Bart H.P. van den Borne

Mycoplasma bovis infections in Swiss dairy cattle: a clinical investigation

Mycoplasma bovis causes mastitis in dairy cows and is associated with pneumonia and polyarthritis in cattle. The present investigation included a retrospective case–control study to identify potential herd-level risk factors for M. bovis associated disease, and a prospective cohort study to evaluate the course of clinical disease in M. bovis infected dairy cattle herds in Switzerland. Eighteen herds with confirmed M. bovis cases were visited twice within an average interval of 75 d. One control herd with no history of clinical mycoplasmosis, matched for herd size, was randomly selected within a 10 km range for each case herd. Animal health data, production data, information on milking and feeding-management, housing and presence of potential stress- factors were collected. Composite quarter milk samples were aseptically collected from all lactating cows and 5% of all animals within each herd were sampled by nasal swabs. Organ samples of culled diseased cows were collected when logistically possible. All samples were analyzed by real-time polymerase chain reaction (PCR). In case herds, incidence risk of pneumonia, arthritis and clinical mastitis prior to the first visit and incidence rates of clinical mastitis and clinical pneumonia between the two visits was estimated. Logistic regression was used to identify potential herd-level risk factors for M. bovis infection. In case herds, incidence risk of M. bovis mastitis prior to the first visit ranged from 2 to 15%, whereas 2 to 35% of the cows suffered from clinical pneumonia within the 12 months prior to the first herd visit. The incidence rates of mycoplasmal mastitis and clinical pneumonia between the two herd visits were low in case herds (0–0.1 per animal year at risk and 0.1-0.6 per animal year at risk, respectively). In the retrospective-case-control study high mean milk production, appropriate stimulation until milk-let-down, fore-stripping, animal movements (cattle shows and trade), presence of stress-factors, and use of a specific brand of milking equipment, were identified as potential herd-level risk factors. The prospective cohort study revealed a decreased incidence of clinical disease within three months and prolonged colonization of the nasal cavity by M. bovis in young stock.

Epidemiologic survey in Swiss group-housed breeding rabbits: extent of lesions and potential risk factors.

In Switzerland, group-housing for breeding rabbit does is not explicitly required by law, but label programmes, as well as the general public and animal welfare groups, are advocating it. Although group-housing is of great benefit to the gregariously living rabbits, the establishment of a social hierarchy within the group might lead to stress and lesions. In the present epidemiological study, lesions were scored twice on 30% of the breeding does on all 28 commercial Swiss farms with group-housed breeding does. Additionally, a detailed questionnaire was filled out with all producers to determine risk factors potentially associated with lesions. Data were analysed using hierarchical proportional odds models. About 33% of the does examined had lesions, including wounds that were almost healed and small scratches. Severe lesions were counted on 9% of the animals. Differences between seasons in lesions score were identified, with the extent of lesions being higher in summer than in spring. Fewer lesions occurred on farms on which mastitis was more common. More lesions were found on farms where the does were isolated between littering and artificial insemination than on farms without isolation. According to the producers, most of the aggression occurred directly after the isolation phase when the does were regrouped again. We conclude that lesions in group-housed breeding does might be reduced by appropriate reproductive management.

Questionnaire-based study to assess the association between management practices and mastitis within tie-stall and free-stall dairy housing systems in Switzerland

BackgroundProphylactic measures are key components of dairy herd mastitis control programs, but some are only relevant in specific housing systems. To assess the association between management practices and mastitis incidence, data collected in 2011 by a survey among 979 randomly selected Swiss dairy farms, and information from the regular test day recordings from 680 of these farms was analyzed.ResultsThe median incidence of farmer-reported clinical mastitis (ICM) was 11.6 (mean 14.7) cases per 100 cows per year. The median annual proportion of milk samples with a composite somatic cell count (PSCC) above 200,000 cells/ml was 16.1 (mean 17.3) %. A multivariable negative binomial regression model was fitted for each of the mastitis indicators for farms with tie-stall and free-stall housing systems separately to study the effect of other (than housing system) management practices on the ICM and PSCC events (above 200,000 cells/ml). The results differed substantially by housing system and outcome. In tie-stall systems, clinical mastitis incidence was mainly affected by region (mountainous production zone; incidence rate ratio (IRR) = 0.73), the dairy herd replacement system (1.27) and farmers age (0.81). The proportion of high SCC was mainly associated with dry cow udder controls (IRR = 0.67), clean bedding material at calving (IRR = 1.72), using total merit values to select bulls (IRR = 1.57) and body condition scoring (IRR = 0.74). In free-stall systems, the IRR for clinical mastitis was mainly associated with stall climate/temperature (IRR = 1.65), comfort mats as resting surface (IRR = 0.75) and when no feed analysis was carried out (IRR = 1.18). The proportion of high SSC was only associated with hand and arm cleaning after calving (IRR = 0.81) and beef producing value to select bulls (IRR = 0.66).ConclusionsThere were substantial differences in identified risk factors in the four models. Some of the factors were in agreement with the reported literature while others were not. This highlights the multifactorial nature of the disease and the differences in the risks for both mastitis manifestations. Attempting to understand these multifactorial associations for mastitis within larger management groups continues to play an important role in mastitis control programs.

