Simulation modelling as a tool for evaluating surveillance programmes for detection of the Asian honeybee mite (Varroa destructor) in the South Island of New Zealand

AIM: To use a simulation model of the spread of the Asian honeybee mite (Varroa destructor) amongst apiaries, to evaluate a series of detection surveillance programmes for the South Island of New Zealand.

METHODS: Five potential incursion sites into the South Island were selected. A stochastic spatial simulation model, Varroa_sim, was adapted to simulate spread of the mite from these sites as a series of silent-phase propagating epidemics. The study population comprised all apiaries in the South Island registered in the Ministry of Agriculture and Forestry's (MAF's) apiary database in 2003. Six different surveillance programmes were simulated to try and detect the mite. Three of these were the actual multi-stage sampling plans conducted during the autumn (March–May) of 2001, 2002 and 2003, and the other three involved simple random sampling with sampling fractions equivalent to the actual numbers of apiaries tested in each of those years. The relative performances of the different surveillance plans were evaluated in terms of their ability to detect the mite early before it had spread too far and whilst there might still be a chance of eradication.

RESULTS: There were 13,798 registered apiaries in the South Island with valid map coordinates in the apiary database at the time of the study. The model generated 50 epidemics against which the various surveillance programmes were evaluated. The actual surveillance programmes conducted during the autumn of 2001 and 2002 generally performed fairly well in detecting the mite. The programme conducted in autumn 2003 detected the mite reasonably well in high-risk areas, but was very poor in low-risk areas. The simple random sampling strategies performed surprisingly well, and their relative rankings were proportional to the sampling fractions employed.

CONCLUSIONS: This study showed the value in using a spatial simulation model to generate plausible silent-phase epidemics, against which detection surveillance programmes could be evaluated, in ways that would otherwise not be possible.     

Spatial epidemiology of the Asian honey bee mite (Varroa destructor) in the North Island of New Zealand

We describe the spatial epidemiology of Varroa destructor infestation among honey bee apiaries in the greater Auckland area of the North Island of New Zealand. The study population was comprised of 641 apiaries located within the boundaries of the study area on 11 April 2000. Cases were those members of the study population declared Varroa-infested on the basis of testing conducted between April and June 2000. The odds of Varroa was highest in apiaries in the area surrounding transport and storage facilities in the vicinity of Auckland International Airport. A mixed-effects geostatistical model, accounting for spatial extra-binomial variation in Varroa prevalence, showed a 17% reduction in the odds of an apiary being Varroa infested for each kilometre increase in the squared distance from the likely site of incursion (95% Bayesian credible interval 7–28%). The pattern of spatially autocorrelated risk that remained after controlling for the effect of distance from the likely incursion site identified areas thought to be ‘secondary’ foci of Varroa infestation initiated by beekeeper-assisted movement of infested bees. Targeted investigations within these identified areas indicated that the maximum rate of local spread of Varroa was in the order of 12 km/year (interquartile range 10–15 km/year).     

Spatial epidemiology of the Asian honey bee mite (Varroa destructor) in the North Island of New Zealand

We describe the spatial epidemiology of Varroa destructor infestation among honey bee apiaries in the greater Auckland area of the North Island of New Zealand. The study population was comprised of 641 apiaries located within the boundaries of the study area on 11 April 2000. Cases were those members of the study population declared Varroa-infested on the basis of testing conducted between April and June 2000. The odds of Varroa was highest in apiaries in the area surrounding transport and storage facilities in the vicinity of Auckland International Airport. A mixed-effects geostatistical model, accounting for spatial extra-binomial variation in Varroa prevalence, showed a 17% reduction in the odds of an apiary being Varroa infested for each kilometre increase in the squared distance from the likely site of incursion (95% Bayesian credible interval 7–28%). The pattern of spatially autocorrelated risk that remained after controlling for the effect of distance from the likely incursion site identified areas thought to be ‘secondary’ foci of Varroa infestation initiated by beekeeper-assisted movement of infested bees. Targeted investigations within these identified areas indicated that the maximum rate of local spread of Varroa was in the order of 12 km/year (interquartile range 10–15 km/year).     

