----- Original Message ----- From: Dr Colin G Fink To: mary critchley Sent: Wednesday, February 14, 2007MaryI have added some clarification for the readers:
Half truths do seem to persist. There are undoubtely logistical difficulties to vaccination in poultry. I think that there is some comfort in the fact that all the outbreaks have been in domestic rather than wild birds. So it is within our power to control these outbreaks if sensible policies are enforced. It is an especial risk in a confined high density flock as we have seen. ( Bit tough on these birds though, that have no real life anyway. But that is a part of the problem- intensive factory methods to produce cheap meat. I do not like that for several reasons, not all virological.)
High density of birds increases the transmission rate of the infection between individuals. If they were all vaccinated , any virus infection introduced would have low flock spread with little if any subsequent shedding into the environment.. The birds would remain clinically well. However no symptoms in the birds together with no understanding by the handlers of even small risk of infection spread outside a flock could lead to some transfer of organisms out of the flock if the biosecurity was not strictly observed. No biological system is ever absolute especially when run by staff who do not understand transfer of infection .
I am not sure what is better for these hapless creatures and their factory bosses in high density rearing. Such a devastating outbreak with much virus shedding as we saw followed by immediate culling or no virus shedding but a minimal risk of ' wild type' viral carriage for short while only?
I am sure that vaccine would break the transmission cycle even in high density flocks. Vaccine for all the smallholders' birds would be very effective in preserving them clinically well and in lower density flocks transfer of wild type virus would be minimal or none. It is theoretically possible to have a small replication of virus in any succesfully vaccinated individual after vaccination. But we do not look because the criterion for successful vaccination is maintenance of good health of the individual and also the failure of 'wildtype' to gain a foothold. What we are concerned about is whether any individual can then act as a vector for the disease. That is very unlikely in a vaccinated flock. Which is the 2nd reason for vaccination .
The Vet lab virologists are producing fine data on the sequences of the viruses and the politicians seem conveniently deaf to the meaning of this.
I believe that the carcase material brought in was infected with H5N1. One way of transfer of this infection so rapidly to the flocks would be If the residue of the carcase meat has been ground up and fed to the new chicks as a high protein feed. That is one way the infection could be transferred into the turkey chick stock. I expect that if they wish to do this they will boil it now.
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