"Clearly, it is acceptable to prevent BTV-8 infection the consequences of which can be so awful for the animal and cause so much suffering."email received from Ruth Watkins May 2008
I feel the DEFRA recommendation of not vaccinating animals less than one month old is ill thought through and irresponsible with regard to disease control. DEFRA give no explanation for their recommendation.
If for next year 2009 all ewes and cows are vaccinated during the winter then it would be appropriate to recommend vaccination at one month of age as the young will have imbibed antibodies to BTV-8 in colostrum. One might think DEFRA has said this because the very young cannot respond to killed vaccine but that is not the case.
At birth the immune system is competent and the animal, including the human, is well able to respond to a killed vaccine. Obviously in the UK almost no young ruminants will be exposed to protective antibodies in the colostrum so that they will be fully susceptible to BTV-8 infection from birth. Our vaccination campaign falls during the season when the female midge is actively reproductive and taking blood meals so if farms herds and flocks are to be fully protected and the spread of the BTV-8 virus controlled it is essential that all the animals on a farm are rendered immune by vaccination (wild deer and farms that do not vaccinate will constitute the susceptible 20% so that all vaccinating farms must constitute the 80% immunity that is needed to control the spread of BTV-8 thus they must ensure all their ruminants are immune).
Also it is difficult for the farmer to keep gathering and sorting different groups of animals for vaccination at set times so it is best if possible to vaccinate all the animals at the same time (it may take several days). Marking vaccinated lambs and sorting them from unvaccinated lambs to vaccinate the unvaccinated lambs on a later date is time consuming and unnecessarily complicated. On farms there may be 2 lambs to every ewe and all cows will have young calves and these may be born outside in the summer or during the autumn, not just in early spring. The number of young animals is enormous perhaps more than half of the total number of domestic ruminants on a farm.
As you know, I am careful not to make recommendations to do things unless it is likely to be useful and safe; I was very cautious about midge repellents and I think that has been proven to be the right line to take.
There is no reason to suppose the vaccine is toxic to the very young of the species because it has been shown to be safe and efficaceous from one month of age. The adjuvant in the vaccine may induce a fever or a sterile abscess but this could occur in any vaccinee - and clearly it is acceptable to prevent BTV-8 infection the consequences of which can be so awful for the animal and cause so much suffering.
Paul van Aarle can only confirm what I fear, that is the time constraints and finance have made tests on calves and lambs less than one month of age impossible to do.
It is right that farmers be informed that the vaccine has not been tested on lambs or calves less than one month but they should go ahead and vaccinate these young animals as the vaccine can be expected to work and they need to ensure near enough to 100% immunity to BTV-8 in their flocks and herds. There is no reason to suppose the vaccine would be unsafe in lambs and calves as the vaccine has been tested and licensed for these species from one month old.
Dr Chris Oura (Pirbright) has confirmed that the reason for the 'under one month of age' exclusion is because it is probable the vaccine has not been tested under one month of age - hence my email to Paul van Aarle at Intervet to confirm this. Also Chris Oura confirmed that the animals could be expected to respond well to vaccine from birth and agreed with me that almost all young animals would get no protective antibody against BTV-8 in their colostrum in the UK this year.
I was waiting for Paul van Aarle's reply because I suspect that in the speed to make the BTV-8 vaccine available the experimental work to check that the vaccine is efficacious in vaccination of animals less than one month old has not been done. Indeed it would not be necessary for N Europe where the disease has had such a high prevalence that most young will have passive antibodies derived from colostrum so it would be appropriate to start vaccination at one month of age. There would be a window for the farmers convenience of between one month and about 3 months of age when the waning of the colostral antibodies could be expected to be significant.
In the case of camelids, goats, deer and buffalo (I think this comprises the other ruminant species that may be on farms) where DEFRA recommends the vaccine off-licence should be given by a vet, DEFRA should offer some antibody testing to those owners willing to cooperate to gain field experience of the vaccine's usefulness in these species. These species are not on the license for safety so the BVA suggests quite rightly that any adverse reactions are reported by the vets, and these should include non-response to vaccine, so antibody testing is required at least in some individuals of these species.
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