Forecasting clinical disease in pigs: comparing a naive and a Bayesian approach

In veterinary practice the clinician often evaluates and predicts herd health status over time according to clinical criteria. In this paper, we modeled three different clinical signs among pigs based on longitudinal clinical observations in 15 pig herds. We compared and discussed the outputs from two different approaches for making clinical forecasts in a herd: a naive approach using a simple time series model with previous disease observations as predictors and a Bayesian state space models approach, in which the time lag variable entered into the random component of the model. We used the Markov chain Monte Carlo technique to calculate posterior distributions of the forecasts. For the herd specific forecasts the results showed that there were only minor differences between the forecasts from the simple time series model and the median forecasts from the Bayesian model. However, the credibility intervals from the Bayesian model were wider than the forecasts from the simple model and, therefore the Bayesian model encompassed the variability in the forecasts better. Compared to the statistical model, the simple time series would be easier to implement in a practical setting. However, the latter lacks the inherent “generality” from the statistical model that allows the user to make statements about the distribution of the herds and to predict disease status based on the “average” correlation among the herds. The applicability of the Bayesian approach within a clinical decision-making framework was discussed, with special emphasis on the use of prior information and clinical forecasting.     

The Ontario Animal Health Network: enhancing disease surveillance and information sharing through integrative data sharing and management

The Ontario Animal Health Network (OAHN) is an innovative disease surveillance program created to enhance preparedness, early detection, and response to animal disease in Ontario. Laboratory data and, where available, abattoir condemnation data and clinical observations submitted by practicing veterinarians form the core of regular discussions of the species-sector networks. Each network is comprised of government veterinarians or specialists, epidemiologists, pathologists, university species specialists, industry stakeholders, and practicing veterinarians, as appropriate. Laboratorians provide data for diseases of interest as determined by the individual network, and network members provide analysis and context for the large volume of information. Networks assess data for disease trends and the emergence of new clinical syndromes, as well as generate information on the health and disease status for each sector in the province. Members assess data validity and quality, which may be limited by multiple factors. Interpretation of laboratory tests and antimicrobial resistance trends without available clinical histories can be challenging. Extrapolation of disease incidence or risk from laboratory submissions to broader species populations must be done with caution. Disease information is communicated in a variety of media to inform veterinary and agricultural sectors of regional disease risks. Through network engagement, information gaps have been addressed, such as educational initiatives to improve sample submissions and enhance diagnostic outcomes, and the development of applied network-driven research. These diverse network initiatives, developed after careful assessment of laboratory and other data, demonstrate that novel approaches to analysis and interpretation can result in a variety of disease risk mitigation actions.     

Veterinary medical manpower: supply-demand projections to 2020.

A supply projection model to estimate the number of veterinarians available through the year 2020 was developed. When projected available manpower was compared with the need for veterinary medical services, as estimated in a National Academy of Science study, a net shortage was indicated in each year between 1976 and 2020. The manpower supply available if 3 additional veterinary colleges were developed in the United States was also estimated. It was concluded that, even with the additional output of these colleges, the supply of veterinarians will not keep pace with future needs for veterinary services.     

Estimation of heritability for Tying-up syndrome in the Thoroughbred racehorse by Gibbs sampling

Tying‐up is a condition that primarily affects the muscles of horses. In this study, the heritability of the Tying‐up syndrome in the Thoroughbred racehorse was estimated by Bayesian analysis with Gibbs sampling based on the threshold model for binary traits. The data used were the clinical data in racehorses diagnosed by veterinarians of the Racehorse Clinics of Japan Racing Association from 2000 to 2003. The health status of the Tying‐up was treated as a binary trait. In the genetic analysis, the effect of changing the amount of the pedigree or inbreeding information on the estimation of heritability was investigated, too. The heritability estimates with non‐zero probability in the posterior densities were approximately 0.16–0.18 in minimum, suggesting that the heritability of the Tying‐up is not zero at least. The posterior density distributions of the heritability estimates were generally more pointed and sharp with using inbreeding coefficients than without using it, suggesting that more stable estimations were obtained when inbreeding coefficients were used. Among the different amounts of pedigree and inbreeding information, the heritabilities obtained with three or four generations of pedigree using inbreeding coefficients seems to be preferable, i.e. heritability of 0.42 or 0.43 for Tying‐up.     

