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Surveillance approaches for wildlife diseases often are based on strategies devised for livestock diseases. Following standard protocols, surveillance sometimes continues after apparent disease elimination. However, in the case of recurrent wildlife diseases that cause decisive morbidity and mortality, efficient and effective surveillance strategies might need to be more dynamic and adaptable to the actual epidemic situation. Here, we evaluated existing surveillance schemes by reanalyzing historic data on three wildlife diseases in Europe: rabies, classical swine fever, and avian influenza. We analyzed the aims of different surveillance activities and the way in which they were performed. Our analyses revealed that static, nonadaptive surveillance was a suboptimal approach. Consequently, we propose and discuss a more adaptive alternative scheme of situation-based surveillance for recurrent wildlife diseases that cause readily recognizable morbidity and mortality.

Over the last fifteen years or so, classical rabies in terrestrial wildlife has been eliminated from large areas of Western Europe. Over the next few years, terrestrial rabies is likely to occur only east of a line from the Baltic Sea to the Black Sea; the overall aim is to eliminate terrestrial rabies from the whole European Union. Elimination of rabies from the less rich countries of Eastern Europe, and the protection of Europe against a resurgence of rabies in the longer term requires modifications to existing OIE and WHO strategies. Here we discuss the options available to eliminate rabies in wildlife while taking account of financial cost, and how to maintain a 'cordon sanitaire' along the eastern boundary of the EU in order to protect the rabies-free areas from rabies incursion. Minimising financial costs at the national level is obviously essential, considering the competing priorities for development and health. This could be achieved either by increasing external funding (for example by the EU) and/or by changing the currently agreed vaccination strategy to reduce costs; any such change must not substantially reduce the chances of rabies elimination. A cordon sanitaire might be placed outside the economic area of the EU, to protect the whole of the EU, or it might be placed within the easternmost countries to ensure logistical consistency of vaccination. Policy must also anticipate an emergency due to rabies breaking out in a previously freed region. Strategic planning may be complicated by the increasing range and abundance of the raccoon dog, an introduced species that is increasingly important as a host for fox rabies. It is argued here that models help to evaluate altemative strategies, exploring options for optimising costs by minimising bait density and frequency or by reducing the vaccination area.

Spatio-temporal survey data often form the main decision support in disease management. Consequently, disease managers rely on adequate description of the data supplied from epidemiological analysis. Practically speaking, such a description comprises of a visualisation, a deduced hypothesis and a statistical evaluation of the hypothesis. Prior to the application of traditional methods of data visualisation and hence data description, an aggregation of the data is required. This paper illustrates the resulting uncertainty in hypotheses that can be generated by traditional analytical techniques. Additionally, a method of avoiding this typical drawback in traditional data exploration is demonstrated: This is the use of data movies. Data from a 10-year study on the spread of pseudorabies virus (PrV) infections in wild boar populations were revisited. The visualisation of the data using a data movie instead of using traditional approaches for the first time enabled immediate observation of spreading infection in time and space. This dynamic perception of the spread drastically changes the understanding of the epidemiology of the virus. The paper demonstrates how data movies can account for the complete information contained within the data set. It is concluded that data movies can provide a more appropriate starting point. We recommend the data movie approach as an important addition in the epidemiological toolbox, because data movies can easily be integrated into the usual demonstration and publication process.

BackgroundRabies is the most important viral zoonosis from a global perspective. Worldwide efforts to combat the disease by oral vaccination of reservoirs have managed to eradicate wildlife rabies in large areas of central Europe and North-America. Thus, repeated vaccination has been discontinued recently on a geographical scale. However, as rabies has not yet been eradicated globally, a serious risk of re-introduction remains. What is the best spatial design for an emergency vaccination program - particularly if resources are limited? Either, we treat a circular area around the detected case and run the risk of infected hosts leaving the limited control area, because a sufficient immunisation level has not yet been built up. Or, initially concentrate the SAME resources in order to establish a protective ring which is more distant from the infected local area, and which then holds out against the challenge of the approaching epidemic.MethodsWe developed a simulation model to contrast the two strategies for emergency vaccination. The spatial-explicit model is based on fox group home-ranges, which facilitates the simulation of rabies spread to larger areas relevant to management. We used individual-based fox groups to follow up the effects of vaccination in a detailed manner. Thus, regionally - bait distribution orientates itself to standard schemes of oral immunisation programs and locally - baits are assigned to individual foxes.ResultsSurprisingly, putting the controlled area ring-like around the outbreak does not outperform the circular area of the same size centred on the outbreak. Only during the very first baitings, does the ring area result in fewer breakouts. But then as rabies is eliminated within the circle area, the respective ring area fails, due to the non-controlled inner part.We attempt to take advantage of the initially fewer breakouts beyond the ring when applying a mixed strategy. Therefore, after a certain number of baitings, the area under control

