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Guidance on the disease vector and potential mitigation measures
The following guidance provides information on the vectors that spread Bluetongue and the mitigation measures that may be appropriate for some situations. Farmers and veterinarians may wish to consider the following advice.
The Culicoides Midge
The Bluetongue virus is spread by Culicoides species of midge.
There are 47 different species of Culicoides but only a few species are able to carry the virus. Some of these species are present throughout the UK. The risk of virus transmission is related to the number of midges present.
Culicoides behaviour
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Populations fluctuate, and peak in May/June and September/October.
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Daily activity peaks at dusk/dawn.
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Some of the most widespread UK species breed around animal dung.
Culicoides mitigation measures
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No insecticides are authorised specifically to act against Culicoides
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Deltamethrin-based compounds have performed best in tests, however, they only offer limited coverage of animals and provide 1-2 days protection at best.
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Generic repellents are only effective for a few hours at best.
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Because they do not entirely remove the risk of an animal contracting bluetongue and their short period of protection, in addition to economic and environmental considerations, the Scottish Government does not advise insecticide use against Culicoides on farms as a practical and cost-effective control measure against Bluetongue.
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Although the Scottish Government does not advise the use of insecticides as a control measure, it supports it application for short-term protection of animals transiting through BTV restricted zones. Animals and their vehicle must be sprayed prior to travel.
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However, in the event of an outbreak insecticide treatments may be required for certain specific livestock movements.
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Any insecticides should be used in accordance with the manufacturers instructions.
Culicoides breeding sites can be potentially reduced by:
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Moving dung heaps away from livestock (>50m where possible), or covering heaps with a plastic, watertight cover.
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Scrape the perimeters of heaps/slurry pits regularly to a depth of 6-10cms (where the majority of larvae reside).
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Housing of animals in an enclosed space (where the means are available to close doors, and cover entrances with mesh) during peak periods of Culicoides activity may reduce biting rates to a greater or lesser extent,
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No one measure will prevent midges biting animals. However, the use of a combination of the measures listed above will sequentially reduce the risk of midge bites and hence reduce the risk animals becoming infected with BTV.
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