Thanks to a timely question from Gary in Kansas to Dr Ruth Watkins on the Farmtalking Forum, Ruth has replied with her usual succinct knowledge and understanding. Dr Watkins is not only an experienced virologist but also now a farmer in her own right and has farming relatives who own at least one Bluetongue infected cow.
I wonder if I should send you the whole thing again?
"Ideally the ruminants should be vaccinated in the winter.
Pregnant animals should have the inactivated vaccine. There is plenty of evidence that many modified live vaccine (MLV) for BTV serotypes infect the foetus and cause foetal loss and abnormality. In fact all ruminants can safely be given the inactivated vaccine. Even very young ruminants; it may well be possible to give the vaccine near birth or within 2 weeks of birth. Normally young animals and humans respond well to inactivated vaccine even in the presence of some maternal antibody.
If a modified live vacccine (MLV) was available this could be used for non-pregnant animals and if properly made up and promptly administered the animals recieving the live vaccine should never need another dose re the serotype of BTV they were vaccinated against. The others who had the inactivated vaccine would need an annual booster (you could not easily switch to a live vaccine booster as trace amounts of antibody from the inactivated vaccine would neutralise the tiny amount of inoculating live vaccine virus in the MLV so that the vaccine would not work).
We will only have vaccine available next summer, 2008. In 2009 there should be ample vaccine ready so that vaccination can be done in the winter of 2009.
The effect of starting vaccination next summer in June for instance, to be optimistic, will be only partial in the prevention of spread and make no difference to the re-emergence of BTV-8 infection.
The time line is that it will be the end of June before the vaccinated ruminants are protected. The infected female midges generated during June will be able to spread the infection to any unvaccinated susceptible animals in July, including those outside the vaccination area (in the UK it is rumoured vaccination will start in the protection zone). As it will be a voluntary vaccination there will be a relatively large number of susceptible animals even within the protection zone; even if a farmer vaccinates his cattle and adult sheep will he vaccinate his lambs? Wild deer? Those infected female midges generated in July will ba able to infect any pockets of susceptible ruminants in the protection zone and of course be spreading, by flight or on the breeze, in all directions the infection much more widely in August. The vaccination proposed will be a partial catch-up and may make little difference to spread next summer. So it will proceed through September, October and November.
I can't give any accurate figures on midge survival and re-emergence I feel that entomology experts in the UK should be able to give some idea for our species involved with BTV transmission, C dewulfi and C obsoletus. There were plenty of female midges in April 2007, you can look at the European epidemiology published April 2007 by efsa referenced on farmtalking and warmwell. Obviously in the UK not all female midges generated in November are sure to be dead even now, it has been so mild, in association with cattle sheds and the warmth of cattle, and they may live longer in cool weather than hot. I suspect that spread is still occurring on farms that have infected cattle in particular. My sister's herd is having PCR testing by Micropathology Ltd UK- the 12 adult cows and 3 bulls, to see how many in addition to Duchess have been infected. Some have had mild symptoms suggesting that infection occurred in December and even early January. No surprise if you look at those European epidemiology results published by efsa.
As Osinga and others have suggested, it may be more effective to apply limited vaccine summer 2008 in the surveillance zone to prevent spread. However particularly in the UK the animals in the protection zone will suffer very much and so this has not met with any general approval. The meeting on Jan 16th seemed to be as chaotic and ineffectual as previously. There seem to be no veterinary clinical virologists who have generated plans for vaccination that can be looked at and adopted. There are politicos and research scientists and none in between. I wonder what will happen by 31st of January?"