Efficacy of repeated trickle applications of oxalic acid in syrup for varroosis control in Apis mellifera: influence of meteorological conditions and presence of brood

Oxalic acid field trails for the control of varroosis (Varroa destructor) were carried out in an apiary located on the Mt. Imittos (Attica, Greece). The colonies received four successive applications (approximately one every 16 days) with 4.2% oxalic acid (OA) and 60% sugar solution by trickling method with two alternative types of syringes (an automatic self-filling dosing and a single-use) from the broodright to broodless period. The results indicate that the first three applications (from 6th October to 25th November-broodright period) resulted in 65.3% cumulative mite mortality, while only the last application (after the 26th November-broodless period) resulted in 77.3% mite mortality. Very low outern temperatures reduce to the minimum the bee movability, which may result into a slower development of the OA efficacy. No poor colony growth or queen loss were observed even if the bee colonies were received the four successive OA applications with the last one taken place at a very low outern temperature (6.2 degrees C). The trickling method using an automatic-filling syringe seems to be a very quick way for applying oxalic acid in large apiaries (approximately 150hives/h).     

2009--2010年转地蜂场组织结构与人文素质分析——基于浙江省缙云县80家蜂场的调研

对浙江省缙云县2009～2010年80家转地蜂场的组织结构与人文素质进行了调查分析,结果表明：80家转地蜂场全部是一户一家的家庭结构专业化养蜂场。蜂场以2～4人为主,人均养蜂数量为50群,蜂场规模与往年相比有所扩大;蜂农平均年龄为36～37岁,50岁以下分别占93．69％和89．79％;蜂农养蜂工龄平均为12年,与往年基本类似;蜂农文化程度：小学分别占13．06％和9．79％;初中分别占76．58％和81．28％;高中分别占10．36％和8．51％;蜂场订阅蜂业科技刊物分别占82．50％和78．75％;蜂场组织化程度分别为82．50％和78．75％,比往年有所提高。但是,蜂农的小农经济意识根深蒂固,亟待解决。     

2011年转地蜂场生产蜂花粉经济效益调查

调查了浙江省缙云县80家转地蜂场2011年生产蜂花粉的经济效益,结果显示:2011年蜂花粉平均产量3.49 kg/群,同比增长175.79%,平均产值87.70元/群,同比增长160.86%,占群总产值的7.85%,为8年来最高。其中,蜂花粉收入前10位蜂场的蜂群饲养量平均168群/家,蜂花粉收入35 007元/家(207.88元/群),占蜂场年总收入的16.48%,表明蜂花粉生产在提高蜂农经济效益中大有可为。在与历年数据综合比较分析的基础上,探讨了蜂花粉生产的经济效益以及存在的问题,并提出了一些合理化建议。     

Salmonella Brandenburg - emergence of a new strain affecting stock and humans in the South Island of New Zealand

AIMS: To report information on the spread of a new strain of Salmonella Brandenburg, which affected livestock and humans in the South Island of New Zealand, and a series of small case studies designed to investigate potential transmission of infection. METHODS: Information on the occurrence and spread of S. Brandenburg in livestock was gathered from laboratory diagnostic submissions, from case studies on the faecal excretion rate in ewes, carrier status of black-backed gulls (Larus dominicanus), spread of S. Brandenburg organisms in sheep yards, infection in lambs going to meat plants, and from post-abortion pathological changes in the reproductive tract of ewes. RESULTS: A newly recognised strain of S. Brandenburg was first diagnosed in aborting sheep from a flock in mid Canterbury in the South Island in 1996. Subsequently, the disease spread to other farms in mid and south Canterbury in 1997 and to Southland and Otago in the lower half of the South Island in 1998-2003. In 1999, the same strain was responsible for abortions in cattle and gastroenteritis in calves and adult cattle. The same strain of bacterium also caused disease in horses, goats, deer, pigs and humans. Spread of the disease on farms was strongly associated with aborting ewes, which resulted in considerable environmental contamination. During the abortion season, black-backed gulls appeared to spread the disease to other farms. Other potential sources of infection were carrier sheep, contaminated water sources and contaminated sheepyard dust. Damage to the reproductive tract may affect the ability of surviving ewes to conceive. CONCLUSION: Important features of this disease are its high morbidity and mortality within a flock or herd, rapid local spread and its role as an occupational, health and safety risk to farm workers and their families.     

