2. Although the Bluetongue vaccine we shall have Intervet is not a 'marker' vaccine, it is a very good vaccine and is likely to provide complete immunization from the disease if administered as recommended with regular booster doses. 

3. On an Elisa test the vaccinated livestock would show antibodies to the virus. (But of course no animals have been vaccinated against BT8 in Europe, yet!). 

4. Animals that have had the disease and recovered will be immune for life. (According to Chris Oura, Pirbright). On an Elisa test, they will show antibodies to the virus and may also show virus for some time, but as I understand it, not enough to infect any midges, because the virus is sequestered in red blood cells. It is detectable for some months after infectivity to midges has ceased. 
I understand that for BTV the virus must exit the cell in its normal manner to become infectious so sequestered viruses are not likely to be infectious. It is simply a result of the virus infecting young red blood cells in the marrow. 
Therefore, it is unnecessary to destroy the animals. 
If they remain in a flock or herd and are vaccinated or given a booster dose when their companion animals are, it will do no harm and simply boost their immunity too 

5. It seems that animals tested clear prior to export have tested differently after arrival. 
That is perhaps because they were bitten by a midge(s) and infected after the initial test and have made a subsequent recovery. 
They have produced antibodies and yet still show some virus on test after arrival. 
The fact is, that many infected animals do not become ill at all. It should also be remembered that sometimes no symptoms are evident, especially in cattle, so the disease may not have been noticed, either before they left their country of origin or after arrival at their destination, but they may still be infectious to midges. 
Unfortunately there is no PCR test to determine whether an animal is infectious or not but if it has antibody but no virus on PCR test then it can't be infectious. 
All this assumes that the tests were an are done correctly on animals that were and are identified correctly. 
We know mistakes can be made in identification. 
Obviously the precautions taken to keep the animals free of exposure to midges has failed in some cases. 

6. As the virus is in the blood, the young born to imported pregnant animals, who have had the infection and recovered so that they are antibody positive but no longer virus positive, could have been infected in the uterus during gestation. 
On testing, these live offspring will show antibodies and virus if they were infected in utero. 
Unfortunately such congenitally infected calves (or lambs, etc.) are likely to be infectious for some period of time, a period as yet unknown but could be for a year or more.
They should be purchased for study by Pirbright in preference to slaughter.
A congenitally infected animal with a prolonged infectivity could be a source of over-wintered virus in an infected area in the UK. There will probably be many such young born this winter/spring in the PZ but there is no need to kill them unless they are in an area free of infection before we get the vaccine.

Imported animals and/or those born to them, as described in 5 and 6 above, have been found outside the surveillance zone and have to date, been destroyed by Governments in England, Scotland and Ireland.

Jane Barribal - 2nd March 2008