Jeff Eppleston

Association of farm soil characteristics with ovine Johne's disease in Australia

Speculation about the association of soil characteristics with the expression of ovine Johnes disease (OJD) prompted this cross-sectional study. We enrolled 92 sheep flocks in Australia during 2004-2005 and in each enrolled flock collected pooled faecal samples from an identified cohort (group of same age and sex) of sheep and soil samples from the paddocks grazed by this cohort of sheep. Faecal pools were cultured to create three outcome variables: positive or negative status of faecal pools (pool OJD status, binary); the log number of viable Mycobacterium avium subsp. paratuberculosis (MAP) organisms per gram of faeces (log pool MAP number, continuous); and the prevalence of faecal shedders (cohort OJD prevalence level, ordinal: low <2%, medium 2-10% and high >10%). Separate statistical models were then developed to investigate the association between soil characteristics and each outcome variable. Sheep raised on soils with a higher percentage of organic carbon and clay had a higher OJD prevalence whereas, sheep grazing on soils with a higher content of sand and nitrogen had a lower OJD prevalence. Iron content of the soil was positively associated with OJD infection but the association between soil pH and OJD was inconclusive. Parent soil type, the only farm level factor, was not significant in any of the final models. Study results indicate a higher risk of OJD in sheep raised on soils with greater organic matter and clay content. We hypothesise that this is due to adsorption of MAP to clay and the consequent retention of the bacteria in the topsoil, thus making them available in higher numbers to grazing sheep.

Comparison of pre- and post-vaccination ovine Johne's disease prevalence using a Bayesian approach

This study was conducted to evaluate the effectiveness of Gudair™ vaccine in decreasing the prevalence of shedding of Mycobacterium avium subsp. paratuberculosis (MAP) in flocks of varying initial prevalence. Thirty-seven self-replacing Merino flocks from New South Wales and Victoria (Australia) that had been vaccinating lambs with Gudair™ for at least five years were enrolled in the study. These flocks had been tested prior to or at commencement of vaccination using pooled faecal culture, agar gel immunodiffusion or both tests. These pre-vaccination test results were used to estimate pre-vaccination prevalence. Post-vaccination prevalence was estimated from culture of usually 7 pools of 50 sheep collected from the enrolled flocks in 2008-2009, approximately five or more years after commencement of vaccination. A Bayesian model was developed to estimate and compare the pre- and post-vaccination prevalences for the enrolled flocks. Apparent pre- and post-vaccination prevalences for flocks were modelled as functions of the true pre- and post-vaccination prevalences, respectively, and the sensitivities and specificities of the respective diagnostic tests. Logit-normal models were specified on pre- and post-vaccination true prevalences and were then used to make inferences about the median and 90th percentile of the prevalence distributions and their differences. Priors were mostly specified based on published literature or analysis of abattoir surveillance data for this population of flocks. The analysis found a significant decline in ovine Johnes disease prevalence from a pre-vaccination median prevalence of 2.72% [95% probability interval (PI): 1.40; 6.86%] to a post-vaccination median prevalence of 0.72% (0.39; 1.27%). However 30 of the 37 flocks still contained sheep that were shedding MAP in their faeces. The results suggest that vaccination with Gudair™ is usually effective in reducing the prevalence of faecal shedding but the response to vaccination is variable among flocks. The Bayesian approach reported here could be implemented in similar situations to compare prevalences where information from multiple diagnostic tests with varied sensitivities and specificities is available.

Lesions in sheep following administration of a vaccine of a Freund's complete adjuvant nature used in the control of ovine paratuberculosis.

Abstract CASE HISTORIES: Occurrences of adverse reactions in seven sheep flocks in Australia following vaccination against paratuberculosis where veterinary attention was requested are reviewed. All cases occurred within the 3-year period following commencement of use of a vaccine of a Freunds complete adjuvant nature, at a time when approximately six million doses of vaccine had been administered. CLINICAL FINDINGS: In the first case, 26/58 (45%) Merino sheep vaccinated as adults had palpable tissue reactions at or near the site of vaccination; enlarged prescapular lymph nodes were palpated in 17 (29%), and nine (16%) sheep had both palpable lesions at the site of vaccination and enlarged prescapular lymph nodes. The reactions included caseous nodules up to 5.5 cm in diameter. In the other cases, fistulating or granulomatous wounds were occasionally found at the recommended site of injection behind the ear, and myiasis was rare. Occurrences of inappropriate choice of injection site were recorded, including injection into the axilla of two Merino rams, and lesions in the tissues of the maxilla and nose of almost 50% of 350 Border Leicester lambs. Four outbreaks of progressive paralysis due to injection into cervical musculature were reported, described as ‘OJD staggers’ by producers. DIAGNOSIS: Granulomatous cellulitis and lymphadenitis associated with oil droplets typical of ‘oil granulomata’. Injection of vaccine into the dorsal cervical area resulted in progressive paralysis due to myonecrosis and suspected granulomatous leptomeningitis. CLINICAL RELEVANCE AND CONCLUSIONS: Although lesions at and near the site of injection are common, adverse reactions to vaccination were rare and included mortality from cervical spinal injection, production losses from injection in the maxilla or axilla or if myiasis resulted, and potential marketing losses if animals or carcasses are discounted as a result of the lesions. Risk factors for adverse reactions included inadequate restraint of sheep, breed of sheep, experience of the operator, poor injection technique, and inappropriate placement of vaccine. Increasing attention to the proper restraint of animals, restricting vaccination to the recommended site behind the ear, careful placement of the vaccine into subcutaneous tissue to avoid drainage of vaccine material into tissues such as the spinal cord, and post-vaccination supervision to address welfare concerns should adverse reactions occur are recommended.

