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Atypical BSE-Japans 23 month old case

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Mike

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KEY WORDS: Bovine spongiform encephalopathy, BSE, Western blot, atypical
BSE.

ABSTRACT

For many years, researchers believed that only one bovine spongiform
encephalopathy (BSE) strain existed, in contrast to the many different
scrapie strains found. However, only very recently reports emerged about
unconventional BSE strains seen in Italy, France, and Japan. The present
case describes an atypical strain of BSE in Belgium in a 64-month-old
East-Flemish cow with an electrophoretic profile and other features
similar to those described in Japan.

INTRODUCTION

Transmissible spongiform encephalopathies (TSEs), or prion diseases, are
a group of fatal neurodegenerative diseases including sheep and goat
scrapie, bovine spongiform encephalopathy (BSE), and Creutzfeldt-Jakob
disease (CJD) in humans. They are characterized by the accumulation of
an abnormal protein, called PrPsc, which is formed post-translationally
from the normal isoform (PrPc).1,2 At present, the agent causing TSEs is
still incompletely characterized, although PrPsc is believed to be its
major if not unique constituent.3

Research in mice showed the existence of different scrapie strains.4,5
Scrapie strain discrimination is currently based on biologic typing in a
panel of inbred mice, using incubation time and brain pathology scoring
as criteria.6 However, no large-scale studies of the molecular features
of PrPsc have been reported for bovine BSE to date. Till now, the BSE
strain seemed to maintain constant biologic and molecular properties
even after experimental or accidental passages into different species,
such as mice, humans, primates, and sheep.710 However, very recently,
variant forms of BSE have been reported in Japan, Italy, and
France.11-13 These forms were characterized by atypical histopathologic,
immunohistochemical, or biochemical phenotypes. The present case is the
description of the first atypical BSE case in Belgium.

MATERIALS AND METHODS

Since January 2001, all cattle older than 30 months are tested for TSE
via a rapid test (TeSeE-kit, Bio-Rad, Nazareth, Belgium) after EC
regulation 999/2001.14,15 Samples positive according to the
enzyme-linked immunosorbent assay (ELISA) screening are further
subjected to scrapie-associated fibrils (SAF), histopathology,
immunohistochemistry, and Western blot (WB) testing16,17 at the National
Reference Laboratory (NRL).

RESULTS

A positive ELISA sample from a 64-month-old East-Flemish cow or Belgian
white and red (Figure 1) was presented at the NRL for confirmation. The
animal was reported healthy before slaughter. The optical density (OD)
titers at the local laboratory were 2.324 and 2.116.16 The OD titers at
the NRL were 0.953 and 0.708 (sample taken at the contralateral side of
the first sampling side of the obex region). The histopathology of the
obex, pons, and midbrain showed no spongiform changes;
immunohistochemistry of the brainstem revealed no signal of PrPsc
accumulation typical for BSE; and SAF was negative. However, WB analysis
(Bovine WB, Bio-Rad, France; antibodies 12F10 and SAF60) of the same
homogenate that was prepared from the obex region for ELISA revealed a
small amount of PrPsc with an electrophoretic profile different from
that of typical BSE-associated PrPsc.18,19 The band on the gel of the
non-glycosylated form of PrPsc of the present case clearly showed a
lower migration pattern compared with that of a typical BSE case (Figure 2).

DISCUSSION

For many years, researchers assumed that only one BSE strain
existed.710 Only in the past months, reports of atypical BSE cases were
announced.1113 The Japanese case11 describes a very young bull (23
months) characterized by the absence of spongiform changes and PrPsc
deposits immunohistochemically. The WB analysis revealed an
electrophoretic profile different from that of typical BSE,
characterized by low content of the di-glycosylated molecular form of
PrPsc and a faster migration of the nonglycosylated form of PrPsc. In
Italy,12 two BSE affected cattle with a previously unrecognized
neuropathologic profile and PrPsc type were seen. These cases were
determined using a different staining pattern on immunohistochemistry, a
difference in size and glycoform ratio of PrPsc on immunoblot and a
difference in regional distribution of lesions. The two cases in
France13 showed variant molecular features with a different PrPsc
electrophoretic profile from other BSE cases, mainly characterized by a
higher molecular mass of the nonglycosylated PrPsc. The present case
shows the most similarities (ie, identical electrophoretic profile, only
ELISA and WB positive and histopathology and immunohistochemistry
negative) with the Japanese case,11 although the cow in the Japanese
case was only 23 months old, and the cow in this case was 64 months old.

The fact that these strains were detected worldwide and in several
breeds suggest that there is no local or breed-dependent feature
involved. It could be that the WB techniques have become more specific
within the past year in the detection of minor differences in di-,
mono-, and nonglycosylated molecular forms of PrPsc. Infection of cattle
by scrapie could also be considered since scrapie can be transmitted by
direct contact between animals or through environmental contamination.13

In conclusion, this Belgian case should be added to the list of atypical
BSE strains only very recently detected worldwide and may contribute to
further research studies about epidemiologic significance. Current
continued research on BSE would appear to reveal different BSE strains
in analogy with the different scrapie strains.
 

Mike

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The samples sent to Weybridge at this time will come back negative for BSE (because of the Atypical strain) and no furthur tests will be possible because of the shortage of sample materials. What then?
 

Mike

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reader (the Second) said:
If this is the way it's scripted, I'm afraid it won't get an Oscar with the international audience although the domestic audience appears to love the happy endings that USDA puts out.

If it is negative, I'd sure like to hear the explanation for why the "weak positive."

Yea, Charlie Chaplin type comedies aren't popular anymore. :wink:
 

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