3 Atypical results
10. The method used to test for Diarrhetic Shellfish
Poisoning (DSP) in the United Kingdom is the Mouse Bioassay (MBA),[10]
whereby shellfish extract is injected into mice. European legislation
established the MBA as the reference test for DSP, that is other
methods are allowed provided that they are as effective as MBA
and where there are discrepancies between the results of different
tests, the MBA result is definitive.[11]
EU Decision 2002/225 stipulates that if two of three test mice
die within 24 hours of the injection, the shellfish sample is
deemed to be positive for DSP.[12]
Aside from the atypical results that are the main subject of this
report, we have some concerns about the mouse bioassay itself,
which will be discussed in greater detail later in the report.
11. Since June 2001, atypical results have been recorded
for shellfish (mainly cockles) being tested for DSP with the mouse
bioassay.[13] Although
the symptoms and speed of death in the atypical results differed
from normal positive DSP results, the mice nevertheless died within
the period set out by the Directive and therefore the FSA is of
the view that the atypical results were positive DSP results as
defined by European Union law.[14]
12. The atypical results were mainly found in cockles
from England and Wales in tests conducted by CEFAS, but DARD also
found atypical results in shellfish from Northern Ireland. At
the time of writing, there have been no further atypical results
since November 2003.[15]
13. The FSA does not know what caused the atypical
results, nor what are their implications for human health.[16]
No-one has documented the presence of any known DSP toxins in
samples showing the atypical response.[17]
However, the FSA point out that
in recent years, a number of new shellfish toxins
have been described from many areas of the world. For example,
in 1995, toxins in Irish shellfish exported to other countries
caused human illness. It took four years of investigations before
the Irish authorities identified azaspiracid as the cause, and
a further two years to complete the assessment of risks to public
health. This shellfish toxin is now controlled under EU legislation.[18]
14. Furthermore, the FSA says that shellfish toxins
do not always produce an acute response and may instead give rise
to chronic effects.[19]
It recommended closure of shellfish beds which produced atypical
results as a precautionary measure. It explains its reasoning
as follows:
on the basis that something is being detected in
the MBA which is killing mice more quickly than DSP, the Agency
recommends closure of affected shellfish beds, as a precautionary
measure to protect consumer health. To do otherwise would be to
ignore the conclusions of the Phillips Inquiry into BSE on the
handling of potential threats to health arising from the food
chain. The Phillips report lays great stress on the need to take
precautionary action when the risk is uncertain.[20]
15. Although the FSA recommends closure of affected
beds, some shellfish from these beds may still reach the market.
This is because it can take four days from the time of sampling
to finding the result of the test, and in the interim shellfish
can still be sold.[21]
It is rare for a product recall to be issued in these cases, and
in any case, the fresh shellfish will already have been consumed.
The FSA says that although its primary aim is to protect public
health, it wants to act in a precautionary way. It takes the view
that consuming small amounts of shellfish over a short period
of time, as may happen in the period between sampling and getting
the test result, is not likely to cause a problem.[22]
However, to the shellfish industry, the lack of product recalls
and the absence of any known occurrences of poisoning in people
who have eaten shellfish from beds that have produced atypical
results, suggest that there is no true threat to public health.[23]
16. The FSA has commissioned a number of investigations
into the cause of the atypical results. The Laboratory of the
Government Chemist was funded to study whether Liquid Chromatography
Mass Spectrometry could be used to detect and, if possible, identify
whatever substance was responsible for producing the atypical
response. The results of this study are expected to be published
early in 2004.[24] The
FSA will also conduct a toxicology study to "inform the Agency's
consideration of the associated public health implications …[and]
policy on the closure of shellfish production areas that generate
atypical results in the MBA."[25]
10 Ev 33 Back
11
Ev 33 Back
12
Ev 32 Back
13
Ev 34, Ev 55, Ev 84 Back
14
M15 para 9 Back
15
Qq 21, 76 Back
16
Ev 35 Back
17
Ev 84 Back
18
Ev 32 Back
19
Ev 35 Back
20
Ev 35 Back
21
Ev 77, Q22 Back
22
Q51 Back
23
Q22 Back
24
Ev 34 Back
25
Ev 35 Back
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