Impact of Low and High Doses of Marbofloxacin on the Selection of Resistant Enterobacteriaceae in the Commensal Gut Flora of Young Cattle: Discussion of Data from 2 Study Populations.

In the context of requested decrease of antimicrobial use in veterinary medicine, our objective was to assess the impact of two doses of marbofloxacin administered on young bulls (YBs) and veal calves (VCs) treated for bovine respiratory disease, on the total population of Enterobacteriaceae in gut flora and on the emergence of resistant Enterobacteriaceae. In two independent experiments, 48 YBs from 6 commercial farms and 33 VCs previously colostrum deprived and exposed to cefquinome were randomly assigned to one of the three groups LOW, HIGH, and Control. In LOW and HIGH groups, animals received a single injection of, respectively, 2 and 10 mg/kg marbofloxacin. Feces were sampled before treatment, and at several times after treatment. Total and resistant Enterobacteriaceae enumerating were performed by plating dilutions of fecal samples on MacConkey agar plates that were supplemented or not with quinolone. In YBs, marbofloxacin treatment was associated with a transient decrease in total Enterobacteriaceae count between day (D)1 and D3 after treatment. Total Enterobacteriaceae count returned to baseline between D5 and D7 in all groups. None of the 48 YBs harbored marbofloxacin-resistant Enterobacteriaceae before treatment. After treatment, 1 out of 20 YBs from the Control group and 1 out of 14 YBs from the HIGH group exhibited marbofloxacin-resistant Enterobacteriaceae. In VCs, the rate of fluoroquinolone-resistant Enterobacteriaceae significantly increased after low and high doses of marbofloxacin treatment. However, the effect was similar for the two doses, which was probably related to the high level of resistant Enterobacteriaceae exhibited before treatment. Our results suggest that a single treatment with 2 or 10 mg/kg marbofloxacin exerts a moderate selective pressure on commensal Enterobacteriaceae in YBs and in VCs. A fivefold decrease of marbofloxacin regimen did not affect the selection of resistances among commensal bacteria.

Using animal performance data to evidence the under-reporting of case herds during an epizootic: application to an outbreak of bluetongue in cattle.

Following the emergence of the Bluetongue virus serotype 8 (BTV-8) in France in 2006, a surveillance system (both passive and active) was implemented to detect and follow precociously the progression of the epizootic wave. This system did not allow a precise estimation of the extent of the epizootic. Infection by BTV-8 is associated with a decrease of fertility. The objective of this study was to evaluate whether a decrease in fertility can be used to evidence the under-reporting of cases during an epizootic and to quantify to what extent non-reported cases contribute to the total burden of the epizootic. The cow fertility in herds in the outbreak area (reported or not) was monitored around the date of clinical signs. A geostatistical interpolation method was used to estimate a date of clinical signs for non-reported herds. This interpolation was based on the spatiotemporal dynamic of confirmed case herds reported in 2007. Decreases in fertility were evidenced for both types of herds around the date of clinical signs. In non-reported herds, the decrease fertility was large (60% of the effect in reported herds), suggesting that some of these herds have been infected by the virus during 2007. Production losses in non-reported infected herds could thus contribute to an important part of the total burden of the epizootic. Overall, results indicate that performance data can be used to evidence the under-reporting during an epizootic. This approach could be generalized to pathogens that affect cattle's performance, including zoonotic agents such as Coxiella burnetii or Rift Valley fever virus.

How much can diptera-borne viruses persist over unfavourable seasons?

Diptera are vectors of major human and animal pathogens worldwide, such as dengue, West-Nile or bluetongue viruses. In seasonal environments, vector-borne disease occurrence varies with the seasonal variations of vector abundance. We aimed at understanding how diptera-borne viruses can persist for years under seasonal climates while vectors overwinter, which should stop pathogen transmission during winter. Modeling is a relevant integrative approach for investigating the large panel of persistence mechanisms evidenced through experimental and observational studies on specific biological systems. Inter-seasonal persistence of virus may occur in hosts due to viremia duration, chronic infection, or vertical transmission, in vector resistance stages, and due to a low continuous transmission in winter. Using a generic stochastic modeling framework, we determine the parameter ranges under which virus persistence could occur via these different mechanisms. The parameter ranges vary according to the host demographic regime: for a high host population turnover, persistence increases with the mechanism parameter, whereas for a low turnover, persistence is maximal for an optimal range of parameter. Persistence in hosts due to long viremia duration in a few hosts or due to vertical transmission is an effective strategy for the virus to overwinter. Unexpectedly, a low continuous transmission during winter does not give rise to certain persistence, persistence barely occurring for a low turnover of the susceptible population. We propose a generic framework adaptable to most diptera-borne diseases. This framework allows ones to assess the plausibility of each persistence mechanism in real epidemiological situations and to compare the range of parameter values theoretically allowing persistence with the range of values determined experimentally.

