Search

Zeynep Ay Şenyiğit,1 Sinem Yaprak Karavana,1 Derya İlem-Özdemir,2 Çağrı Çalışkan,2 Claudia Waldner,3 Sait Şen,4 Andreas Bernkop-Schnürch,5 Esra Baloğlu1 1Faculty of Pharmacy, Department of Pharmaceutical Technology, Ege University, Bornova, İzmir, Turkey; 2Faculty of Pharmacy, Department of Radiopharmacy, Ege University, Bornova, İzmir, Turkey; 3ThioMatrix, Forschungs-Beratungs GmbH, Innsbruck, Austria; 4Faculty of Medicine, Department of Pathology, Ege University, Bornova, İzmir, Turkey; 5Institute of Pharmacy, Department of Pharmaceutical Technology, University of Innsbruck, Innsbruck, AustriaAbstract: This study aimed to develop an intravesical delivery system of gemcitabine HCl for superficial bladder cancer in order to provide a controlled release profile, to prolong the residence time, and to avoid drug elimination via urination. For this aim, bioadhesive nanoparticles were prepared with thiolated chitosan (chitosan–thioglycolic acid conjugate) and were dispersed in bioadhesive chitosan gel or in an in situ gelling poloxamer formulation in order to improve intravesical residence time. In addition, nanoparticle-loaded gels were diluted with artificial urine to mimic in vivo conditions in the bladder and were characterized regarding changes in gel structure. The obtained results showed that chitosan-thioglycolic acid nanoparticles with a mean diameter of 174.5±3.762 nm and zeta potential of 32.100±0.575 mV were successfully developed via ionotropic gelation and that the encapsulation efficiency of gemcitabine HCl was nearly 20%. In vitro/ex vivo characterization studies demonstrated that both nanoparticles and nanoparticle-loaded chitosan and poloxamer gels might be alternative carriers for intravesical administration of gemcitabine HCl, prolonging its residence time in the bladder and hence improving treatment efficacy. However, when the gel formulations were diluted with artificial urine, poloxamer gels lost their in situ gelling properties at body temperature, which is in conflict with the aimed formulation property. Therefore, 2% chitosan gel formulation was found to be a more promising carrier system for intravesical administration of nanoparticles. Keywords: chitosan–TGA, nanoparticle, gemcitabine HCl, intravesical administration, chitosan, poloxamer, superficial bladder cancer

This study evaluated the effects of (i) increasing the concentration of sulfate in drinking water on dry matter intake (DMI), water intake, ruminal fermentation, and apparent total-tract digestibility, and (ii) water sulfate concentration and bismuth subsalicylate (BSS) dose on in vitro ruminal fermentation. Eight ruminally cannulated beef heifers (382 ± 45 kg) were used in a replicated incomplete 3 × 3 Latin square design. Water treatments contained low (342 ± 29 mg/L; LS), medium (2785 ± 72 mg/L; MS), or high (4948 ± 163 mg/L; HS) sulfate. Ruminal digesta was collected to evaluate water sulfate and BSS dose (0.0%, 0.2%, 0.4%, and 0.6% dry matter) on ruminal H2S production in vitro. Water intake increased linearly as water sulfate concentration increased (p = 0.002), but DMI was not affected. Heifers drinking MS and HS had greater ruminal H2S at 10.5 h after water provision than LS (sulfate × time, p < 0.001). In vitro H2S production (µg and µg/mL of rumen inoculum) increased and plateaued with increasing sulfate (p < 0.001) and was linearly reduced (p < 0.001) by increasing BSS dose. Increasing water sulfate concentrations did not negatively affect water or feed intake but increased ruminal H2S concentrations. Bismuth subsalicylate may reduce H2S production. [ABSTRACT FROM AUTHOR]

A study is made to find whether the effect mediated by prostaglandin E2(PGE2) acting throyugh its EP2 receptor in cultured rat mesangial cells. It is seen in glomerulonephritis, cyclooxygenase 2 (COX-2) appears to suppress the expression of alpha integrins by the increased production of prostaglandin E2 activating its EP3 receptor.