Attitudes, procedures, and delivery of behavior services by veterinarians in small animal practice

OBJECTIVE: To survey veterinarians in small animal practice concerning their attitudes about delivery of behavior services, frequency of common behavior problems, manner in which services were provided, confidence in their clinical ability to treat these behavior problems, frequency of use of pharmacologic intervention, and number of dogs and cats euthanatized specifically because of behavior problems. DESIGN: Cross-sectional mail survey. SAMPLE POPULATION: Random sample of veterinarians in small animal practice in the United States. PROCEDURE: A self-administered mail survey was sent to a random sample of 2,000 veterinarians. Results were tabulated and statistically analyzed. RESULTS: It was estimated that approximately 224,000 dogs and cats were euthanatized annually in small animal veterinary practices in the United States because of behavior problems. Although veterinarians seemed unwilling to euthanatize animals for behavior problems solely on the basis of a client's request, many veterinarians did not routinely inquire about animal behavior and often were not confident in their clinical skills to treat behavior problems. Female veterinarians tended to be more proactive in addressing behavior problems and to have more positive attitudes than male veterinarians about the importance of animal behavior. CONCLUSIONS AND CLINICAL RELEVANCE: Efforts are needed to increase the number of veterinarians who systematically incorporate inquiries about animal behavior into routine clinical practice and to build the confidence of veterinarians for diagnosing and treating animal behavior problems.     

A survey of zoonotic diseases contracted by South African veterinarians

A survey of 88 veterinarians employed at the Faculty of Veterinary Science, University of Pretoria, South Africa, was carried out to investigate the occurrence of zoonotic diseases among South African veterinarians. The survey found that 63.6% of veterinarians interviewed had suffered from a zoonotic disease. Veterinarians predominantly involved in farm animal practice were 3 times more likely to have contracted a zoonotic disease than those working in other veterinary fields. Fifty-six percent of disease incidents were initially diagnosed by the veterinarians themselves. Fifty-three percent of incidents required treatment by a medical practitioner, but the majority (61%) of incidents did not require absence from work. The incidence density rate for contracting a zoonotic disease was 0.06 per person year of exposure. Kaplan-Meier survival analysis estimated that the probability of having contracted a zoonotic disease was 50% after 11 years in practice. The risk of contracting a zoonotic disease appeared to be higher early in practice. The most common mode of transmission was by direct contact. Approximately 46% of South Africans still live in rural areas and regularly come into close contact with farm animals. The implications of this in the light of this survey's results are discussed.     

Use of participatory epidemiology to compare the clinical veterinary knowledge of pastoralists and veterinarians in East Africa

Because of severe resource and logistical constraints in large areas of Africa, disease surveillance systems need to maximize the use of information provided by livestock keepers and make correct interpretations of indigenous livestock knowledge. This paper describes the use of participatory epidemiology (PE) to compare the names, clinical signs and epidemiological features of cattle diseases as perceived by pastoralists and veterinarians. Using results from two previous studies with pastoralists in southern Sudan and Kenya, provisional translations of local disease names into modern veterinary terminology were used to develop a matrix scoring method for use with veterinarians. Matrix scoring data from pastoralists and veterinarians were then compared using simple visual comparison of summarized matrices, hierarchical cluster analysis and multidimensional scaling. The results showed good agreement between pastoralists' and veterinarians' disease names and diagnostic criteria. The matrix scoring method was easy to use and appropriate for use in under-resourced areas with minimal professional support or laboratory services. Matrix scoring could be used to assist livestock disease surveillance workers to design surveillance systems that make better use of pastoralist's indigenous knowledge and correctly interpret local disease names. The method should be combined with conventional veterinary investigation methods where feasible.     

