Email to warmwell September 17 2007 from Dr Colin Fink
The problem is in the way that they are assessing virus excretion and detection in sheep. They are using the criteria 'vireamia' based on tissue culture of live virus from sheep. Tissue culture is slow to show virus growth, (several days) labour intensive and will not detect antibody coated virus which will not grow in tissue culture. The culture is also is susceptible to inhibitors in mucosal samples.
RT- PCR( reverse transcriptase followed by polymerase chain reaction amplification of a virus specific nucleic acid) will detect minute quatities of RNA in virus particles even if they are antibody bound and thus no longer detectable by tissue culture.
RT- PCR is also complete in about an hour and is a whole new level of sensitivity and specificity.
So for diagnostic puposes asking the question " Do these animals carry virus and therefore are they infected?" RT -PCR is a very large scientific step forward. The problem the Vet labs have is that they are still locked into their old criteria of diagnosis which does not fit the newer science of nucleic acid amplification (PCR).
RNA may be degraded reasonably quickly and the specimens taken at the farm should either be analysed there on-site, (as Professor Fred Brown suggested in 2001) or be immediately placed in a substance which stops enzyme degradation of the RNA so the specimens may then be conveyed to a diagnostioc laboratory.
But surely the Vet lab staff must know this?
As Clive Aslet quoted in the Sunday Telegraph before editing out:
" there are no lines of communication between the private sector and the public sector."Alas, there is a pool of information and diagnostic experience here which despite invitation, is not available to them.
As far as the public sector is concerned we are " two amateurs in a garage in Birmingham " to quote a public sector clinical virologist at a scientific meeting. in Atlanta USA.
Just now even such amateurs may be useful.
Dr Colin G Fink
Clinical Virologist & Hon. Senior Lecturer in Biological Sciences University of Warwick
Micropathology Ltd Research and Diagnosis
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