Email from Nick Clayton, Hon Sec The Goat Veterinary Society. November 22 2008
First of all, thankyou for the kind words re the GVS.
I have been asked to comment further on the "Flower" theory re BTV transmission.
I am only a retired mixed practice man, so I am not an expert epidemiologist. What became clear early in the BTV8 outbreak was how little we knew about BTV, when up to then, I think we thought we knew it all!!
Due thanks MUST be given to researchers at Pirbright, who have done a fantastic job in unwravelling the conundrums that the appearance of BTV in Europe posed. Things move so fast that whatever any of us say at any time, is likely to be superceded within a few days!
When BTV8 first arrived in Maastrichte, my instinct was to think that the obvious new connection was the International Horse show in late May 2006. Could it, I thought, have crept in via midges on horse dung of the three horses at that show from the only known region affected with BTV? That is still not impossible!. However it has become highly improbable.
The talk by Anthony Wilson, a specialist Epidemiologist from Pirbright, at GVS on Thursday, was highly illuminating.
When BTV6 was first reported in Holland, it was thought "almost certainly", to be a live vaccine strain that had "escaped" - as can happen with live bluetongue vaccine. That theory was based on the closeness of the DNA typing of the strain to the one used in multivalent live vaccines in several parts of the world. The argument against that is that none of the other strains in the relevant vaccine had been found on surveillance.
According to Anthony, over the last few days, it is now thought that in fact the strain of BTV6 found in Holland and Germany,is a natural strain, imported from abroad. That has two implications. Firstly it could overwinter, as did BTV8 in 2006/7, and secondly, how did it get there.
The common factor between the "import" of BTV8 and BTV6 is that virus carrying midges could have been imported with flowers from regions known to be infected with those strains of BTV, which are known to circulate where the flowers came from. Unless a more likely scenario emerges, that is as they say, the perceived wisdom. It has been an interesting story.
The discovery of Toggenburg Orbivirus is interesting, but Anthony suggested that this may be a virus which is in wide circulation, with little or no clinical significance. If surveillance proves that that is the case, we can dismiss it as interesting but unimportant.
It is as yet not officially dubbed BTV 25. It occurs to me that if the disease is of no clinical, welfare, or financial importance, it would be unwise to call it anything that includes the word BLUETONGUE, otherwise, detection of it will result in all the restrictions that apply when other, clinically important strains, are found, and for no good reason whatsoever!
I hope you find this useful,
Nick Clayton Hon Sec The Goat Veterinary Society.