We conducted a systematic review and network meta-analysis to determine the comparative efficacy of antibiotics used to control bovine respiratory disease (BRD) in beef cattle on feedlots. The information sources for the review were: MEDLINE®, MEDLINE In-Process and MEDLINE® Daily, AGRICOLA, Epub Ahead of Print, Cambridge Agricultural and Biological Index, Science Citation Index, Conference Proceedings Citation Index – Science, the Proceedings of the American Association of Bovine Practitioners, World Buiatrics Conference, and the United States Food and Drug Administration Freedom of Information New Animal Drug Applications summaries. The eligible population was weaned beef cattle raised in intensive systems. The interventions of interest were injectable antibiotics used at the time the cattle arrived at the feedlot. The outcome of interest was the diagnosis of BRD within 45 days of arrival at the feedlot. The network meta-analysis included data from 46 studies and 167 study arms identified in the review. The results suggest that macrolides are the most effective antibiotics for the reduction of BRD incidence. Injectable oxytetracycline effectively controlled BRD compared with no antibiotics; however, it was less effective than macrolide treatment. Because oxytetracycline is already commonly used to prevent, control, and treat BRD in groups of feedlot cattle, the use of injectable oxytetracycline for BRD control might have advantages from an antibiotic stewardship perspective. [ABSTRACT FROM AUTHOR]

Vaccination against putative causal organisms is a frequently used and preferred approach to controlling bovine respiratory disease complex (BRD) because it reduces the need for antibiotic use. Because approximately 90% of feedlots use and 90% of beef cattle receive vaccines in the USA, information about their comparative efficacy would be useful for selecting a vaccine. We conducted a systematic review and network meta-analysis of studies assessing the comparative efficacy of vaccines to control BRD when administered to beef cattle at or near their arrival at the feedlot. We searched MEDLINE, MEDLINE In-Process, MEDLINE Daily Epub Ahead of Print, AGRICOLA, Cambridge Agricultural and Biological Index, Science Citation Index, and Conference Proceedings Citation Index – Science and hand-searched the conference proceedings of the American Association of Bovine Practitioners and World Buiatrics Congress. We found 53 studies that reported BRD morbidity within 45 days of feedlot arrival. The largest connected network of studies, which involved 17 vaccine protocols from 14 studies, was included in the meta-analysis. Consistent with previous reviews, we found little compelling evidence that vaccines used at or near arrival at the feedlot reduce the incidence of BRD diagnosis. [ABSTRACT FROM AUTHOR]

Background The temporomandibular joint ( TMJ) forms the junction between the maxilla and mandible. Movement of the jaw and resulting masticatory forces have been extensively studied in the horse; however, less is known about the inter-relationship between this joint and oral and dental pathology. Objectives To determine the association between specific oral and dental pathologies and anatomical variations of the TMJ imaged with computed tomography ( CT) in horses with asymptomatic TMJs. Study design Retrospective cross-sectional study. Methods Horses (n = 201) from three practices with a complete oral examination and skull or upper cervical CT study were reviewed. Age, breed, sex, clinical presentation, oral examination findings, slice width and practice were recorded. Alterations in contour and density of the mandibular condyle, mandibular fossa and intra-articular disc were also documented. Logistic regression, corrected for clustering by practice, was used to determine whether CT anatomical variations were significantly associated with the oral examination findings. Results Horses categorised as having abnormal TMJs were older than those with normal TMJ. Horses with periodontal disease were less likely to have abnormal TMJ findings compared with horses with no oral pathology. In contrast, horses with infundibular disease were more likely to have TMJ abnormalities. Main limitations Due to the cross-sectional nature of the study, it was difficult to establish whether oral pathology preceded TMJ abnormalities. Conclusions Despite examining over 200 horses of varying ages, the biological significance of the observed associations between oral, or dental disease and anatomically appreciable temporomandibular joint disorders remains uncertain. [ABSTRACT FROM AUTHOR]

Background Circulating l-lactate concentration is commonly measured in hospitalized horses by sampling from indwelling intravenous ( IV) catheters. However, there are no published evidence-based recommendations to prevent contamination by lactated Ringer's solution ( LRS). Hypothesis Withdrawing 10 mL of blood from the LRS-containing extension set connected to the IV catheter before obtaining the sample for analysis should be adequate to obtain accurate measurement of blood lactate concentration ( BLC). Animals Thirty-three adult hospitalized horses receiving constant rate infusion of LRS. Methods Immediately after disconnecting the LRS, 5 sequential 5 mL blood samples were obtained by aspiration from an extension set connected to an indwelling IV catheter, followed by 3 samples collected by direct venipuncture of the contralateral jugular vein. Samples were analyzed with 1 portable blood lactate analyzer. A linear mixed model was used to examine differences in lactate concentrations among samples collected from the catheter and by direct venipuncture. Results After considering differences in age, breed, sex, and reason for hospitalization, BLCs were higher ( P < .001) in the first and second 5 mL samples collected through the extension set/catheter than in all other extension set/catheter samples or the direct venipuncture samples. The largest difference observed between the third and subsequent catheter or venipuncture samples was 0.34 mmol/L with an upper 95% CI of 1.12 mmol/L. Conclusions and Clinical Importance Withdrawing 15 mL of blood from a LRS-containing extension set connected to an IV catheter (5.9 mL total volume capacity) before obtaining the sample for blood lactate analysis is suggested to optimize accuracy of BLC measurements. [ABSTRACT FROM AUTHOR]

