Subject: NOR98-LIKE STRAIN OF SCRAPIE FOUND IN WYOMING
Date: April 11, 2007 at 12:47 pm PST
March 16, 2007
Wyoming Livestock Board
2020 Carey Avenue 4th Floor
Cheyenne, Wyoming 82002
For more information contact: Dr. Walter Cook at (307) 631-2974 [weekend] or (307) 777-6443 [weekday]
*****FOR IMMEDIATE RELEASE*****
NOR98-LIKE STRAIN OF SCRAPIE FOUND IN WYOMING
CHEYENNE, Wyo. - On Friday, March 16, 2007, the Wyoming Livestock Board (WLSB) was notified by officials of the USDA Animal Plant Health Inspection Service (APHIS) that an adult female sheep had tested positive for a form of scrapie consistent with the Nor98 strain. The ewe was slaughtered in Michigan, where it was tested as part of USDA’s regulatory scrapie slaughter surveillance program and traced back to a flock in Wyoming. The results of this case are distinctly different from those seen for bovine spongiform encephalopathy (BSE) or classical scrapie.
Scrapie is a transmissible spongiform encephalopathy and falls into the same category of diseases as chronic wasting disease, found in deer and elk, and bovine spongiform encephalopathy, found in cattle. The disease is limited to sheep and goats and takes years to affect an animal after it has been infected. Scrapie causes sheep to itch and scratch (scrape) wool off, change their behavior and lose body condition; it ultimately ends in death.
Nor98-like scrapie differs from classical scrapie in the distribution of brain lesions and in the course of disease progression and epidemiology. Some sheep that are genetically resistant to the classic form of the disease may be susceptible to the Nor98-like strain. Oddly, Nor98-like scrapie is usually diagnosed during surveillance in animals without clinical signs. There are no known human health risks associated with either form of scrapie.
This is the first time a Nor98-like strain of scrapie has been documented in the United States. It gets the "Nor98-like" name because it is similar to a case first diagnosed in Norway in 1998. This strain of scrapie is a rare disease even in Europe. Since 1998, fewer than 300 cases have been diagnosed in all of Europe. It is usually seen in single animals and does not tend to become widespread in a flock. In contrast, in flocks infected by classical scrapie typically more than 10 percent of the genetically susceptible animals test positive.
"This provides evidence that the surveillance program is working," said Bryce Reece, executive director of the Wyoming Wool Growers Association. "It also indicates that the program is on the cutting-edge of science to detect such a rare disease during standard surveillance."
The Wyoming Livestock Board does not expect the Nor98-like strain of scrapie to become a major disease problem for the sheep industry in Wyoming. Risk is limited because diagnosis of Nor98-like scrapie is usually an incidental event, with even highly-exposed flock mates of the positive animal normally unaffected.
The infected ewe lambed in it in what is considered a low-risk, range-lambing environment. Nonetheless, the WLSB, APHIS and the Wyoming Wool Growers Association plan to assertively pursue this case to make sure that this strain of scrapie is extinguished and does not establish itself in the U.S.
The agencies continue to encourage producers to monitor their sheep for signs of scrapie and other diseases, and to notify their veterinarian if they discover anything unusual.
The positive ewe was purchased as an adult within the last several years and moved to a Wyoming flock near the Black Hills. The producer was notified and his flock quarantined as a precautionary measure. An epidemiologic investigation is ongoing and the producer has been cooperative. The case fits the pattern found in Europe - a single, older sheep that was not exhibiting clinical signs of scrapie.
The regulatory scrapie slaughter surveillance program is a targeted slaughter surveillance program for sheep and goats designed to identify infected animals and flocks. USDA is conducting this surveillance as part of a program to eradicate scrapie from the United States by the end of 2010. Reece said that the sheep industry supports this program and is committed to eliminating scrapie from the United States.
FOIA REQUEST FOR ATYPICAL TSE INFORMATION ON VERMONT SHEEP
Re: FOIA REQUEST FOR ATYPICAL TSE INFORMATION ON VERMONT SHEEP (4843 lines)
From: Terry S. Singeltary Sr.
