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From: TSS ()
Date: March 27, 2005 at 9:31 am PST

-------- Original Message --------
Date: Sun, 27 Mar 2005 11:20:35 -0600
From: "Terry S. Singeltary Sr."
Reply-To: Bovine Spongiform Encephalopathy

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



Foodborne Contaminants Research

Project Number: 5325-32000-003-02
Project Type: Specific C/A

Start Date: Aug 01, 2004
End Date: Jul 31, 2005

The goal of the proposed research is to develop molecular methods to
distinguish and thereby analyze different prion strains. If successful,
these methods could be used to address the following question: Is the
December, 2003 North American BSE case the same strain as the United
Kingdom BSE strain, or is it analogous to rare atypical BSE cases such
as those seen in Italy and Japan? The UK strain has been linked to feed
contaminated with BSE, wheras the atypical cases are hypothesized to be
of sporadic origin. The answer to this question has obvious implications
for 1) the scientific basis of regulations that are designed to prevent
future BSE cases caused by feed contamination and 2) the explanation as
to the cause of future BSE cases which may still arise despite 100%
compliance of feed ban regulations.

Transmissible spongiform encephalophies (TSEs) affect humans and
domesticated animals such as sheep (scrapie) and cattle (BSE). TSEs can
be genetic (inherited mutations in the prion gene), infectious (dietary
or accidental exposure to prions as in iatrogenic cases or consumption
of prion-infected food) or sporadic v.g. sporadic Cruetzfeld-Jacob
Disease (CJD). Prions have properties that are maintained upon
transmission from one host to the next, allowing different 'strains' to
be distinguished. Strains cause specific phenotypes, such as different
symptoms, incubation time, and tissue distribution of PrPSc.
Differentiation of strains is of paramount importance: as an example,
the strain of sheep PrPSc that causes scrapie is not transmissible to
humans, while the strain that causes ovine BSE presumably is. By
SDS-PAGE analysis, PrPSc from different strains maintain specific ratios
of non-, mono-, and di-glycosylated glycoforms and different size of the
proteinase K (PK) resistent core. However, these methods have
significant limitations. Some strains exhibit similar glycoform
patterns, and prions of a given strain isolated from different regions
of the brain show differences in glycoform patterns, leading to
uncertainty. Examination of the molecular weight of PrPSc after
proteolysis by SDS-PAGE can only distinguish gross molecular weight
differences. We propose to develop new methods to differentiate prion
strains based on mass spectrometric analysis. Specifically, we will use
tandem mass spectrometry to identify and quantitate peptides of
different molecular weights after treatment of the PK-resistant core
with trypsin. We will inoculate Syrian hamsters with different prion
strains in BL-2 facilities. PrPSc will be isolated from their brains,
digested with PK, and denatured. Inactivated prions can then be safely
shipped, cleaved with trypsin and analyzed by nanoLC-ESI-MSMS at the
WRRC. The scope of this work is to provide proof of principle in a well
characterized animal model. If sucessful, future effort will focus on
adaptation from animal models to BSE. Documents SCA with U. of
Compostela Santiago.

> The UK strain has been linked to feed contaminated with BSE, wheras
> the atypical cases are hypothesized to be of sporadic origin.


on what scientific basis do these atypical BSE/TSE in cattle,
on what scientific basis is there that feed was not a factor ???

or vertical and or lateral transmission ???

Horizontal and vertical transmission

[Horizontal Transmission
[Vertical Transmission
[Maternal Transmission

Horizontal and vertical transmission refers to the transfer of infection
from animal to animal, except that vertical transmission refers
specifically to spread from parent to calf. A specific form of vertical
transmission is maternal transmission, which refers to spread from cow
to calf, either whilst in the womb or afterbirth.

Defra has funded specific studies to attempt to determine whether or not
BSE does spread by these routes. However, the fact that the within herd
incidence of BSE rose no higher than 2.7% is a good indicator that
infection does not spread from cow to cow to any significant extent.

Horizontal transmission

If any transmission does take place at all, the evidence from sheep
scrapie suggests that the calving cow probably represents the greatest
risk to other cattle. A recent study has shown that lambs born to ewes
introduced into a scrapie flock became infected and died at the same age
as lambs born to native ewes, consistent with lateral transmission of
scrapie to lambs (Research in Veterinary Science 76 (2004) 211217).
While there has been a study showing some evidence for horizontal
transmissions up to three days after calving, there was no evidence of
transmission to the cow's own calf, (Hoinville et al. 1995. Veterinary
Record. 136, 312-318). However, the results were considered
statistically insufficient to suggest that horizontal transmission was

Another method of testing this theory involved the feeding of calves
with placenta from confirmed cases of BSE. The calves that were
challenged were clinically normal prior to slaughter and their tissues
are being assayed for infectivity to find out if the cattle became
infected without succumbing to clinical disease. Some preliminary tissue
assays have been completed, without any infectivity being detected.

