Identification of risk factors for OJD infection-level in sheep flocks.

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

Zoonotic disease risk perceptions and infection control practices of Australian veterinarians: Call for change in work culture

This study was conducted to determine the perceptions of zoonotic disease risk among Australian veterinarians, the infection control practices they use to protect themselves from zoonotic diseases, and the factors influencing their use of these protective practices. A questionnaire was designed and piloted prior to its administration to veterinarians at the annual Australian Veterinary Association Conference in May 2011. The questionnaire comprised 21 closed, semi-closed and open questions. Data from the questionnaire were analyzed using ordinal logistic regression analyses to determine significant factors for veterinarians’ use of personal protective equipment (PPE). A total of 344 veterinarians completed the questionnaire of which 63.7% were women, 63.2% worked in small/companion animal practice, and 79.9% worked in private veterinary practice. Of the respondents, 44.9% reported contracting a zoonosis during their careers with 19.7% reporting a suspected case and 25.2% reporting a confirmed incidence. Around 40–60% of veterinarians perceived exposure to zoonosis likely or very likely in a variety of situations. With reference to current national industry guidelines, the reported use of PPE was less than “adequate” for most scenarios except for performing postmortems, surgery or dental procedures. No PPE was used by 60–70% of veterinarians for treating respiratory and neurological cases and by 40–50% when treating gastrointestinal and dermatological cases. Workplace conditions need improvement as 34.8% of workplaces did not have isolation units for infected animals, 21.1% did not have separate eating areas for staff, and 57.1% did not have complete PPE kits for use. Veterinarians were more likely to use PPE if they had undertaken postgraduate education, perceived that zoonosis exposure from animals and procedures was likely, consciously considered PPE use for every case they dealt with and believed that liability issues and risks encouraged use of PPE. In contrast, those working in private practices, those who tended to ‘just hope for the best’ when trying to avoid zoonotic diseases, and those who were not aware of industry guidelines were less likely to use PPE. The results suggest that veterinarians’ perceptions and workplace policies and culture substantially influence their use of PPE. Efforts should be made to encourage veterinarians and their workplaces to use infection control practices to protect themselves and their staff from zoonotic diseases

The use of a modified Delphi approach to engage stakeholders in zoonotic disease research priority setting

Background After the 2011 cluster of Hendra virus cases in horses in Australia, public health targeted education initiatives at people in the equine industry to reduce human exposure to potentially infected horses. ‘Horse owners and Hendra Virus: A Longitudinal cohort study To Evaluate Risk’ aims to enhance public health measures through improved understanding of Hendra virus risk perception and risk mitigation strategies among horse owners and horse care providers. This paper describes the stakeholder consultation that was undertaken to ensure the cohort study outcomes were relevant to diverse groups who play a role in Hendra virus policy development and implementation. Methods A two-round modified Delphi study with online questionnaires was conducted. In round one, stakeholders identified priority research areas. In round two, stakeholders rated and ranked topics that emerged from thematic analysis of the round one responses. Round two data were analysed using logistic regression. Results Of the 255 stakeholders contacted, 101 responded to round one. Over 450 topics were proposed. These were organized into 18 themes. Approximately two thirds of the round one respondents participated in round two. ‘Hendra virus-related risk awareness and perception’, ‘personal health and safety’, ‘emergency preparedness’, ‘risk prevention, mitigation, and biosecurity’, and ‘Hendra virus vaccination in horses – attitudes/uptake’ were the top five areas identified according to probability of being ranked extremely important. Conclusions In this study, a modified Delphi approach was effective in guiding research into Hendra virus, a zoonotic disease of animal and human health significance. The findings support the notion that stakeholders should be engaged in zoonotic disease research priority setting. Such consultation will help to ensure that research initiatives are relevant and useful to stakeholders in the position to make use of new findings. Keywords Delphi method Stakeholder engagement Zoonotic disease Hendra virus Public health Thematic analysisThis research was funded by the Commonwealth of Australia, the State of New South Wales and the State of Queensland under the National Hendra Virus Research Program

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

Speculation about the association of soil characteristics with the expression of ovine Johne’s disease (OJD) prompted this cross-sectional study. We enrolled 92 sheep flocks in Australia during 2004-05 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 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. Keywords: risk factors, paratuberculosis, mycobacterium, cross-sectional study, organic carbon, clay, sand, pH, iron.Meat and Livestock Australi

Risk factors for ovine Johne's disease in infected sheep flocks in Australia

We conducted a cross-sectional study in 2004-05 to investigate risk factors for ovine Johne’s disease (OJD) involving 92 infected Merino sheep flocks in Australia. In each enrolled flock we collected pooled faecal-samples from 3- to 5-year-old sheep and cultured them for Mycobacterium avium subsp. paratuberculosis (MAP) to determine their OJD status. Based on pooled faecal-culture (PFC) results, three outcome variables representing different facets of disease biology were derived: pool OJD status (binomial: positive or negative), log pool MAP number (continuous) and cohort OJD prevalence level (ordinal: low (10%) prevalence). We used these outcomes in three separate multivariable analyses to identify risk factors, which were based on a questionnaire administered during a face-to-face interview with the farmer. We found higher OJD infection in sheep whose dams had been in poor condition and kept at a high stocking rate during lambing and in sheep which had experienced a longer period of growth retardation during their lifetime. Flocks that had vaccinated for >2 years (rather than only 1 to 2 years) with a killed MAP vaccine had significantly lower OJD infection. In addition, practices including culling low body-weight sheep or selling sub-flocks experiencing high losses, sharing of roads between neighbouring farms, and greater frequency of application of super-phosphate fertilizers were associated with higher OJD. Of the confounders investigated, infection was higher in flocks experiencing high mortalities; in wethers compared to ewes; and in 3-year-old sheep compared to 4-year-old sheep. Keywords: risk factors, paratuberculosis, ovine Johne’s disease, Australia, Mycobacterium, epidemiology, cross-sectional studyMeat and Livestock Australi