Seasonal and spatial heterogeneities in host and vector abundances impact the spatiotemporal spread of bluetongue.

Bluetongue (BT) can cause severe livestock losses and large direct and indirect costs for farmers. To propose targeted control strategies as alternative to massive vaccination, there is a need to better understand how BT virus spread in space and time according to local characteristics of host and vector populations. Our objective was to assess, using a modelling approach, how spatiotemporal heterogeneities in abundance and distribution of hosts and vectors impact the occurrence and amplitude of local and regional BT epidemics. We built a reaction-diffusion model accounting for the seasonality in vector abundance and the active dispersal of vectors. Because of the scale chosen, and movement restrictions imposed during epidemics, host movements and wind-induced passive vector movements were neglected. Four levels of complexity were addressed using a theoretical approach, from a homogeneous to a heterogeneous environment in abundance and distribution of hosts and vectors. These scenarios were illustrated using data on abundance and distribution of hosts and vectors in a real geographical area. We have shown that local epidemics can occur earlier and be larger in scale far from the primary case rather than close to it. Moreover, spatial heterogeneities in hosts and vectors delay the epidemic peak and decrease the infection prevalence. The results obtained on a real area confirmed those obtained on a theoretical domain. Although developed to represent BTV spatiotemporal spread, our model can be used to study other vector-borne diseases of animals with a local to regional spread by vector diffusion.

A reliable severity scoring system for radiographic findings in the limbs of young horses.

The validity of methods used to score the severity of radiographic findings (RFs) in horses is uncertain since only one or two joints are usually studied, classification criteria are heterogeneous and the internal validity is not assessed. The aim of this study was to assess the internal validity of a severity scoring system (SSS) of RFs by repeated scoring of a sample of radiographs. This SSS of RFs is based on four criteria that can be applied to every type of RF observed in limb joints. It consists of five weighted severity indexes (0, 1, 2, 4, 8) and was used to assess RFs found on the limbs of 392 young horses. The internal validity of the SSS was assessed using Kappa coefficients calculated on a subsample of 137 horses whose radiographs were interpreted twice. The final RF severity indices from these radiographs were obtained after three experienced veterinarians had reached a consensus, similar to the procedure used at foal and yearling sales. The majority of RFs from the 392 horses were scored either 1 or 2, while scores of 8 were only observed in the stifle and tarsus. Among the subsample, the overall agreement on the presence or absence of RFs was good (κ=0.63; 95% Confidence Interval [CI], 0.56-0.69), and was excellent for the severity of RFs (weighted κ=0.82; 95% CI, 0.75-0.87). Most disagreements involved RFs that scored 1. The fore fetlock and the carpus experienced the lowest agreement. The SSS was a stable and reliable procedure applicable to any RF on any limb joint of the horse. It will be of potential interest in clinical practice and in the pre-purchase evaluation of young horses and could also be used in additional studies on the evolution or risk factors of RFs.

Association of growth, feeding practices and exercise conditions with the severity of the osteoarticular status of limbs in French foals.

The aim of this study was to identify the risk factors for the severity of Juvenile OsteoChondral Conditions (JOCC) in limbs of French foals. Twenty-one farms in Normandy, France, were sampled and enrolled in a cohort study including 378 foals from three breeds, followed from the 8th month of pregnancy of the mares until the foals were approximately 6months old. Data on growth, feeding practices and exercise conditions were regularly collected. The carpus, the front and hind digits, the hock and the stifle of the foals were radiographed at the end of follow-up. JOCC severity in each foal was described using a global appraisal of its osteoarticular status (OAS) depending on the number and the severity of radiographic findings. Of the 378 foals, 53% had a good OAS, 34% had an intermediate OAS and 13% had a poor OAS. The breed (Selle Français and French Trotter Standardbred vs. Thoroughbred), a high girth perimeter at early age and an irregular exercise were significantly associated with a poor OAS. This study contributes to the understanding of the development of JOCC. An increased growth and reduced or irregular physical activity during the first weeks of life would be responsible for more severe lesions. Growth and exercise conditions should be carefully monitored to reduce the prevalence of severe JOCC in foals.

