THE GOAT VETERINARY SOCIETY |
||||
 |
||||
 |
|
|
|
|
|
||||||||||||||
|
|
|
||||||||||||
BLUETONGUE UPDATE July 2nd.
No, Nothing very earth shattering, but I went yesterday to a Bluetongue workshop organised by Intervet Schering plough with a very international panel of speakers, so here, rather disjointedly are some of the main points that came out. The whole meeting has been videoed and will be available as a webcast in due course.
A trial has been carried out in SHEEP where they were given BTV8 vaccine at the same time as Heptavac P, 3 weeks before lambing, and also for another group, 3 and 6 weeks before lambing. In both cases colostral antibody was still strong at 14 weeks of age. Further trials then indicated that vaccination take in lambs is NOT affected by the presence of maternal antibody.
This demonstrates that BTV vaccine can be given at the same time as a clostridial vaccine, and indeed I understand that it is now accepted that in both sheep and cattle a number of vaccines can be used at the same time as BTV8 vaccine without affecting the efficacy of either. I will let you know the full list in due course. However in GOATS the work has not been replicated, and I will take advice from the manufacturers on that point. In the meantime, given the comparitively poor ability of goats to respond to several vaccines, it would seem sensible to follow the not within 2 weeks of another vaccine rule wherever possible until or unless it is proven not to be needed.
Chris Oura from Pirbright, spoke on mechanisms of transmission, including trans placental transmission. One of his points was re- importing animals from areas still heavily infected with BTV. His advice is that animals should have been vaccinated, with the vaccination having been completed at least 60 days before the imports are made, AND, just as important, that vaccination of any pregnant animals should have been completed, at least 3 weeks before service. This was particularly important in summer weather when virus replication could overtake the wait for tests.
The new rules introduced by DEFRA are that when animals are imported to the UK, they should have a PCR test within 48 hours of arrival, and another 7 days later to pick up possible cases incubating the disease at the time of test one. There has been a written commons answer on Wednesday to a question by Baroness Byford as to whether the government proposed to ban imports of ruminants from the EU PZ. Lord Davies of Oldham,( an area famous for agriculture?), replied on behalf of DEFRA that the risk from importing livestock from other EU states was very low, and there had been no import positives since December 2008.
Er, what a surprise, This virus is seasonal M’lud.
He went on to say that “We have a robust post-import testing regime”. Chris, on being asked if the current import policy was sufficient, pointed out that there was still time for midges to bite infected animals before they were blood tested, and before either result became available. That was not entirely to denigrate the dual PCR testing, but in fairness to point out that since that policy came in in March, things have moved on, and I have revised my personal thinking, where at the time I thought the policy WAS a good one, to a feeling that what is needed is a combination of that policy and the vaccination regime Chris thinks should be in place.
When it comes to goats we still have the stumbling block to movement that vaccination in goats is not recognised as there is no caprine MA for any vaccine. What is odd is that the licenses for moving ruminant livestock from within a PZ have suddenly vanished from the DEFRA website. I will follow this up, as without that page, we have no way of guiding anybody anywhere.
One of the reasons for Chris Oura taking his standpoint is that we now know more about transplacental transmission of disease than we did even 3 months ago, and this was backed up by a presentation by Linda van Wuiijckhuise from Holland, who has been involved in similar work.
It is now known that embryos whose dams are infected early in pregnancy, tend to be aborted early. Those infected in the last 3 months of pregnancy tend to be unaffected, or relatively so. It is the ones in the middle that are interesting. they can survive to full term, and while some may be stillborn, many will live, but have the condition called hydroanencephaly, where the cerebral hemispheres are replaced by fluid, leaving them as Chris called it, “Intellectually challenged”, and as Linda called them, “Dummy calves”. They can suck, but not for long, are strong candidates for stomach tubing with colostrum, and then display the characteristics of the bovine equivalent of having in present parlance”Learning Difficulties”. I think we can assume that this might apply to lambs and kids as well, but to what extent we do not as yet know.
What seems to be happening is that these calves are born potentially viraemic, and again here read lambs, and probably kids as well. If they get a good feed of colostrum, whether naturally or by stomach tubing, the virus rapidly disappears, and thus the new arrival is NOT a threat to virus circulation in midges in most if not very nearly all cases. The neonatal that might be a threat is the one who failed to get colostrum, and could therefore be inadvertantly targetted by midges, for as long as it survived, which can be quite a variable time.
Importantly, if these neonates, infected during pregancy, receive colostrum, the disease seems not to progress and not to be a threat, other than transiently to causing circulation of virus in the local midge population. It is those few who are born viraemic, and who did NOT receive colostrum, that could potentially lead to virus circulation.