Professor Andersons group's work, has given rise to speculation about
the possibility that horizontal transmission may arise on farms. The
conclusion state quite clearly that:-

"it should be emphasised that to date no evidence exists supporting the
hypothesis of direct horizontal transmission." and,

"produces no evidence to support the hypothesis that horizontal
transmission is occurring at a rate sufficient to allow BSE to become

Their, and previous studies have however indicated that bigger herds are
at greater risk of acquiring BSE than smaller herds.

This correlation of risk with herd size has in fact been known and
published for several years. (Wilesmith et al, in Veterinary Record,
130. 90-94. Wilesmith, 1996, Bovine Spongiform Encephalopathy. The BSE
Dilemma (p45-55).

The finding is consistent with the original suggested explanation that
the larger the herd the greater the probability of purchasing an
infected batch of feed.

Vertical transmission - from the sire

Epidemiological studies have compared the incidence of BSE in the
offspring of healthy bulls and those of bulls that later were confirmed
to have BSE. There was no difference between the groups that could be
attributed to the BSE status of the bull. Further data obtained from
Artificial Insemination (AI) organisations have been analysed in order
to expand and update previous studies, but no risk from semen used for
commercial AI has been identified.

Experimental transmissions have also been attempted using semen, seminal
vesicles and prostate of bulls confirmed to have BSE, but no infectivity
was detected in these samples. (Wilesmith, J. W. 1994. New Zealand
Veterinary Journal. 42. 1-8).

Maternal transmission

In formulating BSE policy the UK has always assumed that maternal
transmission could occur, but calculated that it would do so
infrequently and so would not prevent the eradication of BSE. Apart from
the general epidemiological analyses, and modelling of expected versus
observed frequencies of disease in cattle that had BSE affected mothers,
a specific study was established to study whether maternal transmission
occurred, and if so at what rate.

A summary of the findings were discussed at the Spongiform
Encephalopathy Advisory Committee (SEAC) on 17 April 1997, and showed
that calves which are the offspring of clinical cases have an enhanced
risk of developing BSE. The overall risk difference was 9.6% as compared
to non-BSE cases. In a separate study of the entire database, the risk
was highest in calves born after clinical onset in the dam, and for
calves born before clinical onset the risks decreased rapidly, with no
maternal effect being detectable in calves born more than two years
before the onset of clinical disease in the dam. It remains uncertain
whether this effect represents true maternal transmission of infection
from cow to calf or genetic susceptibility to a feed source of
infection, or a mixture of both.

Having considered the evidence, SEAC recommended that the Government
should consider the options for a cull of offspring. The Committee
confirmed however that it was satisfied that existing controls to
protect the consumer were adequate. The scheme will have some benefits
in terms of the eradication of BSE, although these are thought to be
relatively small. It will prevent some cases of BSE occurring in
offspring kept for breeding or milking and prevent any of those animals
from infecting their calves.

As a result of the retrospective offspring cull
is taking place now and the on-going prospective cull that will follow
it the number of animals on-farm with maternally derived infections will
be reduced. These will be animals where the mother was known to have
been infected and its calves were traced and culled before they were
slaughtered for human consumption.

Continued risks from contaminated feed

The ongoing epidemiological monitoring attempted to establish the
reasons for the continuation of the epidemic in animals born after the
ruminant feed ban of July 1988. In the absence of maternal and/or
horizontal transmission there had to be another reason for the

Although the ban clearly worked very well, it seems not to have been
absolute. In particular there has been a shift of the epidemic after the
ban both northwards and eastwards. There was a direct correlation
between the incidence of BSE in cattle born in 1990 or later with the
size of the local pig and/or poultry population. There was no direct
correlation between the presence or absence of these species on farm and
the incidence of BSE in cattle on the same farm. The pig and poultry
populations are at their densest in the northern and eastern parts of
England. Feed manufactured for such farms was usually, but not always,
produced in mills that also compounded feed for cattle and other
species. It was perfectly legal, until the end of March 1996, to include
ruminant protein, in the form of meat and bone meal, in pig and poultry
rations. Until September 1990 that meal would also have included meal
derived from rendering specified bovine offals. Further investigations
led to the conclusion that, feed manufacturers that produced products
for cattle as well as pigs and/or poultry ran a risk of accidentally
incorporating ruminant protein in their cattle rations.

Additional investigations involving experimental challenge of calves by
mouth with brain from confirmed cases of BSE indicated that as little as
1g of brain could infect calves. This highlighted the importance of
tight quality control in the feed mill in preventing cross contamination
on a scale that could still infect cattle. Indeed in 1996, after testing
of feed produced in mills indicated that it was extremely difficult to
prevent cross-contamination, a decision was taken to ban the use of meat
and bone meal altogether in order to eliminate that risk.

where is evidence of spontaneous (sporadic) TSE in these atypical
cattle ???


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