A longitudinal study on transmission of Staphylococcus aureus genotype B in Swiss communal dairy herds

Staphylococcus aureus is a common mastitis causing pathogen of dairy cattle. Several S. aureus genotypes exist, of which genotype B (GTB) is highly prevalent in Swiss dairy herds. Dairy farming in mountainous regions of Switzerland is characterised by the movement of dairy cattle to communal pasture-based operations at higher altitudes. Cows from different herds of origin share pastures and milking equipment for a period of 2 to 3 months during summer. The aim of this longitudinal observational study was to quantify transmission of S. aureus GTB in communal dairy operations. Cows (n=551) belonging to 7 communal operations were sampled at the beginning and end of the communal period. Transmission parameter β was estimated using a Susceptible-Infectious-Susceptible (SIS) model. The basic reproduction ratio R0 was subsequently derived using previously published information about the duration of infection. Mean transmission parameter β was estimated to be 0.0232 (95% CI: 0.0197-0.0274). R0 was 2.6 (95% CI: 2.2-3.0), indicating that S. aureus GTB is capable of causing major outbreaks in Swiss communal dairy operations. This study emphasized the contagious behaviour of S. aureus GTB. Mastitis management in communal dairy operations should be optimized to reduce S. aureus GTB transmission between cows and back to their herds of origin.

Quantifying Preferences of Farmers and Veterinarians for National Animal Health Programs: The Example of Bovine Mastitis and Antimicrobial Usage in Switzerland

Bovine udder health in Switzerland is of a relatively high level. However, antimicrobial usage (AMU) seems high in comparison to other European countries also. A new udder health and AMU improvement program could improve this situation but it is uncertain whether there is support from the field. This study aimed to quantify preferences of dairy farmers and veterinarians for the start and design characteristics of a new national udder health and AMU improvement program in Switzerland. A total of 478 dairy farmers and 98 veterinarians completed an online questionnaire. Questions on their demographics and their mindset toward AMU were complemented with an adaptive choice-based conjoint interview, a novel conjoint analysis technique to quantify preferences of respondents for characteristics of a product for which multiple trade-off decisions must be made (here a bovine udder health and AMU improvement program). The conjoint analysis was followed by a multivariate multiple regression analysis to identify groups of respondents with different program design preferences. Logistic regression models were used to associate covariates with respondents’ preference to start a new udder health and AMU improvement program. Most farmers (55%) and veterinarians (62%) were in favor of starting a new voluntary udder health and AMU improvement program, but the program design preferences agreed moderately between the two stakeholder groups. Farmers preferred an udder health and AMU improvement program that did not contain a penalty system for high AMU, was voluntary for all dairy herds, and aimed to simultaneously improve udder health and reduce AMU. Veterinarians preferred a program that had the veterinary organization and the government taking the lead in program design decision making, did not contain a penalty system for high AMU, and aimed to simultaneously improve udder health and reduce AMU. Differences between groups of farmers and veterinarians concerning their start preference were identified. Also, the magnitude of various program design preferences changed for farmers with different opinions toward AMU. The information obtained from this study may support the decision-making process and the communication to the field afterward, when discussing national strategies to improve udder health and AMU in Switzerland.

