Effects of a mastitis treatment strategy with or without on-farm testing.

The etiology of mastitis is crucial information to use antimicrobials prudently for control and treatment. This study aimed to evaluate the effects of mastitis diagnosis and treatment strategies with on-farm testing, on cure, new intramammary infections (IMI), somatic cell count (SCC), and antimicrobial use, compared with farmers' current diagnosis and treatment strategies. The on-farm tests used, CHROMagar Mastitis (CHROMagar, Paris, France) and Minnesota Easy Culture System II Tri-plate (University of Minnesota, St. Paul, MN), both had etiological groups of IMI as result, being gram-positive growth, gram-negative growth, or culture negative. Two randomized controlled trials were conducted on 15 herds: trial 1 prospectively enrolled 155 cows with clinical mastitis, and trial 2 cross-sectionally included 78 cows with subclinical mastitis. In both trials, cows were randomly distributed over 3 equal-sized groups: a test group using CHROMagar, a test group using Minnesota, and a control group not using on-farm tests. Farmers decided whether or not to treat, and which antimicrobial treatment would be applied, using information available on the day of enrollment (control group), complemented with the on-farm test result 1 d after enrollment (both test groups). For clinical mastitis, an antimicrobial treatment was given in 58% of cases that used CHROMagar, in 80% that used Minnesota, and in 86% of the controls. For subclinical mastitis, an antimicrobial treatment was given in 50% of cases that used CHROMagar, in 54% that used Minnesota, and in 4% of the controls. Bacteriological cure rate of clinical mastitis was lowest in the CHROMagar group [odds ratio 0.18 (95%CI 0.03-0.99)] compared with the controls. Using the Minnesota on-farm test for subclinical mastitis diagnosis and treatments resulted in fewer new IMI on d 21 [odds ratio 0.06 (95%CI 0.00-0.74)] compared with the controls. Clinical cure rate, percentage of new IMI, and SCC on d 21 of clinical mastitis were comparable among the groups. Using on-farm tests in farmers' decision-making process resulted in more treatments in accordance with the etiology of mastitis than without on-farm testing. A diagnosis and treatment strategy with on-farm testing is advised in cows with clinical mastitis to enhance prudent antimicrobial use. For subclinical mastitis, however, on-farm testing may lead to an unacceptable increase in use of antimicrobials and thus should not be advised as the common approach.

Molecular relatedness of ESBL/AmpC-producing Escherichia coli from humans, animals, food and the environment: a pooled analysis.

Background: In recent years, ESBL/AmpC-producing Escherichia coli (ESBL/AmpC-EC) have been isolated with increasing frequency from animals, food, environmental sources and humans. With incomplete and scattered evidence, the contribution to the human carriage burden from these reservoirs remains unclear. Objectives: To quantify molecular similarities between different reservoirs as a first step towards risk attribution. Methods: Pooled data on ESBL/AmpC-EC isolates were recovered from 35 studies in the Netherlands comprising >27 000 samples, mostly obtained between 2005 and 2015. Frequency distributions of ESBL/AmpC genes from 5808 isolates and replicons of ESBL/AmpC-carrying plasmids from 812 isolates were compared across 22 reservoirs through proportional similarity indices (PSIs) and principal component analyses (PCAs). Results: Predominant ESBL/AmpC genes were identified in each reservoir. PCAs and PSIs revealed close human-animal ESBL/AmpC gene similarity between human farming communities and their animals (broilers and pigs) (PSIs from 0.8 to 0.9). Isolates from people in the general population had higher similarities to those from human clinical settings, surface and sewage water and wild birds (0.7-0.8), while similarities to livestock or food reservoirs were lower (0.3-0.6). Based on rarefaction curves, people in the general population had more diversity in ESBL/AmpC genes and plasmid replicon types than those in other reservoirs. Conclusions: Our 'One Health' approach provides an integrated evaluation of the molecular relatedness of ESBL/AmpC-EC from numerous sources. The analysis showed distinguishable ESBL/AmpC-EC transmission cycles in different hosts and failed to demonstrate a close epidemiological linkage of ESBL/AmpC genes and plasmid replicon types between livestock farms and people in the general population.

