Changes

Classically, the major vector for BTV is ''Culicoides imicola''. This midge is found throughout Africa, the

Classically, the major vector for BTV is ''Culicoides imicola''. This midge is found throughout Africa, the

Middle East, southern Asia, Portugal, Greece, Corsica, Sardinia, Sicily and areas of Italy¹, and its distribution appears to be extending northwards. However, ''C. imicola'' has not yet been demonstrated in the United Kingdom. The ''Culicoides'' species found in the British Isles are ''C. pulicais'' and ''C. obsoletus'', which are also common across central and northern Europe. Knowledge of the distribution of these species in the UK is incomplete, but in general the insects gather where breeding sites and hosts occur in tandem.  

Middle East, southern Asia, Portugal, Greece, Corsica, Sardinia, Sicily and areas of Italy¹, and its distribution appears to be extending northwards. However, ''C. imicola'' has not yet been demonstrated in the United Kingdom. The ''Culicoides'' species found in the British Isles are ''C. pulicais'' and ''C. obsoletus'', which are also common across central and northern Europe. Knowledge of the distribution of these species in the UK is incomplete but the insects tend to gather where breeding sites and hosts occur in tandem, with the highest midge concentrations in areas containing cattle, horses and pigs. Removal of livestock decreases populations of ''Culicoides'' by a factor of 10 to 20¹, but some persist by feeding on wild animals and man. Hill sites have fewer midges as climatic conditions are less favourable, and sheep have a less positive influence on distribution.

Thus, the highest concentrations of C. obsoletus and/or C. pulicaris group midges are

In Britain, studies are ongoing to determine midge distribution, seasonal incidence and the competency of the various ''Culicoides'' species to act as BTV vectors.

found where cattle, horses, pigs and, to a lesser extent, sheep populations are highest.

If domestic animals are removed from a site, over several months the midge

list, species distribution, seasonal incidence and vector competency of the various

species.

===Vector Competency===

===Vector Competency===