Fecal nutrients and apparent total tract digestibility (ATTD) were predicted using near-infrared spectroscopy (NIRS) of feces collected from the pen floor or the rectum of feedlot cattle in 2 studies, and pen floor samples were assessed for their ability to predict NEg, ADG, and G:F. In study 1, 160 crossbred beef steers in 16 pens (4 pens per treatment) were fed dry-rolled barley or wheat (89% of diet DM) processed at 2 levels. Study 2 utilized 160 crossbred beef steers in 20 pens (5 pens per treatment) that were fed dryrolled barley with 4 levels of barley silage (0%, 4%, 8%, and 12% of diet DM). Both studies fed steers to a target weight of 650 kg. Differences in composition of feces collected from the rectum and the pen floor of a subset of steers (3 to 7) were examined. Fecal pats from the pen floor of each pen were collected throughout the feeding period and composited by pen. Except for DM, which was higher (P < 0.01) in pen floor than rectal fecal samples, there were minimal differences in fecal constituents between collection methods. In study 1, interactions between grain type and processing index (P ≤ 0.05) were observed, with a reduction in DM, OM, and starch and an increase in NDF and ADL concentrations being associated with more extensively processed wheat than barley. As grain was more extensively processed, ATTD of all nutrients increased (P < 0.01). In study 2, fecal ADF and ADL linearly increased (P < 0.01) with increasing silage in the diet, whereas fecal DM and N linearly decreased (P < 0.01). Digestibility of all nutrients except starch linearly decreased (P < 0.01) with increasing silage. Apparent total tract digestibility of GE predicted using NIRS was related to NEg of the diets as estimated by performance for the wheat-fed steers in study 1 (R² = 0.58, P = 0.03) and those fed increasing silage in study 2 (R² = 0.43, P < 0.01). Similarly, observed ADG could be predicted using NIRS for steers fed wheat in study 1 (R² = 0.48, P = 0.05) and silage in study 2 (R² = 0.40, P < 0.01), but G:F could not. Using NIRS of feces collected from multiple cattle off the feedlot pen floor demonstrated potential for predicting growth performance of finishing cattle. However, grain type and stage of maturity of the cattle impacted the predictability of equations. Increasing the sample size and sampling frequency may be necessary to improve predictions. [ABSTRACT FROM AUTHOR]

The reporting of observational studies in veterinary research presents many challenges that often are not adequately addressed in published reporting guidelines. A consensus meeting of experts was organized to develop an extension of the STROBE statement to address observational studies in veterinary medicine with respect to animal health, animal production, animal welfare and food safety outcomes. The consensus meeting was held 11-13 May 2014 in Mississauga, Ontario, Canada. Seventeen experts from North America, Europe and Australia attended the meeting. The experts were epidemiologists and biostatisticians, many of whom hold or have held editorial positions with relevant journals. Prior to the meeting, 19 experts completed a survey about whether they felt any of the 22 items of the STROBE statement should be modified and whether items should be added to address unique issues related to observational studies in animal species with health, production, welfare or food safety outcomes. At the meeting, the participants were provided with the survey responses and relevant literature concerning the reporting of veterinary observational studies. During the meeting, each STROBE item was discussed to determine whether or not re-wording was recommended, and whether additions were warranted. Anonymous voting was used to determine whether there was consensus for each item change or addition. The consensus was that six items needed no modifications or additions. Modifications or additions were made to the STROBE items numbered as follows: 1 (title and abstract), 3 (objectives), 5 (setting), 6 (participants), 7 (variables), 8 (data sources/measurement), 9 (bias), 10 (study size), 12 (statistical methods), 13 (participants), 14 (descriptive data), 15 (outcome data), 16 (main results), 17 (other analyses), 19 (limitations) and 22 (funding). Published literature was not always available to support modification to, or inclusion of, an item. The methods and processes used in the development of this statement were similar to those used for other extensions of the STROBE statement. The use of this extension to the STROBE statement should improve the reporting of observational studies in veterinary research related to animal health, production, welfare or food safety outcomes by recognizing the unique features of observational studies involving food-producing and companion animals, products of animal origin, aquaculture and wildlife. [ABSTRACT FROM AUTHOR]

The STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) statement was first published in 2007 and again in 2014. The purpose of the original STROBE was to provide guidance for authors, reviewers and editors to improve the comprehensiveness of reporting; however, STROBE has a unique focus on observational studies. Although much of the guidance provided by the original STROBE document is directly applicable, it was deemed useful to map those statements to veterinary concepts, provide veterinary examples and highlight unique aspects of reporting in veterinary observational studies. Here, we present the examples and explanations for the checklist items included in the STROBE-Vet Statement. Thus, this is a companion document to the STROBE-Vet Statement Methods and process document, which describes the checklist and how it was developed. [ABSTRACT FROM AUTHOR]

Background Reporting of observational studies in veterinary research presents challenges that often are not addressed in published reporting guidelines. Objective To develop an extension of the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) statement that addresses unique reporting requirements for observational studies in veterinary medicine related to health, production, welfare, and food safety. Design Consensus meeting of experts. Setting Mississauga, Canada. Participants Seventeen experts from North America, Europe, and Australia. Methods Experts completed a pre-meeting survey about whether items in the STROBE statement should be modified or added to address unique issues related to observational studies in animal species with health, production, welfare, or food safety outcomes. During the meeting, each STROBE item was discussed to determine whether or not rewording was recommended and whether additions were warranted. Anonymous voting was used to determine consensus. Results Six items required no modifications or additions. Modifications or additions were made to the STROBE items 1 (title and abstract), 3 (objectives), 5 (setting), 6 (participants), 7 (variables), 8 (data sources/measurement), 9 (bias), 10 (study size), 12 (statistical methods), 13 (participants), 14 (descriptive data), 15 (outcome data), 16 (main results), 17 (other analyses), 19 (limitations), and 22 (funding). Conclusion The methods and processes used were similar to those used for other extensions of the STROBE statement. The use of this STROBE statement extension should improve reporting of observational studies in veterinary research by recognizing unique features of observational studies involving food-producing and companion animals, products of animal origin, aquaculture, and wildlife. [ABSTRACT FROM AUTHOR]

The STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) statement was first published in 2007 and again in 2014. The purpose of the original STROBE was to provide guidance for authors, reviewers, and editors to improve the comprehensiveness of reporting; however, STROBE has a unique focus on observational studies. Although much of the guidance provided by the original STROBE document is directly applicable, it was deemed useful to map those statements to veterinary concepts, provide veterinary examples, and highlight unique aspects of reporting in veterinary observational studies. Here, we present the examples and explanations for the checklist items included in the STROBE-Vet statement. Thus, this is a companion document to the STROBE-Vet statement methods and process document (JVIM_14575 'Methods and Processes of Developing the Strengthening the Reporting of Observational Studies in Epidemiology-Veterinary (STROBE-Vet) Statement' undergoing proofing), which describes the checklist and how it was developed. [ABSTRACT FROM AUTHOR]

Background: Chronic wasting disease (CWD) is a contagious, fatal prion disease affecting cervids in a growing number of regions across North America. Projected deer population declines and concern about potential spread of CWD to other species warrant strategies to manage this disease. Control efforts to date have been largely unsuccessful, resulting in continuing spread and increasing prevalence. This systematic review summarizes peer-reviewed published reports describing field-applicable CWD control strategies in wild deer populations in North America using systematic review methods. Ten databases were searched for peer-reviewed literature. Following deduplication, relevance screening, full-text appraisal, subject matter expert review and qualitative data extraction, nine references were included describing four distinct management strategies. Results: Six of the nine studies used predictive modeling to evaluate control strategies. All six demonstrated one or more interventions to be effective but results were dependant on parameters and assumptions used in the model. Three found preferential removal of CWD infected deer to be effective in reducing CWD prevalence; one model evaluated a test and slaughter strategy, the other selective removal of infected deer by predators and the third evaluated increased harvest of the sex with highest prevalence (males). Three models evaluated non-selective harvest of deer. There were only three reports that examined primary data collected as part of observational studies. Two of these studies supported the effectiveness of intensive non-selective culling; the third study did not find a difference between areas that were subjected to culling and those that were not. Seven of the nine studies were conducted in the United States. Conclusions: This review highlights the paucity of evaluated, field-applicable control strategies for CWD in wild deer populations. Knowledge gaps in the complex epidemiology of CWD and the intricacies inherent to prion diseases currently pose significant challenges to effective control of this disease in wild deer in North America. [ABSTRACT FROM AUTHOR]