Epidemiological and genetical studies in Norwegian pig herds. I. Design of a disease recording system

The study was based on 70 pig herds in the south-eastern part of Norway during the period from 1984 to 1986. The purpose was to design a health card system based on individual disease records covering diseases in sows, piglets and slaughter pigs. It is concluded that individual health records on a herd basis may well be suited for use in epidemiological and genetical studies of disease frequencies and disease resistance. Feedback of results to farmers and veterinarians seems to be important for satisfactory follow-up in the herds.     

Training veterinary personnel for effective identification and diagnosis of exotic animal diseases

The requirements for exotic animal disease (EAD) training were considered at a workshop organized for those with responsibilities for EAD response management in the different states of Australia, with the objective of identifying the optimum strategy for training veterinarians to identify and act upon EADs. It was concluded that there should be specialized within-country training in EAD recognition for an elite group of diagnostic veterinarians who are required to recognize the major exotic diseases of animals, instigate the correct procedures to confirm the diagnosis of the disease, and undertake appropriate measures for effective initial management of the disease. The use of live, deliberately infected animals for demonstration purposes is not currently supported by any research indicating an improved learning outcome compared with that from alternatives, such as videos, necropsy specimens, and dedicated computer-aided learning packages. Therefore, ethical requirements to minimize the use of animals in teaching and research may prevent live-animal use. It is concluded that training should take place within each country via a course of instruction that includes an initial intensive course followed by continued professional development, with examination of knowledge at the end of each.     

Bayesian analysis to validate a commercial ELISA to detect paratuberculosis in dairy herds of southern Chile

In Chile, Mycobacterium avium subsp. paratuberculosis (Map) has been isolated on several occasions and clinical cases have been reported. Nevertheless, diagnostic tests have not yet been validated for this agent in the Chilean setting. The objective of the study was to validate a commercial ELISA to detect Map shedding dairy cows in management conditions, prevalence and stages of infection existing in Southern Chile, utilising different statistical approaches. Blood and faeces were collected from 1333 lactating cows in 27 dairy herds (both large commercial and smallholder dairy farms) between September 2003 and August 2004. Within the herds up to a maximum of 100 dairy cows were selected based on age (>or=3 years old) and, if present, clinical signs of a Map infection. In herds with less than 100 cows, all cows >or=3 years old were sampled. Blood samples were tested using a commercial ELISA kit (IDEXX Laboratories, Inc.). Faecal samples were cultured on Herrold's Egg Yolk Medium (HEYM). Latent class models (i.e. maximum likelihood (ML) methods and Bayesian inference) were used to determine the validity of the ELISA. Map was cultured from 54 (4.1%) cows and 10 (37.0%) herds, which were all large, commercial dairy herds. As a result of empty cells in the cross-tabulations, the ML model provided the same results as the validation with faecal culture as the gold-standard. In the Bayesian model, the Se and Sp of the ELISA were estimated to be 26% (95% CI: 18-35%) and 98.5% (95% CI: 97.4-99.4%), respectively. For faecal culture, the Se was 54% (95% CI: 46-62%) and the Sp was 100% (95% CI: 99.9-100%). Interestingly, the prevalence in the smallholder dairy farms was estimated to be 8% even though there were no faecal culture positive cows detected in those herds. There was no significant correlation between the two tests. The advantage of Bayesian inference is that the Se and Sp of both tests are obtained in one model relative to the (latent) true disease status, the model can handle small datasets and empty cells and the estimates can be corrected for the correlation between tests when the tests are not conditionally independent. Therefore, Bayesian analysis was the preferred method for Map that lacks a gold-standard and usually has low cow-level prevalence.     

Carriage of methicillin-resistant Staphylococcus aureus by veterinarians in Australia