2007-2010年转地蜂场养蜂规模经济效益分析——基于浙江省缙云县80家蜂场的调研

养蜂规模是影响蜂场经济效益的主要因素之一,转地蜂场何等养蜂规模经济效益最好,是业内人士关注的热点之一。2007-2010年,我们对浙江省缙云县80家以生产蜂蜜为主、生产蜂王浆、蜂花粉为辅的转地蜂场养蜂规模经济效益进行了跟踪调查。结果表明,在目前的转地养蜂生产方式和生产力水平下,蜂场规模以2-4人为主,其中,4人规模的家庭蜂场饲养185-195群西方蜜蜂,为最佳的适度规模;5人蜂场的经济效益最佳,但发展缓慢,值得关注与期待。     

Ovine Johne's disease in Australia--the first 20 years

OBJECTIVE: To review the history of ovine Johne's disease in Australia. PROCEDURE: Relevant publications and reports were identified and reviewed to document the spread of ovine Johne's disease (OJD) from 1980 until the end of 2000, as well as the response of industry and government to the spread of this disease. RESULTS: OJD was first diagnosed in the central tablelands region of New South Wales in 1980. Since then it has spread, either from the initial focus or through separate introductions so that by December 2000 a total of 823 infected flocks had been identified. Cases have been confirmed in New South Wales, Victoria, the Australian Capital Territory, on Flinders Island in Tasmania, on Kangaroo Island in South Australia and in Western Australia. In early 1999, agreement was reached to fund and implement a 6-year, $40 million National OJD Control and Evaluation Program (NOJDP). This program is jointly funded by the sheep industries (national and state), and Commonwealth and State governments, and is managed by Animal Health Australia. CONCLUSION: A national program is now in place to support the control of OJD and research to determine the feasibility and cost-effectiveness of eradication. The development of new diagnostic techniques, such as abattoir surveillance and pooled faecal culture, provide opportunities to refine surveillance strategies and to define better the distribution and prevalence of this disease, as required by the national program. Effective control measures, combined with quality surveillance data, will enable informed decision making for the future national management of OJD.     

Risk based surveillance for early detection of low pathogenic avian influenza outbreaks in layer chickens

Current knowledge does not allow the prediction of when low pathogenic avian influenza virus (LPAIV) of the H5 and H7 subtypes infecting poultry will mutate to their highly pathogenic phenotype (HPAIV). This mutation may already take place in the first infected flock; hence early detection of LPAIV outbreaks will reduce the likelihood of pathogenicity mutations and large epidemics. The objective of this study was the development of a model for the design and evaluation of serological-surveillance programmes, with a particular focus on early detection of LPAIV infections in layer chicken flocks. Early detection is defined as the detection of an infected flock before it infects on average more than one other flock (between-flock reproduction ratio R_f < 1), hence a LPAI introduction will be detected when only one or a few other flocks are infected. We used a mathematical model that investigates the required sample size and sampling frequency for early detection by taking into account the LPAIV within- and between-flock infection dynamics as well as the diagnostic performance of the serological test used. Since layer flocks are the target of the surveillance, we also explored whether the use of eggs, is a good alternative to sera, as sample commodity. The model was used to refine the current Dutch serological-surveillance programme. LPAIV transmission-risk maps were constructed and used to target a risk-based surveillance strategy. In conclusion, we present a model that can be used to explore different sampling strategies, which combined with a cost-benefit analysis would enhance surveillance programmes for low pathogenic avian influenza.     