SVEPM 2017-Recent developments and contemporary foci in veterinary epidemiology and economics, Society of Veterinary Epidemiology and Preventive Medicine conference Inverness, Scotland 29-31 March 2017

The 2017 Annual Meeting of the Society for Veterinary Epidemiology and Preventive Medicine (SVEPM), held in Inverness, Scotland, highlighted recent developments and contemporary foci in veterinary epidemiology and economics. Workshops included: aquaculture and epidemiology; risk assessment of vector-borne diseases; reporting guidelines for observational studies; systems thinking for disease management; techniques to teach epidemiology; and infectious disease modelling with SimInf. From within the conference programme, the five papers contained in this Special Issue of Preventive Veterinary Medicine demonstrate the excellent platform for networking between veterinary epidemiologists, public health professionals, economists and aligned professionals which this conference provides. Topics include the use of stochastic simulation modelling to investigate the efficacy of risk mitigating scenarios to maintain disease free status for Infectious Bovine Rhinotracheitis (IBR), budgetary and implementation impacts of changing control strategy from mandatory towards indirect testing for Bovine Viral Diarrhoea (BVD), the effects of imperfect testing regimes upon disease frequency and association with hypothetical exposures using Staphylococcus aureus and coagulase negative staphylococci (CNS), differences in identification of antimicrobial resistance (AMR) based upon choice of method, and environmental and demographic factors driving Porcine Reproductive and Respiratory Syndrome virus (PPRSv) including the quantification of its spatial variation across the United States of America (U.S.A.). Maintenance of freedom from Bovine Herpes Virus type 1 (BoHV1) circulation (which causes IBR) in Dutch cattle, in the face of cattle imports, was investigated using a stochastic simulation model by Santman-Berends et al. The model predicted basic risk and evaluated the efficacy of risk mitigating scenarios which included testing prior to import, import restrictions and vaccination. The model suggested that IBR infected animals are regularly imported, with an estimate of 571 herds affected upon import, mostly due to latent infections. It also suggested that acutely infected imported animals would mostly impact veal herds. The scenarios most successful in reducing import risk included allowing importation only from countries with a certain disease status, or vaccinating calves combined with testing older cattle; the latter being most feasible for stakeholders. Importation risk seemed most reduced by combining testing and vaccination strategies. BVD, a major production disease of cattle, can be vertically transmitted. Transient postnatal infections lead to immunologically protected cattle. However, during a pregnancy window, in utero embryo infection can occur leading to persistently infected (PI) calves; a major risk for BVD spread, but also an efficient target for control. Strategies to identify PI animals for removal include tissue tag testing and serological screening. Since 2013, all Irish new born calves are mandatorily tissue tag tested for BVD, reducing PI incidence substantially. Recently, stakeholders including farmers have been interested, due to potential cost savings, in using an indirect testing strategy. Thulke et al. helped to inform this debate. They quantified the expected strategic, budgetary and implementation benefits of strategy change by reviewing national eradication programme data and strategy performance predictions from an expert system model. They identified some drawbacks to changing strategy including a loss of epidemiological information to allow real-time monitoring of eradication progress, and reduced effectiveness in terms of time to eradication because PI removal would not be enforced, and some positive costs savings for 28% of herds. However, these were negligible in half of the cases. Haine et al. also explored the impact of imperfect testing regimes, in relation to udder health in a simulated hypothetical cohort study and scenarios describing S. aureus and CNS. They evaluated the relative impact of selection and misclassification biases resulting from incident intramammary infection (IMI) misclassification on measures of (IMI) disease frequency (incidence) and of association with hypothetical exposures (odds ratio; OR), estimated using Markov Chain Monte Carlo simulations. For the S. aureus scenario, a pathogen with a low incidence, biases were small for disease incidence. In contrast, diagnostic errors led to important selection and misclassification biases for CNS, which have a high incidence. The OR for association with exposure also showed little bias for S. aureus, compared to large misclassification bias for CNS, which showed little improvement when varying sampling strategies to improve test sensitivity or specificity, or using a two out of three interpretation for IMI definition. The authors concluded that increasing sampling or testing can prevent bias in some situations but efforts can be spared in others. When designing longitudinal studies, evaluating potential biases and best sampling strategy is as critical as the choice of diagnostic test. AMR increasingly threatens global public health, with unquantified bidirectional transmission in humans, animals and the environment. Appropriate measurement of resistance is needed to quantify rates of transmission and assess the costs and benefits of reduced antimicrobial usage in livestock. In their study, Humphry and others explored differences in the identification of ampicillin and nalidixic acid resistance in cattle or sheep faeces, arising from choice of measurement, including screening samples by “streaking” direct culture on to treated plates, and determining minimum inhibitory concentration (MIC) using published thresholds and individual isolates. Direct culture resulted in more than double the number