Dutch dairy farmers' need for microbiological mastitis diagnostics.

Although several microbiological mastitis diagnostic tools are currently available, dairy farmers rarely use them to base treatment decisions on. In this study, we conducted a telephone interview among 195 randomly selected Dutch dairy farmers to determine their current use of and their need for microbiological diagnostics for clinical mastitis (CM), subclinical mastitis (SCM), and dry-cow treatment (DCT), followed by the test characteristics they consider important. A structured questionnaire was used, based on face-to-face interviews previously held with other farmers. The answers were registered in a database and analyzed using descriptive statistics and univariable and multivariable models. Antimicrobial treatment decisions for CM, SCM, and DCT were mainly based on clinical signs and somatic cell count. In case of CM, 34% of farmers indicated that they currently submit milk samples for bacteriological culture (BC). This would increase to 71% if an on-farm test resulting in treatment advice within 12 h were available. For SCM, use would increase from 22 to 55%, and for DCT, from 7 to 34%, if the same 12-h test were available. For CM and DCT, the preferred test outcome was advice on which antibiotic to use, according to 58 and 15% of the farmers, respectively. For SCM, the preferred test outcome was the causative bacterium for 38% of the farmers. Farmers who currently submit CM milk samples for BC were 13.1 times more likely to indicate, as the preferred test outcome, advice on which antibiotic to use, compared with farmers who do not currently submit CM milk samples for BC. Fourteen percent of the farmers indicated not being interested at all in microbiological mastitis diagnostics for CM. For SCM and DCT, 27 and 55%, respectively, were not interested in microbiological mastitis diagnostics. Regarding test characteristics that farmers considered important, reliability was most often indicated (44-51% of the farmers). Additionally, a preferred time-to-result of ≤8 h for CM and ≤20 to 24 h for SCM and DCT and ≤7% false test outcomes were indicated as desired characteristics of microbiological mastitis diagnostics. Overall, a need seems to exist for microbiological mastitis diagnostic tests among Dutch dairy farmers, specifically for CM, and resulting in a treatment advice. The availability of a reliable diagnostic test, with a suitable time-to-result, will likely increase the use of microbiological mastitis diagnostics and eventually optimize antibiotic usage.

A model for an economically optimal replacement of a breeder flock.

A deterministic model is developed to support the tactical and operational replacement decisions at broiler breeder farms. The marginal net revenue approach is applied to determine the optimal replacement age of a flock. The objective function of the model maximizes the annual gross margin over the flock's production cycle. To calculate the gross margin, future egg production, fertility, or hatchability of the eggs, revenues and variable costs of a flock were estimated. For tactical decisions, the optimal laying length is the age at which the average gross margin of an average flock is maximal. For operational decisions, a flock should be replaced when the marginal gross margin of a replaceable flock is less than the average gross margin of an average flock. To demonstrate the model, a broiler breeder flock from a Dutch breeder farm was used. A sensitivity analysis showed that the optimal replacement decision, for both tactical and operational management, is sensitive to the decrease in the weekly egg production after the peak and the prices of feed and hatching eggs. The effect of the decrease in weekly fertility after the peak on the replacement decision is related to the payment system for hatching eggs.

Prevalence of extended-spectrum and AmpC ß-lactamase-producing Escherichia coli in Dutch dairy herds.

This study was conducted to assess: (1) a change in between-herd prevalence of extended-spectrum and AmpC ß-lactamase-producing Escherichia coli (ESBL/AmpC-EC) between 2011 and 2013, the period during which the antimicrobial policy in animal husbandry in the Netherlands changed significantly, and (2) the prevalence of ESBL/AmpC-EC in individual calves, young stock, and dairy cows in the Netherlands. In 196 randomly selected conventional dairy herds, faecal samples were collected from calves (maximum n = 15), and randomly selected young stock (n = 5) and dairy cows (n = 15). Additionally, fresh faecal samples were collected from five different places on the floors where the dairy cows were housed. Samples were screened for E. coli with non-wild type susceptibility for cefotaxime and isolates were phenotypically confirmed as ESBL/AmpC-producing by disc diffusion, using cefotaxime and ceftazidime with and without clavulanic acid, and cefoxitin. Samples containing ESBL/AmpC-EC were examined semi-quantitatively. In 59.6% of the dairy herds one or more samples tested positive for ESBL/AmpC-EC. The between-herd prevalence based on floor samples in 2013 (18.0%) was significantly lower than the prevalence in 2011 based on comparable samples (32.7%). The individual animal prevalence of ESBL/AmpC-EC, with a minimum shedding level of 103 cfu/g of faeces, was 19.3% in calves, 0.9% in young stock, and 0.8% in dairy cows. Although ESBL/AmpC-EC was found in the majority of dairy herds, the herd prevalence declined significantly between 2011 and 2013. Calves were found to have both, a much higher individual animal prevalence and a higher level of shedding than young stock and cows.