Effectiveness of Gudair™ vaccine for the control of ovine Johne's disease in flocks vaccinating for at least 5 years.

OBJECTIVE Examine the prevalence of shedding of Mycobacterium avium subsp. paratuberculosis (Mptb) at least 5 years after starting vaccination with Gudair™ in flocks of varying initial prevalence of ovine Johnes disease (OJD) and identify risk factors for variation in vaccine efficacy. METHODS Pooled faecal culture (PFC) was conducted for 41 flocks from southern NSW and Victoria to determine estimates of current OJD prevalence. The data were compared to estimates of prevalence at or prior to commencement of vaccination at least 5 years earlier, based on available serological or PFC tests when vaccination commenced. A cross-sectional study was conducted to identify risk factors for differing prevalence levels in 36 of the flocks. RESULTS Historical data enabled classification of 37 flocks as high (13; 35.1%), medium (10; 27.0%) or low (14; 37.8%) estimated initial OJD prevalence. Results of PFC in 2008-09 identified that 81.1% (30/37) of flocks had detectable shedders, with 48.6% (18/37) flocks still classified as medium or high OJD prevalence, including 50% (7/14) of flocks initially classified as low prevalence. Shedding was not detected in 18.9% (7/37) flocks. Flocks with OJD prevalence exceeding 1% at 5 years or more following the commencement of vaccination were associated with reports of sheep straying and introduction of new sheep. CONCLUSION Despite significant declines in estimated OJD prevalence following vaccination for ≥5 years, 81.1% of flocks were shedding Mptb and considered at risk of spreading the disease or suffering recrudescence of losses if vaccination were to cease. Flock managers are advised to persist with vaccination.

Effect of unvaccinated Merino wether lambs on shedding of Mycobacterium avium subspecies paratuberculosis in flocks vaccinating for ovine Johne's disease

OBJECTIVE To determine the prevalence of Mycobacterium avium subspecies paratuberculosis (Mptb) shedding by unvaccinated wethers compared with vaccinated ewes. METHODS Six self-replacing, ovine Johnes disease (OJD)-infected Merino flocks that had been vaccinating lambs with Gudair(TM) for at least 5 years, but had not vaccinated their last two drops of wethers were studied. Faecal samples were collected in pools of 50 from 350 vaccinated ewes (1-2 years old) and from 350 unvaccinated wethers of the same age and were cultured to determine the presence of viable Mptb. RESULTS The estimated prevalence of shedding sheep among the unvaccinated wethers was 6-fold greater than among the vaccinated female siblings (0.21% vs 1.27%), with faecal pools collected from unvaccinated wethers being 19-fold more likely to be positive than those from the vaccinated ewes. CONCLUSION Leaving wethers unvaccinated is likely to considerably increase pasture contamination with Mptb and potentially jeopardise disease control.

Association of microsatellite polymorphisms with immune responses to a killed Mycobacterium avium subsp. paratuberculosis vaccine in Merino sheep

Abstract AIM: To study the association of polymorphisms at five micro-satellite loci with immune responses to a killed Mycobacterium avium subsp. paratuberculosis (Map) vaccine. METHODS: Merino sheep (504 vaccinates and 430 unvaccinated controls) from a long-term Johnes vaccine trial undertaken on three different properties in the Central Tablelands of New South Wales, Australia, were genotyped for five micro-satellite markers located in three immunologically significant chromosome regions. The marker loci included three from the major histocompatibility complex (MHC), namely DYMS1, OLADRB and SMHCC1; and one each from the solute carrier family 11 member 1 (SLC11A1), OVINRA1, and the interferon-γ (IFN-γ), o(IFN)-γ, gene regions. Associations between immune responses and genetic polymorphisms at the marker loci were examined by analysing both allelic and genotypic effects. RESULTS: The o(IFN)-γ locus had only two alleles, whereas the other four loci exhibited extensive polymorphism, with the number of alleles ranging from 10 (OVINRA1) to 21 (DYMS1), resulting in 30–92 genotypes per locus. Heterozygosities varied between 37% (o(IFN)-γ) and 87% (SMHCC1), while information on polymorphic contents ranged from 0.31 (o(IFN)-γ) to 0.87 (DYMS1). Each of the three properties exhibited unique allelic and genotypic frequencies. Analysis of immune response data revealed strong antibody and IFN-γ responses as early as 2 months post-vaccination. Immune responses in control animals on all three properties remained consistently low, except for slightly elevated IFN-γ responses at a few time-points on two properties, concomitant with exposure to natural infection. Genotype-phenotype association analyses revealed a number of marker geno types/alleles to be significantly associated with antibody and IFN-γ responses. However, the effects of only five genotypes (one each at DYMS1, OLADRB, SMHCC1, OVINRA1 and o(IFN)-γ) and three alleles (one each at o(IFN)-γ, DYMS1 and OLADRB) on IFN-γ responses were consistent across the three properties. CONCLUSION: Considering the significance of IFN-γ responses in protection against Map, it is possible that the genotypes/alleles identified might have a role in protective immune responses to natural Map infections, and further studies are warranted to confirm this.

