Foot & mouth disease - UK: follow-up diagnostic methods

International Society for Infectious Diseases
<http://www.isid.org>

[1]
Source: Farmersguardian.com, 22 Sep 2006 [edited]
<http://www.farmersguardian.com/story.asp?sectioncode=1&storycode=4600>


U-turn on rapid FMD test - on-the-spot one hour result
-----------------------------------------------
A rapid test for foot-and-mouth disease [FMD]
rejected by MAFF at the height of the 2001
outbreak could be used for future outbreaks in
the UK, Government scientists indicated this week.

The Institute for Animal Health (IAH) is trialing
a diagnostic test that will deliver an
on-the-spot result in under an hour, without
having to wait for results from a laboratory.

Efforts to stop the spread of infection in the
2001 outbreak led to many animals being
slaughtered before the test results were known.

Scientists now say more than 1/3rd of sheep farms
and 23 percent of all livestock premises were
wrongly diagnosed as having foot-and-mouth
disease.

A similar rapid penside test, already developed
in the USA, was offered to the UK during the 2001
outbreak but was rejected by the Government
because it had not been validated in the UK.

John Dobson, from the FMD forum, said: "The lack
of penside tests in 2001 meant that many animals
went untested, other animals became infected
while waiting for the results from test to be
returned, and many animals were slaughtered
unnecessarily because of tests returning false
positives."

However, NFU president at the time, Sir Ben Gill,
said the test had been proved to be rubbish, and
they could not afford to test it at the time of
an outbreak.

The test still needs to be assessed by veterinary
surgeons working with cattle herds, including
further laboratory assessment leading up to
validation.

Even then, there is still no certainty the test
will be used in the UK, as the IAH admitted it
may have difficulty persuading companies to turn
it into a commercially viable product.

An IAH spokesman admitted there was probably not much money in it.

But former National Sheep Association chief
executive John Thorley said the test, which has
been designed to be suitable for sheep, cattle
and pigs was massively important' and would speed
up the effects of any control measures that were
put in place during a foot-and-mouth outbreak.

"It would help to act as a counter to the
commercial reality of the way people and stock
move around the country nowadays," he said.

Mr Thorley said the test would be particularly
useful for the sheep sector, where diagnosis was
difficult because animals often showed few
clinical signs of the disease.

******
[2]
Source: The Scotsman [edited]
< http://news.scotsman.com/uk.cfm?id=1394972006>


Foot-and-mouth slaughter worse than necessary
-----------------------------------------------
The extent of the FMD outbreak in 2001 may not
have been as bad as was feared at the time.

More than 1/3rd of sheep farms and nearly a
quarter of all livestock farms thought to be
affected by the outbreak were disease-free, a
study by the Institute for Animal Health suggests.


******
[3]
Source: The Veterinary Record 159:373-378 (2006) [edited]
<http://veterinaryrecord.bvapublications.com/cgi/content/abstract/159/12/373 >


Comparisons of original laboratory results and
retrospective analysis by real-time reverse
transcriptase-PCR of virological samples
collected from confirmed cases of foot-and-mouth
disease in the UK in 2001.

By: N. P. Ferris, D. P. King, S. M. Reid, A. E. Shaw and G. H. Hutchings.

Abstract

There were 2030 designated cases of
foot-and-mouth disease (FMD) during the course of
the epidemic in the UK in 2001 (including 4 from
Northern Ireland). Samples from 1720 of the
infected premises (IPs) were received in the
laboratory and examined for either the presence
of FMD virus (virological samples from 1421 IPs)
or both FMD virus and antibody (virological and
serological samples from 255 IPs) or antibody
alone (from 44 IPs). The time taken to issue
final diagnostic results ranged from a few hours
in cases in which positive results were obtained
by ELISA on epithelia containing sufficient virus
to be detected, to several days for samples
containing small amounts of virus requiring
amplification through cell culture, negative
samples or samples tested for antibody.

Two subsets of samples were analyzed
retrospectively by real-time reverse
transcriptase-PCR (RT-PCR); 1st, epithelia that
were negative by both ELISA and virus isolation
(VI) in cell culture, and secondly, samples that
were negative by ELISA on epithelial suspension
but positive by VI. There was broad agreement
between the RT-PCR and VI/ELISA combined, except
that the RT-PCR procedure did not detect a group
of related virus isolates from Wales. These
viruses had evidently evolved during the epidemic
and had a nucleotide substitution in the RT-PCR
probe site, which prevented them from being
detected by the routine diagnostic probe. No
evidence of FMD virus, antibody or nucleic acid
was found in approximately 23 percent (390 of
1730) of IPs from which samples were received,
suggesting that the incidence of FMD during the
outbreak may have been over-reported.

The over-reporting of FMDV cases occurred due to
diagnosis of disease on symptomatic assessment
alone prior to completion of laboratory
diagnostic tests. The tests (ELISA, Vi and
RT-PCR) were in broad agreement. Although RT-PCR
proved to be the most sensitive, an inadequacy
was revealed in that some viruses (probably) had
mutations in the primer-complementary sites and
some false negative results were generated.

It is an inherent weakness of RT-PCR diagnostic
tests, especially for viruses like FMDV with
small genomes, that the primers used may be too
specific to amplify all variants generated during
virus replication, and false negatives will be
recorded. (Careful design of primer sequences is
an essential requirement in the design of real
time RT-PCR tests).