Agreement between four commercial diagnostic tests and routine bacteriological culture of milk to determine the udder infection status of dairy cows.

Mastitis is usually treated based on clinical signs or somatic cell count information rather than on results of bacteriological culture of milk. In many countries an optimal mastitis treatment is considered important from the perspective of therapy efficacy, prudent antimicrobial use and farm economics. Farmers can optimize their mastitis treatment decisions if they know whether and which mastitis pathogen is involved. Information on the mastitis pathogen involved can be acquired from diagnostic mastitis tests such as culture-based tests. This study aimed to determine the agreement of four commercial culture-based mastitis tests with routine bacteriological culture of milk to determine the intramammary infection status of a quarter or cow. The commercial culture-based tests evaluated in this study were CHROMagar Mastitis (CHROMagar, France), Hardy Diagnostics Mastitis Triplate (Hardy Diagnostics, USA), Minnesota Easy Culture System II Tri-plate (University of Minnesota, USA), and VétoRapid (Vetoquinol, the Netherlands). We used 866 prospectively collected milk samples, routinely submitted to the bacteriological laboratory of GD Animal Health for routine bacteriological culture of milk from April to June 2016. Samples were cultured on routine bacteriological culture of milk and on the commercial culture-based tests. We calculated the agreement beyond chance of each commercial culture-based test result with the result of routine bacteriological culture using 2x2 contingency tables. Furthermore, inter-reader agreement was determined for 597 samples read by two masked readers. The agreement of the four commercial culture-based mastitis tests with routine bacteriological culture of milk for Gram-positive bacteria ranged from 0.14 (95% CI 0.11-0.16) using Hardy Diagnostics Mastitis Triplate to 0.25 (95% CI 0.22-0.28) using Minnesota Easy Culture System II Tri-plate. The agreement for Gram-negative bacteria was approximately 0.70 (95% CI 0.66-0.74) for all four commercial culture-based tests. The agreement for no growth ranged from 0.22 (95% CI 0.19-0.25) using Hardy Diagnostics Mastitis Triplate to 0.34 (95% CI 0.31-0.38) using VétoRapid. This category was affected by prevalence and bias as the prevalence adjusted and bias adjusted kappa ranged from 0.63 (95% CI 0.56-0.69) using CHROMagar Mastitis to 0.68 (95% CI 0.62-0.74) using Hardy Diagnostic Mastitis Triplate. Agreement between readers was almost perfect. Although only for Gram-negative bacteria a good agreement was found between commercial culture-based tests and routine bacteriological culture of milk, and further on-farm evaluations are needed to determine the effect of these findings on udder health, commercial culture-based tests are of added value to support decisions whether and how to treat cows with mastitis.

Simulating Escherichia coli O157:H7 transmission to assess effectiveness of interventions in Dutch dairy-beef slaughterhouses.