Transmission dynamics of Mycoplasma bovis in newly received beef bulls at fattening operations.

Mycoplasma bovis is an important cause of bovine respiratory disease (BRD) in newly received cattle at fattening operations. However, little information on its within-pen transmission dynamics during a BRD outbreak is available. Such information is nevertheless crucial to adapt control measures during M. bovis-associated BRD outbreaks. The objective of the current study was to determine whether single or multiple clones of M. bovis are present within a pen during a BRD outbreak that occurs early in the feeding period. Sixteen BRD outbreaks that naturally occurred in 12 pens of 8-12 bulls each (n = 112) newly received at 3 fattening operations were investigated. Two hundred and thirty-nine transtracheal aspirations (TTA) were performed during the outbreaks, and the M. bovis isolates obtained were characterized by pulsed-field gel electrophoresis (PFGE). Mycoplasma bovis isolates were recovered from TTA in 8 of the 16 BRD outbreaks that occurred. The within-pen prevalence of bulls positive for M. bovis during these outbreaks ranged from 8% to 100%. The PFGE analysis revealed that, even though bulls came from multiple origins, a single clone of M. bovis was present within a pen during BRD outbreaks with a high prevalence of M. bovis infection. The study therefore indicates that, even if M. bovis can recrudesce from carriers after stressful events such as transportation and commingling, the increased prevalence of M. bovis pulmonary infection observed during BRD outbreaks that are early occurring in the feeding period seems primarily due to the horizontal transmission of only 1 clone among cattle.

Seasonal spread and control of Bluetongue in cattle.

Bluetongue is a seasonal midge-borne disease of ruminants with economic consequences on herd productivity and animal trade. Recently, two new modes of transmission have been demonstrated in cattle for Bluetongue virus serotype 8 (BTV8): vertical and pseudo-vertical transmission. Our objective was to model the seasonal spread of BTV8 over several years in a homogeneous population of cattle, and to evaluate the effectiveness of vaccination strategies. We built a deterministic mathematical model accounting for the seasonality in vector abundance and all the modes of transmission. We proposed a counterpart of the basic reproduction number (R(0)) in a seasonal context (R(S)). Set A(t) is the number of secondary cases produced by a primary case introduced at time t. R(S) is the average of A(t). It is a function of midge abundance and vaccination strategy. We also used A*, the maximum of A(t), as an indicator of the risk of an epidemic. Without vaccination, the model predicted a large first epidemic peak followed by smaller annual peaks if R(S)>1. When R(S)<1, small epidemics could occur if A* >1. Vaccination reduced R(S) and A* to less than one, but almost perfect vaccine efficacy and coverage were required to ensure no epidemics occurred. However, a lower coverage resulting in R(S)>1 could decrease infection prevalence. A further step would be to optimize vaccination strategies by targeting an appropriate period of the year to implement the vaccination.

Genetic instability of Campylobacter coli in the digestive tract of experimentally infected pigs.

Campylobacter, a leading cause of food-borne illness worldwide, has a widespread distribution with a broad range of animal hosts and environmental reservoirs. The genetic description of bacterial strains is a powerful tool for epidemiological studies but can be impaired by the high genomic variability of Campylobacter. Our study aimed (i) at investigating the genotypic instability of Campylobacter generated either in vitro by subculturing or after in vivo passage on specific pathogen-free pigs and (ii) at evaluating the suitability of typing methods to detect such variation. Pigs were inoculated per os with three Campylobacter strains (one C. coli originating from pig faeces, one C. jejuni and one C. coli originating from poultry faeces) alone or in mixture and non-inoculated pigs were housed in adjacent pens. Genotypic instability was investigated using both macrorestriction combined with pulsed-field gel electrophoresis analysis (PFGE) and PCR restriction fragment length polymorphism analysis of the flaA gene (flaA PCR-RFLP). No variability in the genetic profile was observed for the three strains maintained through twenty times subculturing events in vitro. Genotypic variability was evidenced in vivo only in pigs inoculated with C. coli of porcine origin, either alone or in a mix, with both genotyping methods. In our study, for one porcine C. coli strain, 13% and 21% of variability were generated in the digestive tract of pigs by PFGE and flaA PCR-RFLP typing methods, respectively. This study is a first approach for a better understanding of the genomic instability of Campylobacter in pig under field conditions.