BACKGROUND:Rabies is one of the most hazardous zoonoses in the world. Oral mass vaccination has developed into the most effective management method to control fox rabies. The future need to control the disease in large countries (i.e. Eastern Europe and the Americas) forces cost-benefit discussions. The 'Increase bait density' option refers to the usual management assumption that more baits per km2 could compensate for high fox abundance and override the imperfect supply of bait pieces to the individual fox.METHODS:We use a spatial simulation, which combines explicitly fox space use (tessellation polygons) and aeroplane flight lines (straight lines). The number of baits actually falling into each polygon is measured. The manager's strategic options are converted into changes of the resulting bait distribution on the ground. The comparison enables the rating of the options with respect to the management aim (i.e. accessibility of baits).RESULTS:Above 5% (approx. 10%) of all fox groups without any bait (at most 5 baits) relate to the baiting strategy applied in the field (1 km spaced parallel flight lines, 20 baits per km2 distributed) under habitat conditions comparable to middle and western Europe (fox group home-range 1 km2, 2.5 adults; reference strategy).Increasing the bait density on the same flight-line pattern neither reduces the number of under-baited fox group home-ranges, nor improves the management outcome and hence wastes resources. However, reducing the flight line distance provides a more even bait distribution and thus compensates for missed fox groups or extra high fox density.The reference strategy's bait density can be reduced when accounting for the missed fox groups. The management result with the proper strategy is likely the same but with reduced costs.CONCLUSION:There is no overall optimal strategy for the bait distribution in large areas. For major parts of the landscape, the reference strategy will be more competitive. In situations where set

Für die Entwicklung von Managementstrategien in verschiedenen Bereichen der Ökologie bilden oft Raum-Zeit-Daten die wesentliche Grundlage. Deshalb sind Entscheidungsträger auf eine genaue Beschreibung dieser Datensammlungen angewiesen. In der Praxis besteht eine solche Datenbeschreibung aus einer grafischen Darstellung, aus abgeleiteten Hypothesen und einer statistischen Evaluierung dieser Hypothesen. Traditionelle Methoden der grafischen Veranschaulichung von Daten verlangen vorab eine Aggregation der Information. Die Einschränkung überträgt sich dann auf die abschließende Beschreibung. Der vorliegende Artikel illustriert die zusätzliche Unsicherheit, die aus der a-priori Aggregation von Information resultiert. Als Ausweg wird eine moderne Methode der Datenexploration aufgezeigt: Data Movies.Zur Demonstration werden Daten aus einer epidemiologischen Studie zum Vorkommen des Aujeszky Virus im Wildschwein herangezogen. Dabei werden Erkenntnisse aus der Anwendung traditioneller Methoden in der Literatur den Erkenntnissen aus der Anwendung von Data Movies gegenübergestellt. Durch die Visualisierung mittels Data Movies kann erstmals der Verbreitungsprozess des Virus unmittelbar verfolgt werden und zwar simultan in Zeit UND Raum. In der Konsequenz führen neuartige Hypothesen zu einer völlig veränderten gedanklichen Vorstellung über das untersuchte Phänomen. Es wird demonstriert, wieso Data Movies den kompletten Inhalt raum-zeitlicher Daten erfassen und so eine adäquatere Beschreibung der Daten liefern. Schließlich wird verdeutlicht, dass Data Movies mühelos in Publikationen und Präsentationen integriert werden können.