Objective To estimate the prevalence of carriage of methicillin‐resistant Staphylococcus aureus (MRSA) among Australian veterinarians. Methods Individuals attending veterinary conferences in Australia in 2009 were recruited to provide nasal swabs and complete a questionnaire about their professional activities. Swabs were processed by standard methods for detecting MRSA and questionnaire responses were used to group veterinarians according to their areas of major work emphasis (species and practice type). Prevalence was estimated for each of these grouping and contingency tables and regression tree analysis used to explain the variation in MRSA carriage. Results Among the 771 respondents ‘industry and government veterinarians’ (controls) had the lowest prevalence of MRSA carriage at 0.9%. Veterinarians with horses as a major area of work emphasis had a prevalence of 11.8% (13‐fold that of controls) and those whose only major emphasis was horses had a prevalence of 21.4% (23‐fold that of controls). Veterinarians with dogs and cats as a major activity had a 4.9% prevalence (5‐fold that of controls). Prevalence rates for other major activities (pigs, dairy and beef cattle, avian and wildlife) were also increased, but were estimated from smaller numbers of respondents. Regression tree analysis clearly isolated equine veterinarians and dog and cat practitioners as groups at increased risk of carriage of MRSA. Conclusion Carriage of MRSA is a notable occupational health issue for veterinarians in clinical practice in Australia, particularly those who work with horses.     

Estimation of distance related probability of animal movements between holdings and implications for disease spread modeling

Between holding contacts are more common over short distances and this may have implications for the dynamics of disease spread through these contacts. A reliable estimation of how contacts depend on distance is therefore important when modeling livestock diseases. In this study, we have developed a method for analyzing distant dependent contacts and applied it to animal movement data from Sweden. The data were analyzed with two competing models. The first model assumes that contacts arise from a purely distance dependent process. The second is a mixture model and assumes that, in addition, some contacts arise independent of distance. Parameters were estimated with a Bayesian Markov Chain Monte Carlo (MCMC) approach and the model probabilities were compared. We also investigated possible between model differences in predicted contact structures, using a collection of network measures.We found that the mixture model was a much better model for the data analyzed. Also, the network measures showed that the models differed considerably in predictions of contact structures, which is expected to be important for disease spread dynamics. We conclude that a model with contacts being both dependent on, and independent of, distance was preferred for modeling the example animal movement contact data.     

A Bayesian elicitation of veterinary beliefs regarding systemic dry cow therapy: variation and importance for clinical trial design

The two key aims of this research were: (i) to conduct a probabilistic elicitation to quantify the variation in veterinarians' beliefs regarding the efficacy of systemic antibiotics when used as an adjunct to intra-mammary dry cow therapy and (ii) to investigate (in a Bayesian statistical framework) the strength of future research evidence required (in theory) to change the beliefs of practising veterinary surgeons regarding the efficacy of systemic antibiotics, given their current clinical beliefs. The beliefs of 24 veterinarians in 5 practices in England were quantified as probability density functions. Classic multidimensional scaling revealed major variations in beliefs both within and between veterinary practices which included: confident optimism, confident pessimism and considerable uncertainty. Of the 9 veterinarians interviewed holding further cattle qualifications, 6 shared a confidently pessimistic belief in the efficacy of systemic therapy and whilst 2 were more optimistic, they were also more uncertain. A Bayesian model based on a synthetic dataset from a randomised clinical trial (showing no benefit with systemic therapy) predicted how each of the 24 veterinarians' prior beliefs would alter as the size of the clinical trial increased, assuming that practitioners would update their beliefs rationally in accordance with Bayes' theorem. The study demonstrated the usefulness of probabilistic elicitation for evaluating the diversity and strength of practitioners' beliefs. The major variation in beliefs observed raises interest in the veterinary profession's approach to prescribing essential medicines. Results illustrate the importance of eliciting prior beliefs when designing clinical trials in order to increase the chance that trial data are of sufficient strength to alter the clinical beliefs of practitioners and do not merely serve to satisfy researchers.     

Opinions and practices of veterinarians and dairy farmers towards herd health management in the UK

The objective was to compare farm veterinary surgeons' and dairy farmers' opinions on herd health plans and herd health and production management with the aim of discovering and better understanding the differences. Two comparable questionnaires, one for farm veterinarians and one for dairy farmers, were distributed throughout the UK. While listing the 'major roles' of the veterinarian on the farm, veterinarians considered 'optimising milk production', 'decreasing overall cost' and 'being an independent adviser' as important roles, but these were not seem to be perceived as such by the farmers. In addition, when presenting themselves to clients, veterinarians seemed to favour the 'friend of the farmer' approach; a much smaller proportion of farmers seemed to prefer this approach. The majority of farm respondents (98 of 121; 81 per cent) valued the discussions with their veterinarian, and it was apparent from the relatively small proportion of veterinarians instigating a discussion on farm (33 of 125; 26 per cent) that there is the opportunity for a more proactive approach from veterinarians. The study underlines that 'demonstrating cost-effectiveness' is still a main concern for veterinarians and farmers and identifies areas that can be improved by more training and effective communication.     