The possible mechanisms for “Overwintering” of virus were discussed, and while translplacental transmission is still an obvious method, the possibility of what might be called virus hibernation in non ruminant species cannot be ruled out. I think that shows that ths is a disease where we are still learning fast. It is essential that all involved, including politicians, accept that as we advance scientific frontiers we need to adapt to the implications, whether as Scientists, politicians, AH personell, or even secretaries of the various breed veterinary societies in the UK and elsewhere.
This is a debate which is still open, and another possible mechanism of transmission, Oral transmission, is under investigation.
It was fascinating to hear a presentaion form Proffessor James Machlaclan, who has worked on BTV within the University of California, for 30 years. As he said, in Europe we have had ten incursions of Bluetongue in the last ten years. In the USA the have had TWELVE, albeit mainly in the Gulf, IE Eastern, states. James was asked about eradication, and gave the fascinating opinion that in the USA, where disease had been eradicated on a state by state basis, it was usually when only one strain of BTV was involved. Where two or more strains were involved, it became a lot more difficult. BTV8 seems to be one of the most virulent strains known, especially in cattle.
That situation is very close to us. The French Authorites claim to have had a successful campaign of vaccination during the spring of 2009, but that varies from some reports in the field, which suggest that a lot of farmers have only vaccinated their young stock against BTV8 on the distinctly doubtful principle that the older ones probably immuised themselves last year. It is interesting to note that while the sales of BTV1 vaccine in France appear to be close to the number of livestock that can be targetted, sales of BTV8 vaccine are running at only half of that level, though of course a lot of cattle will only have needed 1 dosed this year rather than two. The main concern seems to be widespread failure to vaccinate sheep again.
Herge Petit, all of about five foot one!, presented the results of a study at Linsitut De elevage in France, on the economic effects on farms affected in France as a result of BTV in 2007. 2008 information is still being collated. Costs such as production loss, deaths, veterinary fees etc were all included in the study, in which he subdivided the herds studied into mildly, moderately, and severely infected, though without stating the details of the criteria. Suffice it to say that he calculated the reduction in gross margin in Dairy units as being 1.1%, 6.6% and 8% respectively. In beef suckler herds these figures rose to 6.1%, 8% and 17.7% respectively. For sheep the effects were dramatic. Only a 4% reduction in mildly affected flocks, but 50% in moderately affected flocks, and
106% in severely affected flocks.
It was interesting to note that a far greater percentage of bulls were affected than cows, but this may have been a statistical quirk of a small sample.. There was a report on fertility in affected rams in Holland in 2007, which is interesting in that affected rams produce substandard sperm after getting the disease, but recover normal production by 60 to 140 days after. That however tends to mean missing a breeding season as the timings work out. We have as yet no figures for bulls, and have to assume that Bucks would behave as rams!!. Some seropositive or PCR positive rams that had shown no outward signs of disese became temporarily infertile.
2009 DISEASE SITUATION
Only reports of disease so far are from France where so far this year there have been 14 holdings poitive to BTV8 and 30 to BTV1, though some of those may be surveillance cases picking up a remnant of last year’s infection.
A SOBERING STATISTIC. In Belgium in 2007 27% of the national sheep flock was infected, and of those 40% died.
OTHER POINTS. The Q & A sessions
Chris Oura suggested that eradication would only be achieved after a HIGH level uptake of vaccine for at least 3 or 4 years. A level of vaccine below 60% will lead to infection being present for many years. Current uptake in the UK not known, but isapparently higher in the south and east than elsewhere. Weather conditions right for the last week to lead to rapid spread of and multiplication of, BTV, a weather scenario that never really happened here last year.
The number of calves born in France so far this year is 20% lower than at the same time last year. If replicated worldwide that would have huge food security implications.
In Holland, the prevelance of BTV in cattle that were housed all year round was considerably lower than in cattle kept wholly ot partly outdoors.
The effectiveness of insecticides was variable. Better in cows than sheep, and better in sheep as a dip than as a spray. Problem in sheep was that the dip will not adhere to the midge feeding areas. At best a mitigation measure, not a control measure. Keeping dung heaps away from cowshed doors, and grazing areas, was a bigger help in reducing the numbers of midges available to bite cattle.
Thanks To Intervet Schering Plough for orgaising a very useful update. The underlying theme might be “We know a lot more than we did, but not as much as we would like to”.
Further changes in policy abd recommendations on various aspects of BTV control are inevitable.
Nick Clayton.
BLUETONGUE UPDATE July 2nd.
I went yesterday to a Bluetongue workshop organised by Intervet Schering Plough with an international panel of speakers, so here, rather disjointedly are some of the main points that came out. The whole meeting has been videoed and will be available as a webcast in due course.
You may either follow the links below or click to download the entire 5-page reportHERE
Vaccination Transmission Transplacental Eradication Current situation