A side effect of decreased fertility associated with vaccination against bluetongue virus serotype 8 in Holstein dairy cows.

Inactivated virus vaccines have been widely used to control bluetongue after introduction of serotype 8 of the bluetongue virus (BTV) in northern Europe in 2006. To evaluate vaccination, quantitative knowledge of its possible side effects is needed. One current adverse reaction with inactivated vaccines is a rise in body temperature, which could reduce cow reproductive performance. The objective of this study was to quantify a possible side effect of vaccination on fertility before the implantation of the embryo of dairy cows under field conditions. The study was performed on herds that were not exposed to BTV. Fertility was assessed by return-to-service following artificial insemination (AI). Biological assumptions for a possible side effect of vaccination were conception failure and embryonic death. Associations between return-to-service rates and vaccine injections were assessed using mixed-logistic regression models and survival analysis. Two models were considered: a 3-week-return-to-service model comparing cows vaccinated between 3 days before and 16 days after AI and unvaccinated cows (assuming an effect on conception failure or early embryonic death), and a 90-day-return-to-service model comparing cows vaccinated between 3 days before and 42 days after AI and unvaccinated cows (assuming an effect on conception failure, early or late embryonic death). Only cows receiving a second vaccine injection between 2 and 7 days after AI had a significantly higher risk of 3-week-return-to-service (RR=1.19 [1.07-1.33]). This corresponds to an increase of return-to-service by 4 percentage points. A side effect of vaccination could be due to early embryonic death. The slight side effect on fertility associated with vaccination was low compared to effects of BTV-8 exposure on fertility.

Seroprevalence of Q fever in naturally infected dairy cattle herds.

Coxiella burnetii is the causal agent of Q fever, a worldwide spread zoonosis. Prevention of C. burnetii shedding in cattle is critical to control the spread of the pathogen between animals, and from animals to humans. Vaccination with a phase 1 vaccine has been shown to be effective in preventing shedding when implemented in still susceptible animals, even in infected cattle herds. The identification of these animals (dairy cows and nulliparous females) as targets for vaccination consequently is crucial. Hygiene measures conventionally also are implemented, but their relative impact on C. burnetii diffusion remains unknown. The objectives of this study therefore were to (i) describe the distribution of the within-herd apparent seroprevalence among cows and nulliparous females and (ii) to explore the association between management practices and herd characteristics on the one hand, and these seroprevalences on the other. In a sample of 100 naturally and clinically infected dairy herds, blood samples were taken systematically from all nulliparous females (older than 12 months) and cows, and serologically tested. Information on herd characteristics and management practices were collected through a questionnaire filled in by each farmer. The variation in within-herd seroprevalence among cows and the risk for a herd of having at least one seropositive nulliparous female were investigated using multivariate (linear and logistic respectively) regression models. Median within-herd seroprevalence was 0.32 (Q1=0.22; Q3=0.43). We observed a low to null (median=0.01; Q1=0; Q3=0.10) within-herd seroprevalence in nulliparous females contrary to a high value (median=0.42) and variability (Q1=0.28; Q3=0.56) in cows. Only a few herd characteristics and management practices were found to be related to seroprevalence. Within-herd seroprevalence in cows was found to be significantly (P<0.10) higher in herds (i) with a number of cows<46, (ii) with seasonal calving, and (iii) with grazing or contact through the fence with other ruminant herds. The risk of having at least one seropositive nulliparous female was increased in herds (i) with seasonal calving and (ii) where the foetus and/or the placenta of aborted cows were not systematically removed. Our findings support, in addition to the implementation of high level of hygiene measures, the relevance of vaccination (at least in nulliparous females) as a method to control the spread of C. burnetii within an infected herd, as vaccination is effective in susceptible animals and given that nulliparous females are mostly not infected even in infected herds.

Rapid identification and quantification of Campylobacter coli and Campylobacter jejuni by real-time PCR in pure cultures and in complex samples.