Disease properties, geography, and mitigation strategies in a simulation spread of rinderpest across the United States

ABSTRACT: For the past decade, the Food and Agriculture Organization of the United Nations has been working toward eradicating rinderpest through vaccination and intense surveillance by 2012. Because of the potential severity of a rinderpest epidemic, it is prudent to prepare for an unexpected outbreak in animal populations. There is no immunity to the disease among the livestock or wildlife in the United States (US). If rinderpest were to emerge in the US, the loss in livestock could be devastating. We predict the potential spread of rinderpest using a two-stage model for the spread of a multi-host infectious disease among agricultural animals in the US. The model incorporates large-scale interactions among US counties and the small-scale dynamics of disease spread within a county. The model epidemic was seeded in 16 locations and there was a strong dependence of the overall epidemic size on the starting location. The epidemics were classified according to overall size into small epidemics of 100 to 300 animals (failed epidemics), epidemics infecting 3 000 to 30 000 animals (medium epidemics), and the large epidemics infecting around one million beef cattle. The size of the rinderpest epidemics were directly related to the origin of the disease and whether or not the disease moved into certain key counties in high-livestock-density areas of the US. The epidemic size also depended upon response time and effectiveness of movement controls.     

2011-2012年转地蜂场养蜂规模经济效益调查

养蜂规模是影响蜂场经济效益的主要因素之一,尤其是在转地蜂场生产成本高、风险系数大等条件下.怎样的养蜂规模能取得最佳经济效益（适度养蜂规模）是业内普遍关注的热点.2011-2012年,跟踪调查了浙江省缙云县80家转地蜂场养蜂规模经济效益,结果发现,2011年的适度养蜂规模为4人蜂场平均饲养186群西方蜜蜂;2012年的适度养蜂规模为3人蜂场平均饲养158群西方蜜蜂.这表明转地蜂场适度养蜂经营规模处于动态变化中.调查结果对指导转地蜂场调整适度养蜂规模,增加经济效益具有现实意义.     

Modelling the effect of surveillance programmes on spread of bovine herpesvirus 1 between certified cattle herds

For the eradication of an infectious agent, like bovine herpesvirus 1 (BHV-1), surveillance and certification can be used to reduce the transmission between herds. The goal of surveillance is that a certified herd that becomes infected is detected timely so that infection of several other certified herds is prevented. What counts is whether the reproduction ratio R, i.e. the average number of certified herds infected by one infected certified herd can be kept below 1. To support policy makers in making decisions about the minimal demands for a surveillance programme in an eradication campaign of BHV-1 in cattle, two mathematical models were investigated. With these models, the basic reproduction ratio between herds was calculated. The surveillance programmes were characterised with sample size, sampling frequency, test sensitivity, herd size, vaccination status, and contacts between herds. When R between herds is below 1, then the surveillance programme is sufficiently good to prevent spread of infection, provided that R is estimated well. In the model based on bulk milk testing sample size was replaced by a threshold at which bulk milk can be found positive. The R between herds was mainly influenced by the vaccination status, sampling frequency, and contacts between herds. Herd size moderately affected the outcome. Test sensitivity and sample size, however, were of minor importance. If herds of 50 cows became free of BHV-1 without vaccination, then spread of infection between herds might be prevented when animals within herds are sampled once a year (milk or blood samples). This frequency needs to be intensified, being twice a year, for larger herds and/or herds with extensive contacts with other herds. When bulk milk is sampled instead, sampling should be done at least every 5 months and more intensively, being each month, with larger herd sizes and more contacts between herds.     