A Bayesian Approach to Estimate OJD Prevalence From Pooled Fecal Samples of Variable Pool Size

This paper describes a Bayesian approach to prevalence estimation based on pooled samples that accommodates variation in pool size and adjusts for test imperfection. A logistic model was developed for pooled fecal culture (PFC) sensitivity as a function of pool size and a logistic mixed model for ovine Johne’s disease (OJD) prevalence as a function of covariates that were found significant in a recent OJD risk factor study conducted in Australia. Available data on these factors and prior information about prevalence and sensitivity were incorporated into a Bayesian model to estimate OJD prevalence from PFC data. Overall, posterior cohort OJD prevalence was estimated to be 0.16 (range of prevalences across cohorts 0.002 to 0.72). The average prevalence was higher in wethers than ewes. PFC sensitivities for pool sizes 10, 30 and 50 were estimated to be 0.91 (95% probability intervals 0.80, 0.96), 0.85 (0.80, 0.90) and 0.77 (0.65, 0.88), respectively. Posterior specificity of PFC was almost perfect though based primarily on the prior. Results suggest the Bayesian model successfully estimated the animal-level prevalence after accounting for variable pool size and imperfect test parameters. The method can be easily adapted for other conditions and diseases where pooled samples are collected. WinBugs code for the article is available online. Key Words: Diagnostic test Mycobacterium Ovine Johne’s disease Paratuberculosis Prevalence Sensitivit

Estimation of sensitivity and flock-sensitivity of pooled faecal culture for Mycobacterium avium subsp. paratuberculosis in sheep

Pooled faecal culture (PFC) is a widely used test in ovine Johne’s disease (OJD) control programmes in Australia but information about its characteristics is limited. We conducted this study to estimate sensitivity and flock-sensitivity of PFC in sheep with different OJD histopathological lesions in simulated flocks with a range of infection prevalence levels. Initially, a known quantity of faeces from sheep with pauci- or multi-bacillary lesions was pooled with uncontaminated faeces from confirmed non-infected sheep and cultured using PFC technique. PFC sensitivity, calculated as a proportion of the pools of a particular size that tested positive, was determined to be 90% in sheep with the multibacillary form of the disease but varied with pool size in sheep with the paucibacillary form of OJD. Subsequently, probabilistic models were developed to estimate overall pool-sensitivity achieved in a flock (Sek) and flock-sensitivity of PFC (FSe) in various simulated scenarios. In flocks with a given ratio of multi- to pauci-bacillary sheep and with low to moderate infection prevalence level, Sek decreased with increase in pool size, but increased with pool size in flocks with ≥ 10 % prevalence. FSe, in contrast, increased with pool size in all the tested scenarios. Both Sek and FSe increased with infection prevalence, ratio of multi- to pauci-bacillary sheep and the number of pools sourced from flocks. Sensitivity analyses indicated that the estimates and trends were robust to moderate changes in input parameters. The results suggest that the current testing of seven pools of size 50 is adequate for most scenarios, however, for very low prevalence flocks, a gain in FSe can be made by increasing the number of pools tested and a higher Sek can be achieved by reducing pool sizes. Keywords: pooling, paratuberculosis, ovine Johne’s disease, Australia, Mycobacterium, epidemiology.Meat and livestock australi

Horse owners' biosecurity practices following the first equine influenza outbreak in Australia

A cross-sectional study was conducted involving 759 Australian horse owners to determine their biosecurity practices and perceptions one year after the 2007 equine influenza outbreak and to investigate the factors influencing these perceptions and practices. A web link to an online questionnaire was sent to 1224 horse owners as a follow-up to a previous study to obtain information about biosecurity perceptions and practices, impacts of the 2007 EI outbreak, demographic information and information about horse industry involvement. Ordinal logistic regression analyses were conducted to determine factors associated with poor biosecurity practices. Biosecurity compliance (low, medium, high), as determined by horse owners’ responses to a 16-item question on the frequency of various biosecurity measures, was used as the outcome variable in ordinal logistic regression analyses. Variables with a univariable p-value ≤0.2 were eligible for inclusion in multivariable models built using a manual stepwise approach. Variables with a p-value <0.05 in multivariable models were retained in the final model. Two potential confounders - age and gender of participants- were included in the final model irrespective of their p-values. Thirty percent of the respondents had low biosecurity compliance and were performing biosecurity practices ‘not very often’ or ‘never’. Younger people, people with two or more children, those who were not involved with horses commercially and those who had no long-term business impacts resulting from the 2007 EI outbreak were more likely to have lower biosecurity compliance. People who were not fearful of a future outbreak of equine influenza in Australia and those who thought their current hygiene and access control practices were not very effective in protecting their horses also had poor biosecurity practices. In this observational study we identified factors associated with a group of horse owners with low levels of biosecurity compliance. As this cross-sectional study only assesses associations, the identified factors should be further investigated in order to be considered in the design of extension activities to increase horse owners’ biosecurity compliance. Keywords: Biosecurity; Equine; Owner perceptions; Ordinal logistic regression