BACKGROUND: Campylobacter spp., especially Campylobacter jejuni (C. jejuni) and Campylobacter coli (C. coli), are recognized as the leading human foodborne pathogens in developed countries. Livestock animals carrying Campylobacter pose an important risk for human contamination. Pigs are known to be frequently colonized with Campylobacter, especially C. coli, and to excrete high numbers of this pathogen in their faeces. Molecular tools, notably real-time PCR, provide an effective, rapid, and sensitive alternative to culture-based methods for the detection of C. coli and C. jejuni in various substrates. In order to serve as a diagnostic tool supporting Campylobacter epidemiology, we developed a quantitative real-time PCR method for species-specific detection and quantification of C. coli and C. jejuni directly in faecal, feed, and environmental samples. RESULTS: With a sensitivity of 10 genome copies and a linear range of seven to eight orders of magnitude, the C. coli and C. jejuni real-time PCR assays allowed a precise quantification of purified DNA from C. coli and C. jejuni. The assays were highly specific and showed a 6-log-linear dynamic range of quantification with a quantitative detection limit of approximately 2.5 × 10² CFU/g of faeces, 1.3 × 10² CFU/g of feed, and 1.0 × 10³ CFU/m² for the environmental samples. Compared to the results obtained by culture, both C. coli and C. jejuni real-time PCR assays exhibited a specificity of 96.2% with a kappa of 0.94 and 0.89 respectively. For faecal samples of experimentally infected pigs, the coefficients of correlation between the C. coli or C. jejuni real-time PCR assay and culture enumeration were R² = 0.90 and R² = 0.93 respectively. CONCLUSION: The C. coli and C. jejuni real-time quantitative PCR assays developed in this study provide a method capable of directly detecting and quantifying C. coli and C. jejuni in faeces, feed, and environmental samples. These assays represent a new diagnostic tool for studying the epidemiology of Campylobacter by, for instance, investigating the carriage and excretion of C. coli and C. jejuni by pigs from conventional herds.

Predicting fadeout versus persistence of paratuberculosis in a dairy cattle herd for management and control purposes: a modelling study.

Epidemiological models enable to better understand the dynamics of infectious diseases and to assess ex-ante control strategies. For Mycobacterium avium subsp. paratuberculosis (Map), possible transmission routes have been described, but Map spread in a herd and the relative importance of the routes are currently insufficiently understood to prioritize control measures. We aim to predict early after Map introduction in a dairy cattle herd whether infection is likely to fade out or persist, when no control measures are implemented, using a modelling approach. Both vertical transmission and horizontal transmission via the ingestion of colostrum, milk, or faeces present in the contaminated environment were modelled. Calf-to-calf indirect transmission was possible. Six health states were represented: susceptible, transiently infectious, latently infected, subclinically infected, clinically affected, and resistant. The model was partially validated by comparing the simulated prevalence with field data. Housing facilities and contacts between animals were specifically considered for calves and heifers. After the introduction of one infected animal in a naive herd, fadeout occurred in 66% of the runs. When Map persisted, the prevalence of infected animals increased to 88% in 25 years. The two main transmission routes were via the farm's environment and in utero transmission. Calf-to-calf transmission was minor. Fadeout versus Map persistence could be differentiated with the number of clinically affected animals, which was rarely above one when fadeout occurred. Therefore, early detection of affected animals is crucial in preventing Map persistence in dairy herds.

Quantification of Campylobacter spp. in pig feces by direct real-time PCR with an internal control of extraction and amplification.

The rapid and direct quantification of Campylobacter spp. in complex substrates like feces or environmental samples is crucial to facilitate epidemiological studies on Campylobacter in pig production systems. We developed a real-time PCR assay for detecting and quantifying Campylobacter spp. directly in pig feces with the use of an internal control. Campylobacter spp. and Yersinia ruckeri primers-probes sets were designed and checked for specificity with diverse Campylobacter, related organisms, and other bacterial pathogens before being used in field samples. The quantification of Campylobacter spp. by the real-time PCR then was realized on 531 fecal samples obtained from experimentally and naturally infected pigs; the numeration of Campylobacter on Karmali plate was done in parallel. Yersinia ruckeri, used as bacterial internal control, was added to the samples before DNA extraction to control DNA-extraction and PCR-amplification. The sensitivity of the PCR assay was 10 genome copies. The established Campylobacter real-time PCR assay showed a 7-log-wide linear dynamic range of quantification (R²=0.99) with a detection limit of 200 Colony Forming Units of Campylobacter per gram of feces. A high correlation was found between the results obtained by real-time PCR and those by culture at both qualitative and quantitative levels. Moreover, DNA extraction followed by real-time PCR reduced the time needed for analysis to a few hours (within a working day). In conclusion, the real-time PCR developed in this study provides new tools for further epidemiological surveys to investigate the carriage and excretion of Campylobacter by pigs.

