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Video transcript: Midge-hunting scientists tackle spread of devastating bluetongue virus

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Dr Simon Carpenter, Institute for Animal Health
Bluetongue virus is an arthropod-borne virus, what that means is that it’s transmitted by insects and in this case it’s transmitted by biting midges. These are really tiny flies. If you look at the Culicoides of these midges, they are about the size of an E on a penny, so it’s incredibly small. And these actually transmit the virus and it’s probably the only way the virus is transmitted. And we’re interested in it now because, due to climate change, the virus has been moving up from the Mediterranean basin right up into northern Europe. It arrived in the Netherlands in 2006. Bluetongue virus serotype A is a bit strange in that is also seems to be transmitted also trans-placentally; so it seems to be able to be transmitted from the mother to the young. So this could be why it seems to have managed to overwinter under conditions that would usually have knocked it out of northern populations. During the winter the midges overwinter as larvae and can’t transmit the virus to their offspring, so it has to somehow survive the northern European winter.

The interesting thing as well about bluetongue virus serotype A is although we predicted bluetongue virus could come into the UK at some point, this is actually being transmitted incredibly successfully. It looks like at least one of the species we’re dealing with on the midge side is incredibly competent with the virus and is able to transmit it very easily.

Outside the car…
Today what we’re trying to do when with this rather fine truck-trap is to look at the behaviour of biting midges which spread bluetongue virus, under different meteorological conditions and also at different times of the day. So what we’re doing is running along a path with a truck-trap on top of the truck. What this does is to catch any insects that are flying around in the surface above where we’re driving, and this allows us to look at what insects are flying around under different meteorological conditions. The one we’re interested in is Culicoides biting midges, which is responsible for spreading bluetongue virus, which appeared in the UK late last year. And what we’re trying to find out is whether the meteorological conditions determine what insects you get and in particular the Culicoides midges, so we can advise farmers when they can stable their livestock and various other things. We’re also putting this data into our mathematical models to predict where and when bluetongue will be transmitted and at what times during the year.

Driving along…
At the moment we’re just driving along this route, which basically encompasses a lot of landscapes that midges are present in. We’ve got grazing to our right which is mainly sheep, and we’ll go past a load of calves later on. This gives us a representation of the populations across these environments. The trap is a muslin tent which we put on top of the truck. This is drawn tight so that any insects that go into the trap end up in the back of it and then we collect into a small net at the end of the trap. It collects everything that flies through the trap. And then at the end of the run we’ll take it off and look at what’s in it. Let’s go and have a look…

Car stops…
Chris is going to jump up and remove the net which contains all the insects that we’ve caught during the trapping so far, and then we’re going to put them into a killing jar, which contains chloroform. That will kill all the insects that are in there. Then we’ll sort them out, put them into ethanol and take them back to Pirbright to identify them…

In the tent…
Sheep like these are the worst-affected by bluetongue, so what we do to find out which midges are feeding on these sheep is put them into a large tent….OK so I’m now getting into the tent….OK so I’m looking for midges now. They usually collect up in the corners of the netting…that looks like one there….and I just blow them into the tub like that.

Next to the weather station…
So what we have here is a weather station that is downloading data from the sensors on it, which record things like wind direction and speed, and also temperature and humidity. What we do is to use that data to correlate with truck-trapping and also the drop-trapping to give us an idea of when the midges are active and also what meteorological conditions they’re flying under and biting the sheep.

Back to head shot…
Experiments are vital because it’s knowing your enemy to a certain extent. Then you can put into place things like stabling. We also need to understand how insecticides work and whether they’re going to be effective against these insects. It’s looking at the midges and thinking ‘when are they going to be active and what can we do to put a barrier between our livestock and these midges?’

ENDS