An Epidemiological Survey of Therapy and Diagnostic Procedures Used by Norwegian Small Animal Practitioners in Cases of Nasal Mite (Pneumonyssoides caninum) Infection in Dogs

Forty per cent of the members of the Norwegian Small Animal Veterinary Association (NSAVA) returned a questionnaire regarding the treatment and diagnosis of canine nasal mite infection in their practices in 1996. A total of 2392 dogs were treated for this infection by 156 NSAVA members in clinical practice in that year, averaging 15.3 treated dogs per veterinarian. An estimated minimum of 6000 Norwegian dogs were treated for nasal mite infection in 1996, at an estimated cost of treatment exceeding 3.3 million NOK. Fifty-nine per cent of the practitioners included at least a case history and clinical examination as diagnostic criteria prior to initiating treatment for nasal mite infection. Fewer than 10% routinely performed more thorough diagnostic procedures, and only 1.8% of the diagnoses were verified prior to treatment. A total of 27 different treatment regimens, involving either subcutaneously injected ivermectin or orally administered milbemycin oxime, were routinely used by NSAVA veterinarians to treat these dogs. Seventy-two (53%) of the veterinarians used ivermectin exclusively, 14 (10%) used milbemycin oxime exclusively, while 50 (37%) used both ivermectin and milbemycin oxime. No other drugs were used. Evaluation of treatment was made by assessing resolution of the clinical signs following treatment, and 97% of the veterinarians were satisfied with the effect of the treatment regimen they used. Adverse side-effects following treatment for nasal mite infection in 1996 were seen on 9 occasions; 4 following ivermectin administration and 2 following milbemycin oxime treatment, while in 3 cases no information on the drug used was provided. The risk of adverse reactions to treatment of nasal mite infection in dogs was 0.4%.     

Estimation of economic loss associated with anaplasmosis in California beef cattle

On the basis of questionnaire surveys and personal interviews with veterinarians, ranchers, and livestock farm advisors, the seriousness of anaplasmosis in California was determined. In 1976, the economic loss due to anaplasmosis in the study sample of beef cattle was $2,203,150. When inferences were made from the sample population to include the whole population of beef cattle, this loss was estimated to be $5,244,319. These values were in contrast to a farm advisors' estimate of $11 million loss due to anaplasmosis, which was included in a total estimated loss of $300 million due to all livestock diseases of economic importance in California. It appeared that anaplasmosis, although having a substantial economic impact in California, is not as economically devastating as it was once thought to be. It was concluded that private programs currently in use (vaccination and treatment) are sufficient to control anaplasmosis.     

Accurate genomic predictions for BCWD resistance in rainbow trout are achieved using low‐density SNP panels: Evidence that long‐range LD is a major contributing factor

Previously accurate genomic predictions for Bacterial cold water disease (BCWD) resistance in rainbow trout were obtained using a medium‐density single nucleotide polymorphism (SNP) array. Here, the impact of lower‐density SNP panels on the accuracy of genomic predictions was investigated in a commercial rainbow trout breeding population. Using progeny performance data, the accuracy of genomic breeding values (GEBV) using 35K, 10K, 3K, 1K, 500, 300 and 200 SNP panels as well as a panel with 70 quantitative trait loci (QTL)‐flanking SNP was compared. The GEBVs were estimated using the Bayesian method BayesB, single‐step GBLUP (ssGBLUP) and weighted ssGBLUP (wssGBLUP). The accuracy of GEBVs remained high despite the sharp reductions in SNP density, and even with 500 SNP accuracy was higher than the pedigree‐based prediction (0.50–0.56 versus 0.36). Furthermore, the prediction accuracy with the 70 QTL‐flanking SNP (0.65–0.72) was similar to the panel with 35K SNP (0.65–0.71). Genomewide linkage disequilibrium (LD) analysis revealed strong LD (r² ≥ 0.25) spanning on average over 1 Mb across the rainbow trout genome. This long‐range LD likely contributed to the accurate genomic predictions with the low‐density SNP panels. Population structure analysis supported the hypothesis that long‐range LD in this population may be caused by admixture. Results suggest that lower‐cost, low‐density SNP panels can be used for implementing genomic selection for BCWD resistance in rainbow trout breeding programs.     