In this study, ecological models, optimisation algorithms and threshold analysis were linked to develop oral-vaccination strategies against rabies in fox populations. It is important that such strategies are cost-efficient and resistant to environmental conditions which would lessen their success.The model validation shows that the ecological models used are suited to predict the proportion of tetracycline- (TC) marked foxes in the course of time. This figure indicates the proportion of foxes which had at least one contact to vaccine baits, and is based on the design of the vaccination strategy (i.e. the number and timing of vaccination campaigns and the number of baits used per square kilometre and campaign). The design of a vaccination strategy also determines the costs.It is the combination of ecological models and optimisation algorithms that helped us to design a vaccination strategy which is capable of achieving a continuous rate of >70% of TC-marked foxes within an analytical horizon of 3 years at low costs. Compared to the standard strategy (baseline comparator), the improved strategy incurs just over half of the cost while almost doubling the number of weeks during which the proportion of TC-marked foxes is >70%.In the improved strategy, June is recommended as the time for bait distribution. The standard strategy, however, avoids summer months (because high temperatures reduce the durability of the baits) which again leads to a reduction of the bait intake by the foxes. Using threshold analysis, we examined the effect of a reduced durability of the baits on the design of the improved vaccination strategy. We concluded that distribution of baits in June was optimal given that the durability of baits is above a threshold of 7 days.

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We used a simulation model to study the spatio-temporal dynamics of a potential rabies outbreak in an immunized fox population after the termination of a long-term, large-scale vaccination program with two campaigns per year one in spring and one in autumn. The `worst-case' scenario of rabies resurgence occurs if rabies has persisted at a low prevalence despite control and has remained undetected by a customary surveillance program or if infected individuals invade to the control area. Even if the termination of a vaccination program entails such a risk of a subsequent new outbreak, prolonged vaccination of a wild host population is expensive and the declining cost-benefit ratio over time eventually makes it uneconomic. Based on the knowledge of the spatio-temporal dynamics of a potential new outbreak gained from our modelling study, we suggest "terminating but observing" to be an appropriate strategy. Simulating the decline of population immunity without revaccination, we found that a new outbreak of rabies should be detected by customary surveillance programs within two years after the termination of the control. The time until detection does not depend on whether vaccination was terminated within the fourth, fifth or sixth years of repeated biannual campaigns. But it is faster if the program was completed with an autumn campaign (because next-year dispersal then occurs after a noticeable decrease in population immunity). Finally, if a rabid fox is detected after terminating vaccination, we determine a rule for defining a circular hazard area based on the simulated spatial spread of rabies. The radius of this area should be increased with the time since the last vaccination campaign. The trade-off between the number of foxes potentially missed by the emergency treatment and the cost for the emergency measures in an enlarged hazard area was found.

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Rabies in the red fox populations of Germany is not yet eradicated by means of vaccination. Lasting incidences are difficult to explain while a reformation of the current disease control is under discussion for economical but also for ecological reasons. Our simulation outcome suggests low-level persistance associated with spatio-temporal moving infection clusters as a potential behaviour of the immunised fox-rabies system. Based on this understanding we explain the lasting incidences and their detection difficulties. We furthermore analyse the temporal dynamic of a potential post-immunisation outbreak based on existing low-level persistence. Because of the obvious clear time horizon of a new outbreak its likely detection by the applied surveillance can be predicted. We recommend to use this insight to prepare more efficient local control strategies to deal with potential new outbreaks instead of prolonging the current large-scale programme.

The large-scale immunization of European fox populations against rabies is currently under the microscope for reducing the considerable expenditure without putting public health at risk. Empirical knowledge is inadequate to interpret the lasting sporadic incidences and, therefore, to verify the final success of the immunization campaigns. By using a proven simulation model we show that rabies can persist on a very low level in the form of spatio-temporal moving infection clusters within a highly immunized fox population. We found further: (i) the existence of a threshold after which the chance of eradicating the disease by vaccination increases clearly and (ii) that at least six years of 70% mean immunization race are required to guarantee a likely success.

Rabies in the red fox populations of Germany is not yet eradicated by means of vaccination. Lasting incidences are difficult to explain while a reformation of the current disease control is under discussion for economical but also for ecological reasons. Our simulation outcome suggests low-level persistance associated with spatio-temporal moving infection clusters as a potential behaviour of the immunised fox-rabies system. Based on this understanding we explain the lasting incidences and their detection difficulties. We furthermore analyse the temporal dynamic of a potential post-immunisation outbreak based on existing low-level persistence. Because of the obvious clear time horizon of a new outbreak its likely detection by the applied surveillance can be predicted. We recommend to use this insight to prepare more efficient local control strategies to deal with potential new outbreaks instead of prolonging the current large-scale programme.