Beef contamination with Escherichia coli O157:H7 (VTEC) is an important food-safety issue. To investigate the effectiveness of interventions against VTEC in Dutch beef industrial slaughterhouses that slaughter 500 dairy cattle per day, a Monte Carlo simulation model was built. We examined seven carcass-antimicrobial interventions, namely: hot-water wash, lactic-acid rinse, trim, steam-vacuum, steam-pasteurization, hide-wash with ethanol and gamma irradiation, and their combinations. The estimated daily prevalence of contaminated beef-carcass quarters as the output of the model was 9.2%. Contaminated was defined as containing one or more CFU on the surface of a carcass quarter at the end of the quartering stage. Single interventions (except irradiation) could reduce the prevalence to from 6.2% to 1.7%, whereas the combination of interventions could lower it to from 1.2% to 0.1%. The most powerful intervention was irradiation, which could reduce the prevalence to <0.1%. The results of this study indicate that application of single interventions might be useful, although not sufficient. Hence, a combination of interventions along the slaughter process is the more promising approach to reduce the prevalence of contaminated beef quarters.

Costs of rabies control: an economic calculation method applied to Flores Island.

BACKGROUND: Rabies is a zoonotic disease that, in most human cases, is fatal once clinical signs appear. The disease transmits to humans through an animal bite. Dogs are the main vector of rabies in humans on Flores Island, Indonesia, resulting in about 19 human deaths each year. Currently, rabies control measures on Flores Island include mass vaccination and culling of dogs, laboratory diagnostics of suspected rabid dogs, putting imported dogs in quarantine, and pre- and post-exposure treatment (PET) of humans. The objective of this study was to estimate the costs of the applied rabies control measures on Flores Island. METHODOLOGY/PRINCIPAL FINDINGS: A deterministic economic model was developed to calculate the costs of the rabies control measures and their individual cost components from 2000 to 2011. The inputs for the economic model were obtained from (i) relevant literature, (ii) available data on Flores Island, and (iii) experts such as responsible policy makers and veterinarians involved in rabies control measures in the past. As a result, the total costs of rabies control measures were estimated to be US$1.12 million (range: US$0.60-1.47 million) per year. The costs of culling roaming dogs were the highest portion, about 39 percent of the total costs, followed by PET (35 percent), mass vaccination (24 percent), pre-exposure treatment (1.4 percent), and others (1.3 percent) (dog-bite investigation, diagnostic of suspected rabid dogs, trace-back investigation of human contact with rabid dogs, and quarantine of imported dogs). CONCLUSIONS/SIGNIFICANCE: This study demonstrates that rabies has a large economic impact on the government and dog owners. Control of rabies by culling dogs is relatively costly for the dog owners in comparison with other measures. Providing PET for humans is an effective way to prevent rabies, but is costly for government and does not provide a permanent solution to rabies in the future.

Cost analysis of various low pathogenic avian influenza surveillance systems in the Dutch egg layer sector.

BACKGROUND: As low pathogenic avian influenza viruses can mutate into high pathogenic viruses the Dutch poultry sector implemented a surveillance system for low pathogenic avian influenza (LPAI) based on blood samples. It has been suggested that egg yolk samples could be sampled instead of blood samples to survey egg layer farms. To support future decision making about AI surveillance economic criteria are important. Therefore a cost analysis is performed on systems that use either blood or eggs as sampled material. METHODOLOGY/PRINCIPAL FINDINGS: The effectiveness of surveillance using egg or blood samples was evaluated using scenario tree models. Then an economic model was developed that calculates the total costs for eight surveillance systems that have equal effectiveness. The model considers costs for sampling, sample preparation, sample transport, testing, communication of test results and for the confirmation test on false positive results. The surveillance systems varied in sampled material (eggs or blood), sampling location (farm or packing station) and location of sample preparation (laboratory or packing station). It is shown that a hypothetical system in which eggs are sampled at the packing station and samples prepared in a laboratory had the lowest total costs (i.e. € 273,393) a year. Compared to this a hypothetical system in which eggs are sampled at the farm and samples prepared at a laboratory, and the currently implemented system in which blood is sampled at the farm and samples prepared at a laboratory have 6% and 39% higher costs respectively. CONCLUSIONS/SIGNIFICANCE: This study shows that surveillance for avian influenza on egg yolk samples can be done at lower costs than surveillance based on blood samples. The model can be used in future comparison of surveillance systems for different pathogens and hazards.

Financial evaluation of different vaccination strategies for controlling the bluetongue virus serotype 8 epidemic in The Netherlands in 2008.