The prevalence of lice (Bovicola ovis) in sheep flocks on the central and southern Tablelands of New South Wales

In response to suggestions that the incidence of louse infestations in New South Wales has increased markedly, a survey of 173 producers was conducted in the Tablelands Livestock Health and Pest Authority region using visual detection and a questionnaire to document retrospective lice history. An estimated apparent prevalence of 16.5% is a moderate increase from the 10% reported in 2004. On a subset of the surveyed sheep flocks sheep, lice-specific immunoassay conducted by the New South Wales Department of Primary Industries were used to detect low levels of infestation that were not identified by visual detection. This provided a true prevalence estimate of 30%. These results will be used to promote improved control and preventative strategies.

Changes in prevalence of ovine paratuberculosis following vaccination with Gudair®: Results of a longitudinal study conducted over a decade

Since its registration in 2002, Gudair® vaccine has become the key tool for managing paratuberculosis in sheep in Australia. This study was conducted to evaluate its effectiveness in reducing paratuberculosis prevalence in 12 flocks over more than one decade. Flocks with variable initial prevalence (5, 4 and 3 with low, medium, and high prevalence, respectively) were enrolled in the study in 2003-04. Six biennial faecal samplings were conducted in these flocks over a 10year period. At each sampling, faeces from four age groups (3, 4, 5 and 6year-old sheep) were collected from each flock. The aim was to select 7 or 14 pools of faeces constituted with pellets from 50 or 25 sheep from each age group, respectively, but the numbers and sizes of pools did vary due to logistical issues. Samples were cultured using pooled faecal culture approach and sheep level paratuberculosis prevalence was estimated. Changes in probability of a pool being positive and in paratuberculosis prevalence over time were evaluated by fitting generalised-linear and linear mixed models. The proportion of positive faecal pools significantly declined over time from 50.3% at the first sampling in 2003-04 to only 3.1% at the last sampling in 2013-14, suggestive of a 30-fold reduction in the odds of a pooled faecal sample to be positive (p<0.001). Similarly, the average animal level prevalence in flocks dropped from 7.64% at the first sampling to 0.12% at the last sampling. However, faecal shedding persisted and was still present in 3 of the 8 flocks (37.5%) that remained in the study at the last sampling conducted in 2013-14. This is the longest study ever conducted to evaluate paratuberculosis vaccine effectiveness. The results will enable sheep producers to make informed decisions on managing paratuberculosis, and in evaluating the risks of purchasing and trading vaccinated sheep.

Foot abscess in sheep: Evaluation of risk factors and management options.

Foot abscess of sheep is a painful, suppurative and necrotic infection of the phalanges and interphalangeal joints. Sheep affected by foot abscess may be acutely lame and pregnant ewes may die with secondary pregnancy toxemia when they fail to maintain their required level of nutrition. We conducted a cross-sectional observational study to identify and quantify possible risk factors for foot abscess. A questionnaire was designed and used to conduct telephone interviews with 115 sheep farmers in the Central Tablelands of NSW in November 2012. They were asked to provide information on their farm, the animals, and management-related information for the lambing period of a selected cohort of ewes. Multivariable logistic regression analyses were conducted using two outcome variables: (a) the presence of foot abscess, and (b) low (<1%), medium (between 1% and 5%) or high (>5%) levels of foot abscess. High levels of clover in the paddocks grazed by sheep was associated with increased odds of foot abscess in both the models (binary model odds ratio [OR]: 3.18; 95% confidence interval [CI]: 1.22, 8.77 and ordinal model OR: 2.92; 95% CI: 1.35, 6.54). High risk was also associated with the farmers observation that it had been a wet season (ordinal model OR: 7.89, 95% CI: 2.72, 24.43) and moving sheep during lambing (binary model OR: 14.15, 95% CI: 2.30, 296.61). Similarly, farms with shale/slate type soils had lower odds of the disease compared to farms with basalt-derived soils. Farmers who used foot-baths (binary model OR: 4.05, 95% CI: 1.15, 19.34) and antibiotics (ordinal model OR: 3.16, 95% CI: 1.38, 7.66) had higher odds of foot abscess, as might be expected as they adopted these measures to deal with an increased prevalence of foot abscess. The findings from this study can be used to provide extension advice to farmers and for designing further confirmatory studies.