Evaluation of effectiveness and efficiency of wild bird surveillance for avian influenza

This study aimed to assess which method of wild waterbird surveillance had the greatest probability of detecting highly pathogenic avian influenza (HPAI) H5N1 during a period of surveillance activity, the cost of each method was also considered. Lake Constance is a major wintering centre for migratory waterbirds and in 2006 it was the site of an HPAI H5N1 epidemic in wild birds. Avian influenza surveillance was conducted using harmonised approaches in the three countries around the lake, Austria, Germany and Switzerland, from 2006–2009. The surveillance consisted of testing birds sampled by the following methods: live birds caught in traps, birds killed by hunters, birds caught in fishing nets, dead birds found by the public and catching live Mute Swans (Cygnus olor); sentinel flocks of Mallards (Anas platyrhynchos) were also used. Scenario tree analysis was performed including sensitivity analysis, followed by assessment of cost-effectiveness. Results indicated that if HPAI H5N1 was present at 1% prevalence and assuming HPAI resulted in bird mortality, sampling dead birds found by the public and sentinel surveillance were the most sensitive approaches despite residual uncertainty over some parameters. The uncertainty over the mortality of infected birds was an influential factor. Sampling birds found dead was most cost-effective, but strongly dependent on mortality and awareness of the public. Trapping live birds was least cost-effective. Based on our results, we recommend that future HPAI H5N1 surveillance around Lake Constance should prioritise sentinel surveillance and, if high mortality is expected, the testing of birds found dead.     

Adapting a scenario tree model for freedom from disease as surveillance progresses: The Canadian notifiable avian influenza model

Scenario tree models with temporal discounting have been applied in four continents to support claims of freedom from animal disease. Recently, a second (new) model was developed for the same population and disease. This is a natural development because surveillance is a dynamic process that needs to adapt to changing circumstances – the difficulty is the justification for, documentation of, presentation of and the acceptance of the changes.     

基于最大熵模型对蓝舌病病毒传播媒介库蠓在中国分布特征的研究

蓝舌病是由蓝舌病毒(BTV)引起的一种非接触性传染病,主要侵害反刍动物,库蠓是蓝舌病毒传播最重要的媒介生物。本研究基于尖喙库蠓地理分布数据及环境数据,利用最大熵生态位模型(MaxEnt)对尖喙库蠓在中国大陆的分布情况进行了预测,并评估了环境变量对尖喙库蠓分布的影响。结果显示,最适合尖喙库蠓生存的地区主要分布在中国的西北和东北部分地区,以及南方的大部分地区;Jackknife分析结果显示,土壤有效水含量(25%)、最冷月最低温(18.1%)、最干月降雨量(18%)、平均最大风速(13.2%)是影响尖喙库蠓分布最主要的4个环境因子,其中最干月降雨量是模型中影响尖喙库蠓分布的最重要环境变量。本研究首次将这种生态位模型用于预测中国库蠓的分布,为蓝舌病的预防控制工作提供参考依据,同时也为库蠓监测管理提供信息。     

Demonstrating freedom from disease using multiple complex data sources 1: a new methodology based on scenario trees

Current methods to demonstrate zone or country freedom from disease are based on either quantitative analysis of the results of structured representative surveys, or qualitative assessments of multiple sources of evidence (including complex non-representative sources). This paper presents a methodology for objective quantitative analysis of multiple complex data sources to support claims of freedom from disease. Stochastic scenario tree models are used to describe each component of a surveillance system (SSC), and used to estimate the sensitivity of each SSC. The process of building and analysing the models is described, as well as techniques to take into account any lack of independence between units at different levels within a SSC. The combination of sensitivity estimates from multiple SSCs into a single estimate for the entire surveillance system is also considered, again taking into account lack of independence between components. A sensitivity ratio is used to compare different components of a surveillance system. Finally, calculation of the probability of country freedom from the estimated sensitivity of the surveillance system is illustrated, incorporating the use and valuation of historical surveillance evidence.     

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.     

Animal-based national surveillance for zoonotic disease: quality, limitations, and implications of a model system for monitoring rabies

Surveillance for zoonotic diseases among wildlife is a research and public health challenge. The inherent limitations posed by the requisite human–animal interactions are often undefined and underappreciated. The national surveillance system for animal rabies in the United States was examined as a model system; reporting of animal rabies is legally mandated, each case of rabies is laboratory confirmed, and data have been consistently collected for more than 50 years. Factors influencing the monthly counts of animal rabies tests reported during 1992–2001 were assessed by univariate and multivariable regression methods. The suitability of passively collected surveillance data for determining the presence or absence of the raccoon-associated variant of rabies within states and within individual counties was assessed by determining critical threshold values from the regression analyses. The size of the human population and total expenditures within a county accounted for 72% and 67%, respectively, of the variance in testing. The annual median number of rabies tests performed was seven for counties without rabies, 22 for counties with non-raccoon rabies, and 34 for counties with raccoon rabies. Active surveillance may be required in locales with sparse human populations when a high degree of confidence in the status of rabies is required.     

Evaluation of cervical radiographs in Dutch Warmblood horses,using a novel radiographic grading system for the cervical articular process joints

Clinical and radiographic examination of the cervical spine has been of increasing interest in the prepurchase examination and clinical work-up conducted for horses. The objective of this study was to describe a grading system useful for evaluating all the cervical articular process joints (cAPJs). Additionally, the findings of the cervical radiographs (occiput, cAPJ and intercentral joint space grading, intra- and intervertebral sagittal ratios, and intervertebral disc width measurements) were reported, and their association with clinical complaints in a large group of Dutch Warmblood horses (n = 598) were investigated. Significant associations were found between cAPJ radiographic grades and clinical complaints using the chi-squared test (C2-3 [P = 0.01], C5-6 [P = 0.006], C6-7 [P < 0.001], and C7-T1 [P = 0.02]). Higher occiput grades were significantly associated with clinical complaints (chi-squared test, P = 0.005). A large variability was found for intra- and intervertebral ratios and minimum intercentral joint space in the control group, but no significant association between intercentral joint space and clinical complaints was observed using the Kruskal–Wallis test followed by post hoc testing with the Wilcoxon rank sum test with a Bonferroni correction. The main limitations of this study were that only information regarding localisation was used for the statistical analyses, without any other details of the clinical complaints. Furthermore, clinical records were retrospectively reviewed, and a bias towards cervical findings in the clinical data recordings should be considered. It was concluded that knowledge of the distribution of the radiographic findings evaluated in this study and their associated clinical relevance can be useful in reaching a science-based diagnosis in daily practice.