Reasons for performing study Proximal palmar/plantar osteochondral fragmentation of the first phalanx is a frequent radiographic finding in Standardbred horses. These lesions are routinely removed prior to the onset of a racing career with no evidence to support the timing of this surgical intervention. Objectives To determine whether horses racing before surgery slowed as they approached surgery date and whether they speeded up after surgery. To investigate the factors affecting whether a horse raced after surgery and compare the performance of horses that did and did not race before surgery. Study design A retrospective study using 193 Swedish Standardbred trotters. Methods Medical records and radiographs of each horse were examined. Racing data were retrieved from official online records. Generalising estimating equations were used to examine presurgery racing performance and determine whether this differed between horses that raced before surgery and those that had not. Multivariable regression was used to examine career earnings and number of career races. Results Horses racing before surgery neither slowed as they approached surgery, nor speeded up after surgery. Race speed of horses raced before surgery was not different from those that only raced after surgery. Racing before surgery was not associated with whether horses raced following surgery. Only horses with 3 affected legs had slower race speeds than other horses. No other horse level variables affected race speed, number of career races, career earnings or top speed. Conclusions There was no significant difference in race speed between horses that raced before surgery and those that did not. Horses did not slow down prior to surgery. Horses with 3 affected legs ran slower than those with only a single or 2 affected limbs. There was no association between timing of surgery and race speed or career longevity. The potential benefits of surgical intervention should be critically examined. [ABSTRACT FROM AUTHOR]

Circulating immunoglobulin (Ig)G antibodies against M muscarinic acetylcholine receptors (M mAChR) have been implicated in Chagas' disease (ChD) pathophysiology. These antibodies bind to and activate their target receptor, displaying agonist-like activity through an unclear mechanism. This study tested the ability of serum anti-M mAChR antibodies from chronic ChD patients to modulate M muscarinic receptor-receptor interaction by bioluminescence resonance energy transfer (BRET). Human embryonic kidney (HEK) 293 cells co-expressing fusion proteins M mAChR-Renilla luciferase (RLuc) and M mAChR-yellow fluorescent protein (YFP) were exposed to the serum IgG fraction from ChD patients, and BRET between RLuc and YFP was assessed by luminometry. Unlike serum IgG from healthy subjects and conventional muscarinic ligands, ChD IgG promoted a time- and concentration-dependent increase in the BRET signal. This effect neither required cellular integrity nor occurred as a consequence of receptor activation. Enhancement of M receptor-receptor interaction by ChD IgG was receptor subtype-specific and mediated by the recognition of the second extracellular loop of the M mAChR. The monovalent Fab fragment derived from ChD IgG was unable to reproduce the effect of the native immunoglobulin. However, addition of ChD Fab in the presence of anti-human Fab IgG restored BRET-enhancing activity. These data suggest that the modulatory effect of ChD IgG on M receptor-receptor interaction results from receptor cross-linking by bivalent antibodies. [ABSTRACT FROM AUTHOR]

The study objective was to evaluate the accuracy of a real-time polymerase chain reaction (RT-PCR) and a culture protocol used to detect Salmonella in the faeces of grow-finish pigs using a Bayesian approach. The RT-PCR was invA-gene-based assay, while the culture protocol included pre-enrichment in buffered peptone water, selective enrichment in tetrathionate and Rappaport-Vassiliadis broths, and isolation on semi-solid (modified semi-solid RV) or solid (XLT4, Rambach) agar plates. Bayesian analysis was performed using a two-test, two-population model with dependence between culture and RT-PCR and compared to a second model with conditional independence between these two tests. Two hundred and ninety three individual faecal and 294 pooled pen samples from grow-finish pig collected from 10 farms were tested and results were divided into two groups according to herd size (five herds <250 sows, five herds with >400 sows). In the dependence model, RT-PCR sensitivity (Se) and specificity (Sp) were estimated to be 90% (95% probability interval 74, 97) and 99% (98, 99), respectively. Culture Se was 92% (75, 99), while culture Sp was considered 100% as all culture-positive samples were confirmed by serotyping. In the conditional independence model, RT-PCR Se and Sp, and culture Se, were 96% (93, 98), 99% (98, 100) and 97% (94, 100), respectively. The dependence model resulted in posterior estimates of Se that were lower and with broader probability intervals than the independence model, indicating that when RT-PCR and culture are evaluated relative to each other, the correlation between these tests is an important source of bias and should be adjusted for during analysis. The RT-PCR evaluated in this study performed almost comparably to culture; given the cost savings associated with using this test and more timely results, the RT-PCR may be a useful alternative to culture for screening large numbers of samples, particularly when Salmonella prevalence is low. [ABSTRACT FROM AUTHOR]