Association of clinical signs after acute Schmallenberg virus infection with milk production and fertility in Swiss dairy cows

Since its first occurrence in August 2011 in Germany and the Netherlands, the Schmallenberg virus (SBV) spread rapidly across Europe, where it caused production losses and abortions in ruminants as well as congenital malformations in the offspring of affected animals. Several studies have investigated the impact of SBV on fertility and production parameters in dairy cows at herd level. However, the impact of clinical disease at the animal level remained undetermined. This study aimed at estimating the impact of clinical disease during and after an infection with SBV on production and fertility parameters in individual Swiss dairy cows. Sixty-seven case and twenty-four control herds were selected according to whether cows had been showing clinical signs indicative of SBV during the epidemic from July to December 2012 in Switzerland. Of these 91 farms, production and fertility data from 388 cows with clinical signs from case herds were collected over a time period of four years, and compared to data from 932 cows without clinical signs originating from case or control herds. Milk yield, somatic cell count, number of inseminations and non-return at day 56 were analysed by means of hierarchical multivariable regression analysis. A significant drop in milk yield was observed in all groups during the SBV epidemic compared to the time before the infection, which amounted to 1.9kg per test day for clinical animals, 1.1kg for non-clinical animals from case herds and 0.6kg for non-clinical animals from control herds. A prolonged effect on milk yield was observed in clinical cows for about one year, suggesting that animals with clinical disease might not return to their previous milk production level in the current lactation after an acute infection with SBV. Clinical animals showed a significantly higher somatic cell count during the epidemic compared to the time before the infection. The number of inseminations per cow and production cycle was higher for clinical animals during the epidemic compared to the time periods before and after, but not significantly higher than for non-clinical animals from case and control herds. No difference regarding non-return at day 56 was found. Although the overall impact of the SBV epidemic in Switzerland was limited, the consequences could be substantial in farms with a high prevalence of clinical disease.

SVEPM 2015—Controlling disease across species using emerging techniques in epidemiology and economics applied to animal health, Society of Veterinary Epidemiology and Preventive Medicine conference Ghent, Belgium 25–27 March 2015

At the 2015 Annual Meeting of the Society for Veterinary Epiemiology and Preventive Medicine (SVEPM) in Ghent, Belgium, everal studies were presented which applied new and mixed ethodologies in the search for explanations and solutions to preent disease in animals and humans. Among the studies presented, he eight published in this special edition of Preventive Veterinary edicine demonstrate both the high quality science presented at his conference and, as pointed out by one of the keynote speakers, hat preventive veterinary medicine is an important contributor to ustainable animal production today. The papers focus on a wide spectrum of topics and approaches, ncluding both qualitative and quantitative methods investigatng opinions and drivers for proactive animal health planning in heep, a participatory method for surveillance evaluation, sample ize considerations for livestock movement network data, spaiotemporal analyses combined with cost-benefit considerations f a tick-borne disease, economic impact of subclinical disease in attle, state-of-the-art epidemiological analyses of antimicrobial esistance trends in multiple species and analysis of register data n dog diseases. In the first paper, Bellet et al. used qualitative interviews with 2 veterinarians in central, south-west and the north of England nd Wales to understand veterinarians’ opinions on preventative dvice and drivers for current services to sheep farmers. This was ollowed up by quantitative analysis of answers from 147 veterinarans who responded to a postal questionnaire of belief statements. hree main factors were identified: motivation for proactiveness, erceived capability to offer preventative services and perceived pportunity to deliver these services. These factors were associted with the proportion of time spent in an advisory role with heep clients. Such insight into the nature and drivers of veterinarans’ behaviour and beliefs can help in designing efficient strategies imed at promoting proactive health services offered by veterinarans on sheep farms. Calba et al. illustrated how qualitative research methods can e used to improve surveillance systems. They used eight individal semi-structured interviews and three focus groups of sixteen ssential stakeholders, conducted using participatory approaches, o evaluate two attributes of surveillance for African swine fever on