Email from Ruth Watkins to warmwell 22 September 2007
The ITV news sadly stated that the farm where the cows were culled on suspicion has tested positive for FMD the 6th case.
Will this trigger vaccination?
Will a case of bluetongue in the UK trigger FMD vaccination?
Do you think that Brown can call an autumn election without FMD vaccination?
I am not sure where you got your info that virus coated in antibody would test negative on the Pirbrilght lateral flow device test for virus particles. It actually might make it a little more sensitive, a clump of viruses aggregated by antibody might be more easily entrapped. However once antibody is formed and detectable to FMD it signifies there is an effective immune response so that the amount of virus very quickly diminishes in the infected animal.
I would think that sampling old lesions by their penside test is likely to be negative, whilst the PCR test will remain positive. This would not be because of antibody coating but because there is not enough virus present to register positive in the Pirbright lateral flow device.
I think DEFRA should bring its ideas of good diagnostic practice up to date. I agree with Roger Breeze.
Reliance should not be placed upon visual examination in the protection and surveillance zones (which may anyway be not the correct size). Sampling should be done. We have heard nothing of faecal sampling or milk sampling where essentially pooled specimens can be submitted to PCR and culture. Nose swabs and lesion swabs and blood can all have PCR done on them. Again nose swabs can be pooled. This appropriate test is looking for the presence of virus. If there are lesions then the penside test can be done as well. Obviously they have not invested in a. mobile laboratory. Any animal susceptible to FMD should be sampled in this way.
Testing for antibody as in the case of surveillance once the acute infection phase is thought to be over, or in the case of any sheep farms sampled even acutely when there are no clinically diseased animals, is clearly a 'convalescent' test and I believe they are thinking of it as such.
Whilst it is useful to look out for and report clinical signs there is too much emphasis on this at present. Sampling should be done in all cases. It is assumed I think that wherever there is FMD in cattle or pigs it will clinically come to light and be noticed. I suspect myself that seeing ulceration is difficult to notice except perhaps in dairy cattle or penned pigs where one can take a good close look. If there is very gross salivation this may be seen on a field visit but cows do drool a little saliva so it would have to be an excessive amount from a miserable looking animal. The most constant signs, even when ulceration is cryptic, will be an animal off colour, not eating or behaving normally, looking depressed or on its own, not peacefully chewing cud. The most common sign I am sure that vets miss is taking the temperature. I know this is not routinely taken even when assessing a cow for any signs of clinical bovine TB. Unless a doctor is an infectious disease physician they can also make these elementary errors.
Pirbright should be using the most up to date and most rapid diagnositc methods. I am not sure what role DEFRA has in influencing the methods used. Is Pirbright given the responsibility to direct the sampling operations and the funding to put into practice rapid field virology? The DEFRA vets are in the field and I expect they assume the arrogance of the ignorant as they do in bovine TB for example. Few if any DEFRA vet would have any understanding of laboratory diagnostic virology nor any special knowledge of FMD diagnosis.
I think farmers would be doubly mortified if they knew that diagnosis especially in screening was not the best available, in this epidemic of laboratory escapee virus.
DEFRA cannot be in control when they do not know for sure how the virus escaped from the Pirbright site nor how it has reached Egham, with quite a gap in distance and time even if farm 5 was infected about 2 or 3 weeks after farm 2. They should create quite a large vaccination zone, perhaps larger than Surrey depending on natural boundaries especially to deer.
Dr Ruth Watkins BSc Hons, MSc, MBBS, MRCP, MRCPath. e-mail email@example.com is an expert virologist and farmer
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