The disease bluetongue requires a number of ingredients: the causative virus, susceptible hosts
(ruminants such as sheep, cattle, goats), clement weather, and a go-between. The latter are midges of
the genus Culicoides. The virus cannot spread by coughs and sneezes, contact or faeces; it must be
injected into the bloodstream of its victims. The 'needle' is provided by female midges (male midges do
not bite - they do not feed). When a midge takes a blood meal from an infected ruminant, virus in the blood
enters the midge, where it replicates in its gut. When the amount of virus is maximal some of it ends up
in the salivary gland of the midge. When it pierces another victim it injects virus along with anti-coagulant.
IAH's entomologists Dr Simon Carpenter and Dr Chris Sanders (light and dark shirts, respectively, in the
pictures below) were filmed by the BBC for a short video on the BBC News website. This shows them catching
midges using a 'truck trap', a large net atop a vehicle. Flying midges and other insects are funnelled into
a collecting pot when the vehicle is driven along. Back in the lab the catch is analysed with regard to the
number and species of the midges caught at different times of the year, at different times of the day and
night. To study the midges that are on sheep, the scientists put sheep from the field into a kind of tent.
The midges fly off to the inside walls of the tent, where they are collected using a mouth-operated 'pooter'.
The
video
can be viewed on the BBC News website, and there is another
video
on the BBSRC website.