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IT is nearly 10 years since, in the summer of 2006, bluetongue virus serotype 8 (BTV-8) appeared in northern Europe, resulting in more than 2000 cases of bluetongue in that year alone. Its arrival was quite unexpected, and no one knows where it came from. However, its arrival in the UK just over a year later was less of a surprise, as its spread to the UK via infected midges blown on the wind from the Continent had been predicted by epidemiological and meteorological modelling (Gloster and others 2007). In the event, bluetongue did not take off in the UK to anything like the extent that it did elsewhere in Europe, which was largely attributed to the success of a vaccination programme following rapid development and deployment of a BTV-8 vaccine (Burgin and others 2009). Nevertheless, it proved costly and disruptive. Against the background of the 2006-2008 epizootic, a warning from Defra, based on a risk assessment carried out in the light of the recent re-emergence of BTV-8 in France, deserves to be taken seriously.
In a warning issued last week, Defra urged farmers to remain vigilant for bluetongue in 2016, and to monitor their stock carefully. Any signs of the disease should be reported to their vet and the APHA immediately. Its warning followed a risk assessment undertaken by the APHA indicating that the UK is at risk of an outbreak during the spring and summer months, with an outbreak in late summer considered the most likely. This would be the result of infected midges being blown across from France to south-east England.
Defra also advised farmers to speak to their vet about the benefits of vaccinating their animals against bluetongue, based on their locality and individual circumstances, and if they have any concerns about their stock. The risk of disease being introduced as a result of infected midges being blown across from France is, it pointed out, difficult to predict at this stage, as it is highly dependent on the level of disease on the Continent, how close it gets to the UK and the weather, although things might become clearer as the year goes on. Nevertheless, as an approximation, and with a high level of uncertainty, the APHA's risk assessment suggests that the risk of an incursion in a cool spring (with average temperatures below 12°C and 15°C) could be between 5 and 10 per cent; this, it suggests, could rise to between 33 and 60 per cent later in the summer and to between 60 and 80 per cent by the end of the summer.
Bluetongue, Defra pointed out, does not affect people, meat or any other animal products including milk, but can cause illness in both domestic and wild ruminants, including sheep, cattle, goats, deer, llamas and alpacas. The disease is hard to identify but, if suspected, can be rapidly confirmed by diagnostic tests. Information on how to spot the disease in sheep and cattle, along with information on how to report the disease and the control measures that would be applied in the event of an outbreak, is available on the Government's website at www.gov.uk/guidance/bluetongue. An article discussing the differential diagnosis of bluetongue was published in In Practice in 2008 (Williamson and others 2008).
The APHA's risk assessment is well worth reading. It provides a useful reminder of how and when bluetongue might be transmitted as well as what happened during the European epizootic of 2006-2008, while also highlighting the uncertainties about what might happen in 2016. A more detailed overview of the 2006-2008 epizootic was published in an article in In Practice in 2009 (Hateley 2009).
The risk assessment also discusses the role of vaccination and residual herd immunity, as well as movement controls, in helping to reduce disease spread. It suggests that it is likely that immunity is greatly reduced since the last outbreak and that a substantially naive population is now present in Europe.
When BTV-8 arrived in Europe in 2006, efforts to control it were hampered by the fact that a vaccine was not available. This was less of a problem in the UK than in other parts of Europe, as the virus arrived later, a vaccine was being developed and Defra purchased stocks for deployment in advance. With vaccines now available, availability, should, theoretically, be less of a problem in 2016, so it is perhaps worrying that the APHA's risk assessment should remark that, in the current outbreak in France, ‘vaccine supplies are limited and therefore France is targeting animals destined for export, animals moving out of the restriction zone or animals in high value genetic breeding programmes.’ Defra's strategy for controlling bluetongue in Great Britain, which was updated in 2014, indicates that it is unlikely that government would purchase stocks of vaccines for use in an outbreak, but it would seem important to ensure that vaccines are available if the disease looks like taking off.
According the APHA's risk assessment, the Government's bluetongue control strategy ‘confirms that the most appropriate control will be through vaccination, but that this should be an industry-led voluntary action which farmers should choose in consultation with their vets’. This places a responsibility on the industry to be prepared for and try to prevent an outbreak. Defra has contingency plans in place for dealing with notifiable exotic disease outbreaks. Despite the current uncertainty, it will clearly be important to watch out for bluetongue in 2016, and hope that those plans do not have to be put to the test.