BACKGROUND: Bluetongue (BT) is a vector-borne disease of ruminants caused by bluetongue virus that is transmitted by biting midges (Culicoides spp.). In 2006, the introduction of BTV serotype 8 (BTV-8) caused a severe epidemic in Western and Central Europe. The principal effective veterinary measure in response to BT was believed to be vaccination accompanied by other measures such as movement restrictions and surveillance. As the number of vaccine doses available at the start of the vaccination campaign was rather uncertain, the Dutch Ministry of Agriculture, Nature and Food Quality and the Dutch agricultural industry wanted to evaluate several different vaccination strategies. This study aimed to rank eight vaccination strategies based on their efficiency (i.e. net costs in relation to prevented losses or benefits) for controlling the bluetongue virus serotype 8 epidemic in 2008. METHODOLOGY/PRINCIPAL FINDINGS: An economic model was developed that included the Dutch professional cattle, sheep and goat sectors together with the hobby farms. Strategies were evaluated based on the least cost - highest benefit frontier, the benefit-cost ratio and the total net returns. Strategy F, where all adult sheep at professional farms in The Netherlands would be vaccinated was very efficient at lowest costs, whereas strategy D, where additional to all adult sheep at professional farms also all adult cattle in the four Northern provinces would be vaccinated, was also very efficient but at a little higher costs. Strategy C, where all adult sheep and cattle at professional farms in the whole of The Netherlands would be vaccinated was also efficient but again at higher costs. CONCLUSIONS/SIGNIFICANCE: This study demonstrates that a financial analysis differentiates between vaccination strategies and indicates important decision rules based on efficiency.

Milk quality assurance for paratuberculosis: simulation of within-herd infection dynamics and economics.

A bulk milk quality assurance programme for Mycobacterium avium subsp. paratuberculosis (Map) in dairy herds was simulated with a stochastic simulation model (JohneSSim). The aim of this study was to evaluate the epidemiological and economic effects of preventive management measures and various test schemes in a simulated population of closed Dutch dairy herds over a 20-year period. Herds were certified as ;low-Map bulk milk' if, with a certain probability, the concentration of Map in bulk milk did not exceed a maximum acceptable concentration of 10(3) Map organisms per litre (based on pasteurisation studies). The programme started with an initial assessment; test-negative herds entered a surveillance procedure and test-positive herds a control procedure. The simulations showed that herd examinations by ELISA for the initial assessment, surveillance and control procedures effectively ensure the quality of ;low-Map bulk milk': > 75% of simulated herds were certified and > 96% of certified herds produced bulk milk with < 10(3) Map/L if the initial herd-level prevalence was 30%. Preventive management measures only had a minor effect on bulk milk quality of certified herds. Culling based on biennial faecal culture was more effective than culling based on annual ELISA. Average total discounted costs for 20-year participation in a programme consisting of initial assessment by ELISA, surveillance by biennial ELISA and control by biennial faecal culture were 16 Euro x 10(3) per herd. In conclusion, this study shows that a bulk milk quality assurance programme for closed Dutch dairy herds is feasible and provides information on the cost-effectiveness of different programmes. The concepts of this study equally apply to other countries because mechanisms of paratuberculosis infection, disease, and testing are comparable in other dairy cattle populations.

Effectiveness of simulated interventions in reducing the estimated prevalence of E. coli O157:H7 in lactating cows in dairy herds.

A transmission model developed to investigate the dynamics of Escherichia coli O157:H7 bacteria in a typical Dutch dairy herd was used to assess the effectiveness of vaccination, diet modification, probiotics (colicin) and hygienic measures as to water troughs and bedding, when they are applied single or in combination, in reducing the prevalence of infected animals. The aim was to rank interventions based on their effectiveness in reducing the baseline prevalence of infected animals in the lactating group. The baseline prevalence of the lactating group and the within-herd prevalence were estimated by the model to be 5.02% and 13.96% respectively. The results show that all four interventions, if applied to all four animal groups or only to young stock, are the most effective and will reduce the baseline prevalence by 84% to 99%. In general, combinations of hygiene (applied in all groups) and one other intervention had the highest effectiveness in reducing prevalence in the lactating group. Vaccination and diet modification show a slightly higher effectiveness than colicin and hygiene.