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From: TSS (
Date: January 25, 2005 at 9:05 am PST

-------- Original Message --------
Date: Tue, 25 Jan 2005 10:23:01 -0600
From: "Terry S. Singeltary Sr."
Reply-To: Bovine Spongiform Encephalopathy

##################### Bovine Spongiform Encephalopathy #####################

Sporadic CJD clusters ‘not random’

A study of 220 sporadic CJD cases occurring in the UK from 1990 to 1998
has suggested that
the clustering of the cases is unlikely to be due to purely random
effects.1 Compared with
age-, sex- and hospital-matched controls, the residential proximity of
cases during various
time periods was compared with that expected in the absence of any
clustering. Sporadic
CJD cases lived closer together than might be expected in the absence of
any diseaseclustering
mechanism. This evidence became stronger as the critical period during which
residential proximity was required to have occurred extended further
into the past.
The authors suggest that some sporadic CJD cases were likely to have
been caused by
exposure to a common external factor. The overall rarity of sporadic CJD
indicates that
repeated point-source outbreaks of the disease are more likely to
explain the clustering
than direct case-to-case transmission. Identifying sources of such
outbreaks many years
after the event will be extremely difficult, they say.
Infectivity in blood despite negative tests
Blood may be infective for TSEs while failing to show the characteristic
presence of
proteinase-resistant forms of prion, according to a study by US
scientists.2 Infectivity may
be caused by prions which are partially protease-sensitive, but this
means that pretreatment
with protease – which is routine for Western blot assay—is likely to
give false
negative results.
The probable transmission of CJD through blood transfusion from a
pre-symptomatic case in
the UK has underlined the need for a reliable, sensitive, and specific
screening test, but
attempts to identify abnormal prions, which are usually resistant to
protease, by treating
the blood with protease and searching for the remaining resistant prions
have so far failed.
In the present study, samples of blood plasma were taken from infected
mice at the time
they first showed symptoms, and the plasma samples were treated with
either 100 and 500
microg per mL of protease or left untreated. Infectivity was bioassayed
by intra-cerebral
inoculation into healthy mice: the results showed that treatment of
plasma with 100 or 500
microg per mL protease gave infectivity levels of 8.4 and 5.2 IU per mL
compared with
infectivity from untreated control plasma of 20.6 IU per mL. No
protease-resistant prions
were detected in plasma samples by Western blotting.
The authors conclude that infectivity may be reduced but not eliminated
by treatment with
protease, indicating that some of the infectivity may be due to the
presence of infective
prions that are partly proteinase-sensitive. Pre-treatment with protease
will make their
detection more difficult.
BSE: youngest cattle are most at risk
Cattle under the age of six months are at greatest risk of developing
BSE following exposure
to tainted feed, according to statisticians at the UK Veterinary
Laboratory Agency.3 The
researchers used back-calculation methods to analyse BSE-epidemic data
collected in Great
Britain between 1984 and 1996. An initial review of unpublished data on
the use of
proprietary concentrated feeds for dairy-replacement cattle showed that
autumn- and
spring-born cattle would receive different feeding patterns of
concentrates, and so agedependent
risk of infection profiles were obtained separately for autumn- and
cattle. The results showed that dairy cattle were most at risk in the
first 6 months of life
while cattle aged over 24 months were at relatively low risk of
infection. Between 6 and 24
months of age, risk profiles reflected feeding patterns of proprietary
concentrates in each
of the autumn- and spring-born cohorts.
600oC incineration not enough to destroy TSE
An investigation into the effectiveness of 15 min exposures to 600oC and
1000oC in
continuous flow incineration-like conditions found some infectivity
present in a sample
burnt in normal air at 600oC.4 The tests used samples of pooled brain
macerates from
hamsters infected with the 263K strain of hamster-adapted scrapie with
an infectivity titer
in excess of 10(9) mean lethal doses (LD50) per g. Bioassays of the ash,
outflow tubing
residues, and vented emissions from heating 1 g of tissue samples
yielded a total of two
transmissions among 21 inoculated animals from the ash of a single
specimen burned in
normal air at 600oC. No other ash, residue, or emission from samples
heated at either 600
1000o C, under either normal or starved-air conditions, transmitted
disease. The findings
are similar to those found in earlier experiments which also found
continuing infectivity at
600oC in laboratory chambers. The current tests mimic incinerators.
The authors conclude that at temperatures approaching 1000oC under the
air conditions and
combustion times used in these experiments, contaminated tissues can be
inactivated, with no release of infectivity into the environment from
emissions. The extent
to which this result can be realized in actual incinerators and other
combustion devices will
depend, they say, on equipment design and operating conditions during
the heating


Pseudohypersomnia reported in FFD

French researchers have presented a case of fatal familial insomnia,
confirmed genetically,
in which profound changes in the normal sleep-wake cycle showed
unusually excessive
sleeping – pseudohypersomnia behavior – instead of insomnia.18 There was
also a clear
dissociation in the disappearance of circadian and neuroendocrine
rhythms, findings
unrelated to abnormalities in thyroid activity.


US food inspectors express SRM concerns

US meat plants are allowing brains and spinal cord from older cattle to
enter the food
supply, violating strict government regulations aimed at preventing the
spread of BSE, a
federal meat inspectors union has claimed.24 Nearly a year after the
first US case of BSE,
meat plants have yet to implement measures required by the US
Agriculture Department to
protect consumers, according to the National Joint Council of Food
Inspection Locals.
‘We know USDA's zero tolerance is not being met,’ said union chairman
Stan Painter. ‘We
believe this is a widespread problem." He declined to say how many
plants were in
violation. In October, US meat inspectors began alerting the union that
plant employees
were incorrectly identifying carcases of animals over 30 months old,
Painter said. Under
USDA procedures, plant employees are responsible for identifying older
cattle by examining
their teeth. Painter said these violations allowed prohibited parts to
slip by inspectors and
enter the food supply.
Painter said slaughter plants needed to segregate their production lines
by age. The union
also urged the USDA to give inspectors more authority to enforce
regulations. The union
told the USDA about its concerns in a letter on 8 December. The USDA
said it had received
the letter and would soon respond.


Questions on USDA’s BSE test protocols

Following the report from the USDA that a cow showing two inconclusive
rapid tests had
been declared BSE negative on a final test has raised concerns in
internet discussion groups
that the test procedures being used by the USDA for BSE in cattle
creates problems with
defining and detecting positive cases. For the rapid BioRad tests
approved by the USDA,
interpretation of test results gives some latitude for calling a result
‘Inconclusive’ and
leaves unspecified categories below ‘Negative’ and between ‘Negative’ and
BioRad results:
0.00 – < 0.03 ?
0.03 – 0.15 = NEGATIVE
> 0.15 – 0.18 ?
> 0.18 – < 0.80 = INCONCLUSIVE
0.80 and above = POSITIVE
Inconclusive results would necessitate more testing, while negative
results would receive no
further testing. Brad Crutchfield, vice president of Bio-Rad, reportedly
told Reuters: "After
two inconclusive results, you have a much higher rate of confirming
(BSE)" in the final test.
He said the accuracy of Bio-Rad's test was over 95 percent. The USDA
finding of a negative
follow-up test using immunohistochemical (IHC) methods after two
inconclusive BioRad
tests raised concerns that IHC testing may be flawed: Critics have
suggested that the
follow-up IHC testing will be done on different pieces of tissue, and
will be done on tissue
that may be older and poorly identified. A negative result using IHC
does not necessarily
mean the animal was BSE-free.


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