Marine anemia in farmed chinook salmon (Oncorhynchus tshawytscha): Development of a working case definition

Marine anemia (plasmacytoid leukemia) is a histologically defined syndrome affecting farmed chinook salmon (Oncorhynchus tshawytscha) in British Columbia, Canada. Although the disease has received recent attention and has been diagnosed in many fish farms, past criteria for diagnosis have limited the depth and breadth of epidemiological investigations. By identifying a repeatably diagnosable subset of signs and symptoms of affected fish, a new working case definition of marine anemia was developed. This definition relied exclusively on histological features to achieve the diagnosis. The intra-observer repeatability of diagnoses using the new definition was high ( κ = 0.84). An algorithm employing gross pathological signs was created for field investigation of the disease. The algorithm was capable of predicting histological diagnosis with a reasonable level of accuracy, and was judged to be a valuable tool for diagnostic decisions. We concluded that by using the case definition created in this study together with the algorithm, the comparability and accuracy of clinical and epidemiological research of marine anemia could be improved.     

Intra- and inter-observer agreement of a protocol for clinical examination of dairy cows

In 2004,five veterinarians examined 283 dairy cows from four Danish dairy herds and independently assigned scores for the clinical signs lameness, hock lesions and other cutaneous lesions to each cow using a clinical protocol. We evaluated the inter-observer and the intra-observer agreement using prevalence-adjusted, bias-adjusted kappa (PABAK). We chose two different cut-offs between the ordinal scores for classifying cows as healthy or diseased for each of the clinical signs, and we compared the ability of the observers to discriminate between healthy and diseased cows for the two cut-offs. Without any formal training of the observers we found PABAK in the range 0.36-0.88 and we concluded that the choice of cut-off had an effect on the observed agreement among the observers.     

Improving understanding of early behavioral indicators of lumbosacral disease in working dogs using 3D visualization of skeletal movements during working tasks: Feasibility study

An improved understanding of the early behavioral indicators of lumbosacral disease in working dogs may allow earlier interventions and help reduce premature retirement because of disability. However, recognition of early behavioral indicators can be challenging in stoic, high-drive working dogs because they often mask clinical signs. The purpose of this feasibility study was to develop a technique for visualizing canine skeletal movements during working tasks and to describe veterinary clinical specialist opinions on the utility of the visualization technique. Three detection-trained police dogs with a recent history of working task deficits and suspected lumbosacral disease were recruited for the study. Conventional and motion capture video recordings were acquired as dogs performed walking and search high working tasks. Whole-body computed tomography (CT) scans were acquired using clinical multislice CT scanners. Image data from motion capture recordings and whole-body CT scans were analyzed and merged. Three-dimensional (3D) computer animation video clips of skeletal movements were created for each dog and each task, using multiple viewing angle perspectives. Interactive meetings with veterinary clinical specialist reviewers were used to refine point placements for the final renderings. Veterinary clinical specialists reviewed final 3D animation movie clips and recorded their opinions on the utility for the visualization technique. Veterinary clinical specialists reported that the computer animations helped them recognize behavioral characteristics that they had not initially noticed in physical examinations. Potential applications for this visualization technique include creating educational training aids for veterinary students, owners, and handlers; assisting veterinarians in planning rehabilitative treatments; and assisting researchers in developing computer models for biomechanical analyses. Future controlled prospective studies are needed in a large number of normal and affected working dogs to improve accuracy of the visualization technique and test the effect of the technique on observer performance.