Design and Results of an Intensive Monitoring Programme for Avian Influenza in Meat‐Type Turkey Flocks During Four Epidemics in Northern Italy

Surveillance programmes for low pathogenicity (LPAI) and high pathogenicity avian influenza (HPAI) infections in poultry are compulsory for EU Member States; yet, these programmes have rarely been evaluated. In Italy, following a 1999 HPAI epidemic, control measures, including vaccination and monitoring, were implemented in the densely populated poultry area (DPPA) where all epidemics in Italy have been concentrated. We evaluated the monitoring system for its capacity to detect outbreaks rapidly in meat‐type turkey flocks. The evaluation was performed in vaccination areas and high‐risk areas in the DPPA, in 2000–2005, during which four epidemics occurred. Serum samples and cloacal swabs were taken from vaccinated birds and unvaccinated (sentinel) birds. We compared the detection rate of active, passive and targeted surveillance, by vaccination status, using multinomial logistic regression. A total of 13 275 samplings for serological testing and 4889 samplings for virological testing were performed; 6315 production cycles of different bird species were tested. The outbreaks detection rate in meat‐type turkeys was 61% for active surveillance (n = 222/363 outbreaks), 32% for passive surveillance and 7% for targeted surveillance. The maximum likelihood predicted values for the detection rates differed by vaccination status: in unvaccinated flocks, it was 50% for active surveillance, 40% for passive surveillance and 10% for targeted surveillance, compared to respectively 79%, 17% and 4% for vaccinated flocks. Active surveillance seems to be most effective in detecting infection, especially when a vaccination programme is in place. This is the first evaluation of the effectiveness of different types of surveillance in monitoring LPAI infections in vaccinated poultry using field data.     

The effectiveness of classical swine fever surveillance programmes in The Netherlands

Consequences of classical swine fever (CSF) epidemics depend on the control measures, but also on the number of infected herds at the end of the high-risk period (HRP). Surveillance programmes aim to keep this number as low as possible, so the effectiveness of surveillance programmes can be measured by the number of infected herds at the end of the HRP. In this paper, an evaluation of the effectiveness of the following five Dutch CSF surveillance programmes is presented: (1) routine gross pathology of severely diseased pigs; (2) routine virological tests of tonsils of all pigs, submitted under 1; (3) daily clinical observation by the farmer; (4) periodic clinical inspection by a veterinarian; (5) leucocyte counts in blood samples from diseased animals on a herd where antimicrobial 'group therapy' is started. The evaluation was done by a modelling study, in which virus transmission, disease development, and actions and diagnostic tests in surveillance programmes were simulated. Also, the yearly costs of the programmes were calculated, and direct costs of CSF epidemics were related to the number of infected herds at the end of the HRP. It appeared that the current Dutch surveillance programmes, without the leucocyte counts, keep the number of infected herds at the end of the HRP below 20 with 95% probability. Leaving out the most-expensive programme of periodic inspection (12.5M per year) does not change this result - indicating that (for CSF surveillance) the programme could well be stopped. If the leucocyte programme, which is currently not effective due to the low sample submission rate, optimally were applied, the 95th percentile could be reduced to 10 infected herds. However, whether application is beneficial is unclear, because of uncertainty of the economic benefits due to the many expected false-positive herds each year.     

蜂蟹螨(Varroa destructor)对福化利抗药性及其防治的研究

建立培养皿药膜法进行蜂蟹螨福化利(Fluvalinate)抗药浓度检测方法。分别以福化利浓度为0、12.5、25、50、100mg/L进行台湾5处蜂场蜂蟹螨抗福化利剂量调查,经回归分析,计算LC50之浓度介于23.75～79.25mg/L之间,比意大利抗性螨385～857mg/L仍低很多,显示抗药性尚未大幅增加。以隔落螨法防治蜂蟹螨平均每日可捕捉44.7～49.1只。比较隔落螨法、割雄蜂蛹加隔落螨法、蚁酸加隔落螨法、福化利防治法的效果,当蜂蟹螨密度不高时,可采用隔落螨法或加割雄蜂蛹方式进行防治,蜂蟹螨密度高时,可先以福化利、蚁酸进行1～2次防治,再配合隔落螨法,将可达到长期防治效果。     

