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2. EXECUTIVE SUMMARY
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.
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 July 2008; b) northwards spread of infected midges, with BTV arriving in September 2008; c) northwards spread of infected midges, with BTV arriving in April 2009; d) import of infected animals in September 2008; and e) import of infected animals in April 2009. Subsequently, a limited range of control strategies was agreed with Scottish Government. Where possible the impact of the following control strategies was investigated: 1) implementing only the minimal requirements; 2) vaccinating 100% of holdings in a border protection zone ( PZ); 3) vaccinating 80% of holdings in a PZ to the Highland Boundary Fault (B/F) line; 4) vaccinating 50% of holdings in a PZ comprising the whole of Scotland and 5) vaccinating 80% of holdings in a 100km PZ around the first identified holding (only applied if the incursion occurs above the Highland B/F line). (A supplementary technical report was produced in June 2008 to include an additional control strategy that involved vaccinating 80% of holdings in a PZ comprising the whole of Scotland.)
2. Development of epidemiological scenarios (Objective 2)
The epidemiological outputs indicated that for most scenarios infection seldom spreads after the initial incursion; only if an incursion occurred via northwards spread in July did outbreaks become more widespread in a substantial number of replicates. If it goes undetected, an import of infected animals is likely to result in large-scale outbreak, regardless of the time of the year when the import occurs. For all incursion scenarios vaccination is efficient at controlling the spread of BTV and widespread outbreaks will usually be prevented in areas using barrier vaccination with high levels (>80%) of vaccine uptake by farms. If random importation occurs then a higher level of spatial coverage at a lower level of vaccine uptake by farmers (assuming this was evenly distributed through the livestock population) is usually effective for disease control. Vaccination also has a marked impact on the longer-term dynamics of BTV. Infection typically dies out within two years if vaccination is used, whereas it persists if only minimal control measures are applied. (It is important to note that 100% efficacy of the vaccine was assumed in the absence of alternative data).
The analysis of Scottish vector data generated maps of suitable habitat for the bog-heathland Scottish biting midge Culicoides impunctatus. The northern uplands are at high risk of supporting large C. impunctatus populations. The Scottish biting midge is most likely to overlap with farmland, and with domestic ruminants and farm associated vectors in the North West Highlands, along the Great Glen at the foot of the Grampians, and in the Borders. Domestic ruminants overlap with large red deer populations on the Cairngorm plateau, along the Moray coast and sporadically through Highland areas. It is not yet possible to predict how the numbers of farm-associated midge vectors ( C. obsoletus or C. pulicaris complexes) vary across Scotland on the basis of current vector surveillance data, but we outline a future framework for such predictions.
Our knowledge and information base for bluetongue infection is increasing all the time and new information is placed in ANNEX 5. The project call required a restricted focus to BTV serotype 8 however the UK should now be considered at risk from other strains of BTV and vaccination to BTV 8 will not necessarily protect against other strains such as BTV 1 that may reach UK soon. This is discussed in ANNEX 5 (a) with revised information about changes in the currently available tests and the GB capability to provide accurate test results in the face of widespread BTV8 disease provided in ANNEX 5 (b). During the last weeks of the project evidence for the risk of horizontal and vertical transmission of BTV came to light. The economic modelling does not incorporate all this information at this time but it is vital that this emerging information is taken into account when making decisions about how best to control bluetongue in Scotland ANNEX 5 (c).
3. Economics (Objectives 3 & 4)
The objectives of the economic aspects of the work were two fold:
- To develop an economic consequences model for identifying, measuring and valuing direct and indirect socio-economic consequences (costs due to disease control and other consequences) of the virus spreading to Scotland.
- To conduct, under each of the incursion scenarios, an economic evaluation of the strategies available for controlling the disease.
We have based our economic consequences model on the benefits of avoiding the direct and indirect costs of incursion of BTV into Scotland through current (baseline) costs of surveillance and other related activities aimed at reducing the risk of incursion and/or limiting the damage of any incursion. Baseline costs are estimated to be £141m in present value terms over the 5-year time horizon considered.
It is not possible to estimate the probability of each incursion scenario evaluated and these scenarios are in any case just a few of many possible incursions that are not mutually exclusive. This meant that BTV outbreak control options were compared within the specific incursion scenarios.
Benefits of avoiding disease incursion exceeded current baseline costs of prevention in all scenarios evaluated suggesting that the baseline costs are justified. However, without more information about the effectiveness of baseline costs in each scenario it was not possible to investigate this aspect in more detail.
Of the vaccination strategies evaluated, the one that delivered the lowest mean total outbreak losses under almost all scenarios was option 4: 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 depend on vaccinating according to the location of the outbreak (control option 5). The highest mean total outbreak losses are always associated with option 2 (vaccinating 100% of holdings in a border PZ). Under some circumstances, the no vaccination option (1) delivered the lowest mean total outbreak losses. However, given the uncertainties surrounding the probabilities for each incursion scenario and the relatively small differences between the vaccination options, this did not give strong evidence against control by vaccination.
The vaccination strategy results are little affected by variations of up to 5% in the main assumptions, taking worst (95th percentile) or best (5th percentile) epidemiological predictions, 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. This 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 4). Although direct losses due to an outbreak of BTV (mortality, morbidity, vaccination etc.) were greater for sheep than 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.
Direct costs were comparable with recently published estimates from the BTV epidemics in the Netherlands (about £30m per annum). However, direct costs were much smaller than indirect costs (loss of markets, price effects etc.). Although indirect costs are difficult to estimate, our results suggest that they may exceed £70m per annum, reinforcing the importance of investment in baseline costs that reduce the risk and extent of any incursion. (Indirect cost estimates were dominated by reduced demand for beef and hence lower beef prices. The extent of this effect will depend on consumer reaction to news of a BTV outbreak in Scotland. This is very difficult to predict but was assumed to be small at -£0.25/kg (no public health implications). However, a small reaction is magnified by the sensitivity of the beef price to demand change (elasticity) and the large quantity of beef produced in Scotland.) In our study the extreme epidemiological outputs made little difference to the economic assessment of alternative incursion control options based on average epidemiological outcomes. This combined with the results of the sensitivity analysis and the consistency between incursion scenarios is reassuring as it suggests that choice of best control option is robust to the nature and extent of the incursion.
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