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EXECUTIVE SUMMARY
This supplementary report should be read in conjunction with the final report of project CR/2007/56
Bluetongue virus ( BTV) is a significant pathogen of ruminant livestock, carried by midge vectors, that was detected for the first time in England in the autumn of 2007. In recent years, the area affected by BTV has altered significantly with disease occurring in animals across wider parts of mainland Europe and the virus over-wintering in Northern Europe in 2006/2007.
There is a high likelihood that BTV will enter Scotland in the foreseeable future but there is significant uncertainty about many aspects of the disease including a full understanding of how both UK livestock and midge populations will respond to BTV and the effectiveness of existing disease control measures. The possible control measures include vector control, vaccination and movement restrictions combined with surveillance for early detection ( Defra, 2007). However, despite the knowledge gaps there is a need to consider control strategies for Scotland and, prior to implementation, to evaluate their effectiveness in order to prepare for the possible incursion of BTV. Since the relevant biological information is not yet available, or at best is emerging, this report's economic analysis is based on expert knowledge, assumptions about how BTV will behave in Scotland and an integration of the work through epidemiological modelling.
A multidisciplinary expert panel, including BTV and midge experts, agreed a range of feasible BTV incursion scenarios, patterns of disease spread and specific control strategies. Our study was primarily desk based applying quantitative methodologies with existing models, where possible, and data already held by different members of the project team. We explored the most likely distribution of the disease given Scotland's agricultural systems, unique landscape and climate. We engaged with Scottish Government officials and with livestock industry representatives to help inform decision making and prioritisation of disease control options should BTV spread to Scotland.
The project had strict time and financial constraints and therefore had to be restricted to explore a limited number of possible incursion scenarios against a restricted range of control options agreed with Scottish Government ( SG). The range of modelling tools adopted for this research allowed us to pull together the existing data and organise it in the best way to meet the project objectives. The expert panel helped with estimates where data were missing and generally advised upon procedures.
This is an extension of the initial work in order to analyse the economic impacts of an additional response scenario, namely vaccinating 80% of holdings in a protection zone ( PZ) comprising the whole of Scotland. The methodological approach, cost-benefit analysis is identical with the one used for the scenarios analysed in the initial part of the work (see initial BTV report).
1. Development of feasible incursion scenarios (Objective 1)
The incursion scenarios agreed by the expert panel and the SG advisors were: a) northwards spread of infected midges, with BTV arriving in April 2009; b) northwards spread of infected midges, with BTV arriving in July 2008; c) northwards spread of infected midges, with BTV arriving in September 2008; d) import of infected animals in April 2009 and e) import of infected animals in September 2008. The impacts of 5 alternative control (vaccination) strategies within each of these incursion strategies was investigated in the original study. Of these, the one that delivered the lowest mean total outbreak losses under almost all scenarios was option C4: vaccinating 50% of holdings in a PZ comprising the whole of Scotland. The only exception to this was in incursion scenario e (importation of infected animals in September 2008) where the lowest mean total outbreak losses depended on vaccinating according to the location of the outbreak (control option 5). These results raised the question as to whether or not a higher uptake of vaccine in a PZ comprising the whole of Scotland was economically justified. The control strategy analysed in this extension of the initial report is therefore control option C6: vaccinating 80% of holdings in a PZ comprising the whole of Scotland.
2. Economics (Objectives 3 & 4)
In most incursion scenarios control option C6 and C4 give the lowest outbreak losses (least discounted benefits from disease prevention) of all vaccination strategies. The only exception was scenario e where control option C5 was best as observed previously in the main report. It was concluded that no particular advantage or disadvantage was associated with raising uptake of vaccine from 50% to 80% in a PZ for the whole of Scotland. It is assumed that the value of the benefits of the higher rate of vaccination highlighted in the epidemiological results (reduced spatial spread of disease) must have been offset by the greater costs in achieving such increased uptake. In this case and given the uncertainties inherent in this type of ex-ante analysis, targeting the higher rate of vaccine uptake might be considered prudent.
The vaccination strategy results are little affected by variations of up to 5% in the main assumptions, whether or not a licence was available for movement to slaughter and whether the outbreak continued unabated or declined from year 3 to year 5. As regards taking the worst (97.5th percentile) or the best (2.5th percentile) epidemiological predictions, the rankings are similar with the ones obtained in the 'means' predictions. Overall, the robustness is reassuring. However, great uncertainty still surrounds the probability and nature of incursions of BTV into Scotland and the relative economic efficiency of alternative prevention and control options.
The separate potential impacts of BTV incursion on the sheep and cattle sectors were studied using an example (incursion a, control option C6). As was the case for C4 in the initial report, the direct losses due to an outbreak of BTV (mortality, morbidity, vaccination etc.) were greater for sheep than for cattle, these were dwarfed by other direct costs (baseline prevention costs, movement restrictions etc.), which were dominated by cattle associated losses. This result must be emphasised through communication with the Scottish cattle sector.
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