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Email from Dr Ruth Watkins 2007 Sept 27

Dear Mary,


I sent this to the editor at Farmer's Guardian and thought you might be
interested.

Dear Mr Davies

I would like to make three points about your article:

(1)  You appear to support the policy of trying to control bluetongue
without vaccination because of a difficulty that you cite on the propensity
of the bluetongue virus to exchange information in the same way as influenza
virus because it has a segmented genome and there are 24 serotypes.  While
the ability to undergo recombination is true in actual fact the only
bluetongue virus in Northern Europe is the serotype 8, therefore there is no
other bluetongue virus that it can recombine with.  Recombination can only
take place when an animal is simultaneously infected with two different
serotypes.  Therefore this cannot happen in Northern Europe.

It is not proposed to use the live vaccine developed for use in Africa
because this is not sufficiently attenuated for european livestock.

It is proposed to use a killed vaccine made by inactivating bluetongue
serotype 8 grown in tissue culture and obtain a license quickly on the basis
that similar vaccines to bluetongue serotypes 2 and 4 that circulate in
Southern Europe have been successful.  We don't have these two viruses in
Northern Europe.  They are confined at present to areas where the Culicoides
imicola midge exists, and this has not yet been able to move into Northern
Europe.

(2)  Indeed the midges implicated in Northern Europe are Culicoides
obsoletus complex and Culicoides dewulfi both of which breed in dung,
cattle, sheep and horse, and are associated with animal housing. That is
thought to be the reason why the epidemic in Europe last year persisted into
December.  A really good freeze is needed to freeze the dung solid in and
around animal housing.   If you look at the bluetongue policy of defra it
acknowledges that housing animals in the case of BTV-8 may not be
recommended. They are housed when ill because exposure to sunshine makes the
illness worse it is thought.  Anyway they are often so ill that they need
supportive therapy such as liquid feeding.

(3)  The killed vaccine will be more expensive to make than a live vaccine
because one has to have so much more virus in each dose of killed vaccine to
elicit an immune response to antigen.  This is in contrast to live vaccine
where only 1000 units of infectivity, infectious virus particles, have to be
used, and if these were killed they would make no impact at all on the
immune system.  The advantage of using live vaccine in Africa is that only
one vaccination for the animal is required (like that to prevent enzootic
abortion in sheep, live C psittaci) rather than boosters annually with a
more expensive vaccine (like heptavac-P plus in sheep).

I strongly suspect there will be limited amounts available as 10s of
millions of animals will need to be vaccinated.  However any animal that has
recovered from the infection will be immune for life and never need
vaccination.  Therefore vaccination of animals born after infection ceases
for the winter should be the priority in the areas afflicted this year|.  In
human medicine it could prove cost effective to screen adult breeding
ruminants before vaccination, particularly if vaccination would be required
on an annual basis to protect animals that have never been infected.

It will be most important to vaccinate all domestic ruminants in
surveillance zones and further out than these to prevent the spread of
BTV-8.  It will be endemic in areas where it occurs at present.  As it
infects wild deer it may be sustained in the face of solid immunity induced
by vaccination in all domestic ruminants for some years to come at least.
It may never be eradicated from Northern Europe in the foreseeable future.

We don't have a vaccine available this year so defra must do what seems
sensible even though we know from experience in Northern Europe the measures
to control midges and reduce biting will not be successful and nor will
animal movement restrictions in preventing the inexorable spread of BTV-8.
We do have enormous numbers of deer in East Anglia and it is probable that
all species of deer can be infected and transmit to midges implicated.

I enjoy reading the Farmer's Guardian and I appreciate this is a new and
complex subject but I would suggest your editor makes sure that what you say
is run past a virologist first.  The team at Pirbright would be glad to help
I am sure or you could ring me and I will guide you where I have the
knowledge.

yours sincerely Ruth
Dr Ruth Watkins, retired consultant virologist.
Ruth Watkins

ruthwatkins@supanet.com

01550740660


 

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

 

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