Early detection of bovine respiratory disease in young bulls using reticulo-rumen temperature boluses.

The use of reticulo-rumen temperature boluses to detect bovine respiratory disease (BRD) was investigated in young bulls following their entry into a fattening unit. Twenty-four bulls received a bolus at entry and were observed for 40 days. As soon as a reticulo-rumen hyperthermia (RH) episode was detected using the bolus, clinical examination was performed by a veterinarian and then repeated every 12-24h until the end of RH episode. Fifty-two RH episodes were detected in 22 animals. High rectal temperatures (40.1±0.6°C) were observed during these episodes. BRD was diagnosed on the basis of clinical examination during 38/52 RH episodes in 21 animals (positive predictive value 73%). The onset of BRD signs always occurred after the onset of RH episodes, with a time-lag from 12 to 136 h, depending on BRD signs. Monitoring reticulo-rumen temperature permits early detection of BRD; however, clinical examination is required to confirm BRD.

Prevalence of Coxiella burnetii infection in domestic ruminants: a critical review.

Reliable detection of Coxiella burnetii is a critical point for the control of the spread of this zoonotic disease (Q fever), ruminants being considered as the main source for human infection as confirmed by the recent human outbreak in the Netherlands since 2007. Considering both public and animal health, providing consolidated prevalence data could be relevant within the decision process of public policy makers or producers organizations. The objective of this study was to conduct a critical review of the literature focused on the prevalence of C. burnetii infection at animal, herd and within-herd levels in cattle, goat and sheep. A qualitative assessment of the 69 selected publications, based on the analysis of the sampling frame and testing procedures, was also performed. While the number of publications increased recently, major methodological issues were still evidenced. These critical issues were related to (i) the absence of description of the sampling strategy and (ii) the lack of sensitivity of the testing procedure. The lack of well designed studies makes not possible to estimate accurately the current prevalence of the infection. Nevertheless, the literature review reported the detection of C. burnetii infection in the all 5 continents with a wide range whatever the species. The apparent prevalence was slightly higher in cattle (20.0% and 37.7% of mean apparent prevalence at animal and herd level respectively) than in small ruminants (around 15.0% and 25% respectively for animal and herd level in sheep and goat). The present conclusions and the current situation support the persistent need of conducting well designed studies, aiming at estimating the true prevalence of C. burnetii infection in the three main domestic ruminant species.

Evaluation of a commercial real-time reverse transcription polymerase chain reaction kit for the diagnosis of Bovine respiratory syncytial virus infection.

Recently a commercial real-time reverse transcription polymerase chain reaction (RT-PCR) kit has been marketed for the detection of Bovine respiratory syncytial virus (BRSV). However, diagnostic interpretation of the results of this kit requires its comparison to commonly used methods. Therefore, the objective of this study was to evaluate the performance of this kit in comparison with the conventional direct fluorescent antibody test (FAT). Twenty BRSV strains and 14 heterologous bovine viruses were used to check the kit's sensitivity and specificity. The efficiency and detection limit of the kit were determined by testing dilution series of a BRSV strain. The comparison between real-time RT-PCR kit and FAT was performed with 94 clinical samples from calves with clinical signs of respiratory disease including lung tissues (n = 55), transtracheal aspiration samples (n = 20), and nasal swab samples (n = 19). All of the BRSV strains tested were detected by real-time RT-PCR. No cross-reaction was shown with the 14 heterologous bovine viruses. The real-time RT-PCR was 99.3% efficient with a detection limit of 0.1 TCID(50) (50% tissue culture infective dose). The results of real-time RT-PCR and FAT were concordant for 65 of the 94 clinical samples tested. The remaining 29 clinical samples were positive by real-time RT-PCR and negative by FAT, demonstrating the higher sensitivity of real-time RT-PCR. In conclusion, the kit evaluated in this study was sensitive, specific, and had a low threshold of detection. Furthermore, the use of this kit instead of FAT allows an improvement of the sensitivity for the detection of BRSV in clinical samples.

Management- and housing-related risk factors of respiratory disorders in non-weaned French Charolais calves.

