email received April 10 2007 from virologist Dr Ruth Watkins
Re: bluetongue policyI completely agree with you, that once bluetongue is detected in an animal over here, (with) all the delays that recognition and diagnosis will take and all the infected but asymptomatic animals or ones with symptoms not correctly attributed, it will already be in midges. They have not worked out how it has got from South Africa to Holland, though it is thought it was an imported animal - I suppose it could be imported midges rather than ones borne on the wind too.
There are a number of midge transporting wind events that can occur from Ostend to Norfolk Kent etc. and if Bluetongue is active again this summer in that area of Europe as is expected, there will be multiple opportunities for it to come over. Should one prohibit all ruminants and cull all deer within 150 km of the English coast? I think that is just about as stupid a suggestion as culling animals in whom the disease is recognised.
We cannot spray and kill all midges either; anyway, midges may be important ecologically and the environment would be contaminated.
Things we might do is to think of strategies to decrease the amplification in midges by treating the ruminants
- vaccinating susceptible domestic ruminants, cattle sheep and goats to prevent or lower viraemia,
- and treating all ruminants on the farm when bluetongue is recognised with ivermectin so that the midges that bite them will die and perhaps an infected generation of midges can be enormously reduced. Perhaps more than one treatment three weeks apart.
As the midges breed in moist soil and manure - not water - one can look at manure storage. Sheep might be better off on the hill rather than in the shed near manure in the evenings and at night as has been recommended. The midges concerned are C obsoletus and C dewulfi and perhaps others. C dewulfi likes cow dung and cattle sheds. Cattle are said to act as a reservoir of infection having viraemia longer than sheep - though even they might become ill with serotype 8 (unlike other serotypes in Europe).
The midges like to bite just above the hoof, though doubtless elsewhere too.
It is not known for certain whether the virus can pass from generation to generation in the midge vertically or not; it is thought not.
Developing an inactivated vaccine for serotype 8 at Meriel is an essential thing to try, to protect against disease at least should infection of the vaccinated ruminant occur.
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