The accuracy of bacterial culture and PCR for Salmonella in swine was examined through systematic review of existing primary research in this field. A replicable search was conducted in 10 electronic databases. All steps of the review were conducted by two reviewers: to identify relevant publications, to assess their methodological soundness and reporting, and to extract raw data or reported test accuracy estimates. Meta-analyses and meta-regression were performed: to evaluate pooled estimates of test sensitivity (Se) and specificity (Sp), to identify variables explaining the variation in reported test estimates, and to evaluate the association between these variables and reported test Se and Sp. Twenty-nine studies were included in the review. Unique test evaluations reported in these 29 studies were categorized according to the type of test comparison: culture versus culture ( n = 134 test evaluations) and PCR versus culture ( n = 21). We identified significant heterogeneity among evaluations for each test category. For culture, more heterogeneity was caused by differences in individual test protocols (52%) than overall differences between studies (16%). Enrichment temperature, study population, agar and enrichment type were significantly associated with variation in culture Se. Furthermore, interaction between enrichment temperature and enrichment type was detected. For PCR, most of the heterogeneity was caused by overall differences between studies (65-70%); sample type and study size were associated with variation in reported PCR Se and Sp. The overall methodological soundness and/or reporting of primary studies included in this review were poor, with variable use of reference standards, and consistent lack of the use or reporting of blinding, randomization and subject (sample) selection criteria. Consequently, the food safety and veterinary public health research community should formally consider ways for standardizing the conduct and reporting of this type of research. [ABSTRACT FROM AUTHOR]

West Nile virus (WNV) infection in horses was first reported in Canada in 2001 and in the province of Saskatchewan in 2002. This paper outlines the surveillance results of WNV in Saskatchewan horses from 2003 to 2005 and describes the usefulness of its inclusion in an integrated surveillance program in Saskatchewan. The number of human and horse cases was highest in 2003, the epidemic year and then substaintially lower in 2004 and 2005. Horses provided additive information about WNV activity in rural areas with low human population, however, this required willingness and active participation by veterinarians and horse owners. Vaccination impedes the future use of horses in WNV surveillance for public health or veterinary purposes; however, for zoonoses where no vaccination is available, domestic animals would be useful components for surveillance. Integration of surveillance data from human and animal health provide the benefit of a more complex epidemiological picture that can be used to improve public health. [ABSTRACT FROM AUTHOR]

Summary Reasons for performing study: West Nile virus (WNV) was first diagnosed in Saskatchewan equids in 2002. A WNV epidemic was considered highly likely for 2003, which would provide a unique opportunity to study all aspects of WNV subclinical infection and clinical disease development in a relatively naive population. Hypothesis: There are individual equid attributes and management risk factors associated with development of clinical disease. Specifically, this study could address the question of vaccine efficacy for the prevention of development of clinical disease. Methods: A case-control study was conducted in the summer of 2003 during a province-wide outbreak of WNV. Between 5 and 10 equids were sampled from each of 23 case premises with clinical disease and 23 control premises with no apparent or confirmed clinical disease. Data were analysed to identify risk factors for the development of clinical disease. Results: The proportion of equids serologically positive for natural exposure to West Nile virus was 64% (193/300). Nonvaccinated equids were 23 times (95%CI limits 3.0, 168.5, P = 0.002) more likely to develop clinical disease than those vaccinated. The estimate of vaccine efficacy in this field study was 96% (95%CI limits 67%, 99%). Conclusions: The study demonstrated that vaccination was strongly associated with the prevention of clinical disease. Potential relevance: Vaccination is an effective, practical method of prevention of clinical disease. [ABSTRACT FROM AUTHOR]