" ...if you can
get ahead of the disease, time is on your side.
On the other hand there is a ground shift going on in Europe to
follow the South American lead and use vaccination, not slaughter, to
control this disease"
Scientists -- and British veterinary authorities involved in
controlling the 2001 foot-and-mouth epidemic -- have known since early
2001 that a real time PCR test can detect cattle, swine, and sheep
infected with foot-and-mouth disease virus 24 to 96 hours before they
show any clinical signs of disease and before foot-and-mouth disease
virus can be isolated from the animals by cell culture ("Use of a
portable real time reverse transcriptase polymerase chain reaction
assay for rapid detection of foot and mouth disease virus," Callahan
JD et al, J Am Vet Med Assoc. 2002; 220(11): 1636-42, 2002; [abstract
available at <http://www.ncbi.nlm.nih.gov/pubmed/12051502]. We have
also known for over a decade that this real time PCR test can be
performed at the site of the potential foot-and-mouth outbreak using
automated PCR analyzers that do not require a laboratory and that
scientific experts located anywhere in the world can follow the PCR
process as it is actually being performed at the site of the outbreak
by logging onto the PCR device via the internet. In recent years
advances in device automation have further simplified the PCR test
procedure such that the technical skill required to perform a state of
the art foot-and-mouth PCR test is far less than that required to bake
a loaf of bread in a kitchen bread machine.
And, of course, no one could argue with the statement that control
measures for foot-and-mouth disease should be properly validated. In
this respect, Dr Woolhouse and his colleagues deserve our
congratulations. He is quoted by Reuters as stating that, "This study
shows that what we thought we knew about foot-and-mouth disease is not
entirely true." What more fitting statement could be the epitaph for
the non-validated mathematical models that were the basis for the
slaughter of millions of uninfected animals and economic hardship for
hundreds of thousands in the countryside in 2001? It has the stark and
direct simplicity of a haiku and should be the motto on the DEFRA T
shirts.
Its quiet yet powerful understatement also brings to mind the words
of Japanese Emperor Hirohito in 1945 -- a sentiment equally applicable
to foot-and-mouth in Britain in 2001 -- "The war situation has
developed not necessarily to Japan's advantage."
--
Roger Breeze
3040 P Street, NW
Washington, DC 20007
USA
[Roger makes an excellent point. Any such tests must be run cow-side.
There is no time for the delays inherent in sending off samples to a
distant laboratory. Just think a minute. There are, say, 10 herds
downwind of a known infected/affected herd. Each has, say 100 cows
plus heifers and calves. At each farm the animals have to be collected
up, bled, released, and samples run. Unless you have 10 test teams, it
is going to be 2-3 days before they have all been run. But some will
have developed lesions by then. And the stress of testing will
probably shorten the incubation period. This testing will tie up a
significant number of the available personnel. Secondly what is the
sensitivity, specificity and positive predictive values of this
testing in case DEFRA, or any other authority, is challenged in court.
Any testing has to be fast and efficient. As Roger indicates we are
getting there. Remember a basic rule: What works in a laboratory
setting seldom works as well in the field.
Way back when, Rolly Tinline and I published a paper on the serial
interval (between outbreaks) using the 1967-68 FMD epidemic data. We
showed that the serial interval between outbreaks is essentially 2
incubation periods. That is, one animal gets infected in the target
herd, and it then has to infect her herd mates before enough virus is
being produced to make that onward downwind trip. See: Hugh-Jones, ME
and RR Tinline 1976: Studies on the 1967-68 foot-and-mouth disease
epidemic: incubation period and herd serial interval. J Hyg (Lond).
1976; 77(2): 141-53 (available at
<http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2129867/). So if you can
get ahead of the disease, time is on your side.
On the other hand there is a ground shift going on in Europe to
follow the South American lead and use vaccination, not slaughter, to
control this disease. - Mod.MHJ]