial impact of OJD on sheep flocks. These findings are of relevance to all Australian sheep flocks infected or at risk of OJD infection.

Age Distribution↗
PubMed2004

Gamma interferon production by bovine gamma delta T cells following stimulation with mycobacterial mycolylarabinogalactan peptidoglycan.

A large percentage of lymphocytes in the blood of cattle express the gamma delta T-cell receptor, but specific functions for these cells have not yet been clearly defined. There is evidence, however, that human, murine, and bovine gamma delta T cells have a role in the immune response to mycobacteria. This study investigated the ability of bovine gamma delta T cells to expand and produce gamma interferon (IFN-gamma) in response to stimulation with mycobacterial products. Bovine gamma delta T cells, isolated from the peripheral blood of healthy cattle, expanded following in vitro stimulation with live mycobacteria, mycobacterial crude cell wall extract, and Mycobacterium bovis culture filtrate proteins. In addition, purified gamma delta T cells, cocultured with purified monocytes and interleukin-2, consistently produced significant amounts of IFN-gamma in response to mycobacterial cell wall. The IFN-gamma-inducing component of the cell wall was further identified as a proteolytically resistant, non-sodium dodecyl sulfate-soluble component of the mycolylarabinogalactan peptidoglycan.

Animals↗
PubMed1988

Progress in culture and subculture of spheroplasts and fastidious acid-fast bacilli isolated from intestinal tissues.

The efficiency of culture media was compared for the culture and subculture of very slowly growing acid-fast bacilli and spheroplast forms obtained from intestinal tissues of patients with Crohn's disease and ulcerative colitis and from controls without inflammatory bowel disease. Media were developed by modifying a nutrient broth medium based on veal infusion broth and yeast extract. We evaluated the effects of pH and the addition of Tween 80, Dubo oleic albumin complex, an extract from intestinal tissue from a patient with Crohn's disease, horse serum, sucrose, magnesium sulfate, ferrous ammonium sulfate, and sodium citrate. All media contained mycobactin J (2 micrograms/ml). We developed a medium (MG3) which was highly successful in promoting the growth of very fastidious organisms and promoted reversion of spheroplasts to acid-fast rods. MG3 contained veal infusion broth, 1% yeast extract, 10% horse serum, 0.3 M sucrose, 0.2% MgSO4, 0.1% ferrous ammonium sulfate, 0.1% sodium citrate, and 2 mg of mycobactin J per liter. We were able to obtain quantities of organisms sufficient for examination of the organisms by molecular techniques. Successful cultivation of all isolates and reversion of spheroplasts to acid-fast forms encourage further studies of the possibility of a complex association of mycobacteria and Crohn's disease.

Crohn Disease↗
PubMed1992

Biologically distinct subtypes of Mycobacterium avium differ in possession of insertion sequence IS901.

Mycobacterium avium causes disease, principally tuberculosis in immunocompromised individuals. It is the most frequent cause of disseminated infections in AIDS patients in the West. The pathogen is also associated with disease in animals, chiefly birds and livestock, and may be isolated from environmental samples such as soil and water. Analysis of strains of M. avium isolated from clinical, veterinary, and environmental sources for the presence of the mycobacterial insertion sequences IS900 and IS901 demonstrates the specific association of IS901 to animal pathogenic M. avium strains. In contrast, most clinical M. avium strains and all AIDS-derived strains examined so far lacked IS901. Significant differences in the plasmid contents and serotypes of strains with and without IS901 were also found. We therefore suggest that the presence of IS901 divides M. avium into two clearly distinct subtypes with differing host range, virulence, plasmid possession, and serotyping antigens. By using DNA sequence data from IS901 and M. avium DNA, a set of polymerase chain reactions were developed for the specific detection and differentiation of these subtypes.

Animals↗
PubMed1993

Determination of the optimal cutoff value for a serological assay: an example using the Johne's Absorbed EIA.

Traditionally, in order to improve diagnostic accuracy, existing tests have been replaced with newly developed diagnostic tests with superior sensitivity and specificity. However, it is possible to improve existing tests by altering the cutoff value chosen to distinguish infected individuals from uninfected individuals. This paper uses data obtained from an investigation of the operating characteristics of the Johne's Absorbed EIA to demonstrate a method of determining a preferred cutoff value from several potentially useful cutoff settings. A method of determining the financial gain from using the preferred rather than the current cutoff value and a decision analysis method to assist in determining the optimal cutoff value when critical population parameters are not known with certainty are demonstrated. The results of this study indicate that the currently recommended cutoff value for the Johne's Absorbed EIA is only close to optimal when the disease prevalence is very low and false-positive test results are deemed to be very costly. In other situations, there were considerable financial advantages to using cutoff values calculated to maximize the benefit of testing. It is probable that the current cutoff values for other diagnostic tests may not be the most appropriate for every testing situation. This paper offers methods for identifying the cutoff value that maximizes the benefit of medical and veterinary diagnostic tests.

Animals↗