Our aim was to determine at calf-batch level the management- and housing-related risk factors of respiratory disorders in non-weaned Charolais calves. Farmers recorded cases according to the definition provided i.e. the association of at least one respiratory sign and, in the same calf or another calf of the same batch, at least one general sign on the same day or the day before. During farm visits, quality of farmers' records was checked and questionnaires were applied to gather farm and herd characteristics and to describe farming practices and housing facilities. Data were suitable for analysis for 172 batches where no metaphylactic treatment was implemented. Batches had great disparity in incidence of respiratory disorders. In the 120 batches with at least one case, the quartiles of incidence rate were, respectively, 0.95, 2.15 and 3.59 cases per 1000 calf-days at-risk. For risk-factor analysis, the statistical unit was the calf-batch located in a given batch. We used a ZINB model because (i) there was significant overdispersion of incidence rates of respiratory disorders (overdispersion test statistic of O=1049 (P<0.001)), (ii) probability was high that a two-group modelling process existed (Vuong statistic of V=2.44 (P=0.0073)) and (iii) the ZINB model fit significantly better than the ZIP model (likelihood-ratio statistic of 340.14 (P<0.001)). The risk was higher in open-fronted barns or in open barns compared to closed ones (incidence-rate ratios (IRRs): 1.9 and 1.8), in barns where no annual disinfection was implemented (IRR: 1.5) and in part slope with straw/part scraped and in part straw-bedded/part scraped barns compared to completely straw-bedded barns (IRRs: 1.9 and 1.6). Larger calf-batches were more at-risk than smaller batches (OR for the effect of an increase of 10 calves on the probability of a 0 count: 0.5).

A case-based learning approach for teaching undergraduate veterinary students about dairy herd health consultancy issues.

A case-based learning (CBL) format was implemented at the Veterinary School of Nantes, France, for veterinary students in their last year of the curriculum who had chosen to track toward a farm animal career. The focus of the CBL format was learning about dairy herd health consultancy. The goal was to emphasize teamwork among students, introduce professional communications and advisory relationships with clients, and work within the technical and economic limitations of participating farms. These farms volunteered to participate and had identified a problem. The learning objectives included gaining basic knowledge of herd-level diseases and the methods to control these within herds. The program focused on health audits of dairy farms performed by teams of four to five students, culminating in submission of a herd health management action plan specific for the farm visited by each team. The CBL program was comprised of defined learning objectives for each team. The learning process was supervised, from orientation through to validation, by a panel of experts from within the veterinary school and from local industry. Teams submitted written reports that listed recommendations and an action plan for implementation. This report was defended by each team in front of the farmers, their professional partners, and the panel of supervisors. Assessment of the program by students, participating farms, and industry professionals was positive.

Prevention of Coxiella burnetii shedding in infected dairy herds using a phase I C. burnetii inactivated vaccine.

The main objective of this study was to assess the efficacy of a monovalent inactivated vaccine containing phase I Coxiella burnetii to prevent Coxiella shedding in susceptible dairy cows within infected herds in comparison to a placebo. A total of 336 dairy cows and heifers, from six spontaneously infected herds, were followed over a 1-year period. Before treatment (i.e. vaccination or placebo), the C. burnetii infection status of the cows was determined on the basis on PCR results on milk, vaginal mucus and faeces and serological analysis performed 2 weeks apart. A cow was considered susceptible (i.e. non-infected) when all results were negative, and was considered infected otherwise. The allocation of treatments was performed randomly within pregnant and non-pregnant cows. After treatment (D0), the animals were subject to systematic sampling (milk, vaginal mucus and faeces) on D90, D180, D270 and D360 to detect putative shedding. In addition, the same samples were taken within 15 days after calving. An animal was considered as a shedder at a given time t, if at t, it was found PCR-positive on at least one test taken among the samples (milk, vaginal mucus and faeces). The effect of the treatment on the probability for an initially susceptible animal of becoming shedder was assessed using survival analysis techniques (Cox regression model). Almost all heifers were detected as susceptible before treatment. When vaccinated while not pregnant, an animal had a five times lower probability of becoming a shedder than an animal receiving placebo. An animal which was vaccinated while pregnant had a similar probability of becoming shedder as an animal receiving the placebo. There was no significant farm effect in this multi-centric trial. These results highlight the value of implementing vaccination, if possible, in non-infected herds. In infected herds, the vaccination should be implemented in quite all presumably susceptible animals, i.e. at least the heifers. The vaccination of the dairy cows should be performed when the within-herd seroprevalence is low, i.e. in herds where the infection has not spread widely yet.