Statistical evaluation of classical swine fever surveillance plans in Italy (1995-2003)

Summary Surveillance plans were carried out in Italy from 1995 to 2003, with the main aim of controlling the possible circulation of low-virulence classical swine fever viral strains. The repetition of a serological monitoring programme over several years, with constantly negative results, can prove the absence of the infection while increasing the degree of confidence. In our case, in 2003, after eight repetitions of the surveillance plan, the probability that there was at least one infected farm reached 0.006%. Therefore, on the basis of the results of the sampling carried out from 1995 to 2003, we may state that there is no endemic infection, even because of a low virulence virus, in continental Italy.     

Statistical Evaluation of Classical Swine Fever Surveillance Plans in Italy (1995–2003)

Surveillance plans were carried out in Italy from 1995 to 2003, with the main aim of controlling the possible circulation of low‐virulence classical swine fever viral strains. The repetition of a serological monitoring programme over several years, with constantly negative results, can prove the absence of the infection while increasing the degree of confidence. In our case, in 2003, after eight repetitions of the surveillance plan, the probability that there was at least one infected farm reached 0.006%. Therefore, on the basis of the results of the sampling carried out from 1995 to 2003, we may state that there is no endemic infection, even because of a low virulence virus, in continental Italy.     

Detection and surveillance for animal trichinellosis in GB

The zoonotic disease trichinellosis is considered one of the re-emerging diseases with surveillance and control methods constantly gaining more importance worldwide. Recent change in European Union (EU) legislation introduces Trichinella-free production, and the possibility of risk-based monitoring for Trichinella in pigs. This has increased the role of wildlife surveillance programmes and their impact on protecting human health as well as highlighted the need for harmonised surveillance protocols and test methods for these infections. A modified digest method, based on the EU reference method for Trichinella testing of pig meat, was used to screen foxes present in Great Britain (England, Scotland and Wales) for trichinellosis. The method was validated using batched pools of 10 g foreleg muscle from up to 20 foxes (maximum amount 200 g). The method gave an average trichinae recovery rate of 71% for spiked samples. Assuming this recovery rate applies to all contaminated samples, then the test sensitivity would be 70% for all tissue samples with 0.1 trichinae per 10 g of foreleg muscle, 99.9% for samples with 1 trichinae per 10 g, and 100% for samples with 2 or more trichinae per 10 g. In two separate studies, conducted between 1999 to 2001 (Smith et al., 2003) and 2003 to 2007, over 3500 wild foxes have been screened for Trichinella with negative results. In the second study reported here, foxes were collected from locations throughout Great Britain using a stratified sampling method based on fox population densities. All work was conducted in compliance with appropriate quality assurance systems, latterly under ISO 9001. Results to date indicate the national prevalence of trichinellosis in foxes is <0.001 based on a 10 g individual sample size, an infection level of 1 larva per gram (l pg) and 95% confidence interval. This, together with no reports of trichinellosis in domesticated pigs, suggests that Britain can be considered a region of negligible risk of trichinellosis.     

Occurrence of acute paralysis virus of the honey bee (Apis mellifera) in a Hungarian apiary infested with the parasitic mite Varroa jacobsoni.

Viruses of the honey bee have been known for a long time; however, recently the attention of scientists and apiculturalists has turned towards the relationship between these viruses and the parasitic mite Varroa jacobsoni. Although clinical symptoms indicated the presence of some of the viruses of bees in Hungary, none have previously been isolated or identified. During July unusual adult bee and brood mortality was observed in some colonies of an apiary in Budapest known to be infested with Varroa jacobsoni. Large amounts of acute paralysis virus (APV) were detected serologically in healthy honey bee pupae killed by the injection of a bacteria-free extract of diseased adult bees. Crystalline arrays of 30 nm particles were seen in ultrathin sections of the tissues of injected pupae and naturally infected adult bees. In spite of the application of acaricide treatments the bee population in several colonies had collapsed by the end of summer and the apiary suffered severe wintering losses.