Date: Mon, 2 Apr 2007 14:43:32 -0500
Published online before print October 20, 2005
Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0502296102
A newly identified type of scrapie agent can naturally infect sheep with resistant PrP genotypes
( sheep prion | transgenic mice )
Annick Le Dur *, Vincent Béringue *, Olivier Andréoletti , Fabienne Reine *, Thanh Lan Laï *, Thierry Baron , Bjørn Bratberg ¶, Jean-Luc Vilotte ||, Pierre Sarradin **, Sylvie L. Benestad ¶, and Hubert Laude *
*Virologie Immunologie Moléculaires and ||Génétique Biochimique et Cytogénétique, Institut National de la Recherche Agronomique, 78350 Jouy-en-Josas, France; Unité Mixte de Recherche, Institut National de la Recherche Agronomique-Ecole Nationale Vétérinaire de Toulouse, Interactions Hôte Agent Pathogène, 31066 Toulouse, France; Agence Française de Sécurité Sanitaire des Aliments, Unité Agents Transmissibles Non Conventionnels, 69364 Lyon, France; **Pathologie Infectieuse et Immunologie, Institut National de la Recherche Agronomique, 37380 Nouzilly, France; and ¶Department of Pathology, National Veterinary Institute, 0033 Oslo, Norway
Edited by Stanley B. Prusiner, University of California, San Francisco, CA, and approved September 12, 2005 (received for review March 21, 2005)
Scrapie in small ruminants belongs to transmissible spongiform encephalopathies (TSEs), or prion diseases, a family of fatal neurodegenerative disorders that affect humans and animals and can transmit within and between species by ingestion or inoculation. Conversion of the host-encoded prion protein (PrP), normal cellular PrP (PrPc), into a misfolded form, abnormal PrP (PrPSc), plays a key role in TSE transmission and pathogenesis. The intensified surveillance of scrapie in the European Union, together with the improvement of PrPSc detection techniques, has led to the discovery of a growing number of so-called atypical scrapie cases. These include clinical Nor98 cases first identified in Norwegian sheep on the basis of unusual pathological and PrPSc molecular features and "cases" that produced discordant responses in the rapid tests currently applied to the large-scale random screening of slaughtered or fallen animals. Worryingly, a substantial proportion of such cases involved sheep with PrP genotypes known until now to confer natural resistance to conventional scrapie. Here we report that both Nor98 and discordant cases, including three sheep homozygous for the resistant PrPARR allele (A136R154R171), efficiently transmitted the disease to transgenic mice expressing ovine PrP, and that they shared unique biological and biochemical features upon propagation in mice. These observations support the view that a truly infectious TSE agent, unrecognized until recently, infects sheep and goat flocks and may have important implications in terms of scrapie control and public health.
Author contributions: H.L. designed research; A.L.D., V.B., O.A., F.R., T.L.L., J.-L.V., and H.L. performed research; T.B., B.B., P.S., and S.L.B. contributed new reagents/analytic tools; V.B., O.A., and H.L. analyzed data; and H.L. wrote the paper.
A.L.D. and V.B. contributed equally to this work.
To whom correspondence should be addressed.
Hubert Laude, E-mail: firstname.lastname@example.org
AGRICULTURAL RESEARCH COUNCIL
REPORT OF THE ADVISORY COMMITTE ON SCRAPIE
CHAIRMAN: PROFESSOR PETER WILDY
A The Present Position with respect to Scrapie
A] The Problem
Scrapie is a natural disease of sheep and goats. It is a slow
and inexorably progressive degenerative disorder of the nervous system
and it ia fatal. It is enzootic in the United Kingdom but not in all
The field problem has been reviewed by a MAFF working group
(ARC 35/77). It is difficult to assess the incidence in Britain for
a variety of reasons but the disease causes serious financial loss;
it is estimated that it cost Swaledale breeders alone $l.7 M during
the five years 1971-1975. A further inestimable loss arises from the
closure of certain export markets, in particular those of the United
States, to British sheep.
It is clear that scrapie in sheep is important commercially and
for that reason alone effective measures to control it should be
devised as quickly as possible.
Recently the question has again been brought up as to whether
scrapie is transmissible to man. This has followed reports that the
disease has been transmitted to primates. One particularly lurid
speculation (Gajdusek 1977) conjectures that the agents of scrapie,
kuru, Creutzfeldt-Jakob disease and transmissible encephalopathy of
mink are varieties of a single "virus". The U.S. Department of
Agriculture concluded that it could "no longer justify or permit
scrapie-blood line and scrapie-exposed sheep and goats to be processed
for human or animal food at slaughter or rendering plants" (ARC 84/77)"
The problem is emphasised by the finding that some strains of scrapie
produce lesions identical to the once which characterise the human
Whether true or not. the hypothesis that these agents might be
transmissible to man raises two considerations. First, the safety
of laboratory personnel requires prompt attention. Second, action
such as the "scorched meat" policy of USDA makes the solution of the
acrapie problem urgent if the sheep industry is not to suffer
Like lambs to the slaughter
31 March 2001
Magazine issue 2284
What if you can catch old-fashioned CJD by eating meat from a sheep infected
FOUR years ago, Terry Singeltary watched his mother die horribly from a
degenerative brain disease. Doctors told him it was Alzheimer's, but
Singeltary was suspicious. The diagnosis didn't fit her violent symptoms,
and he demanded an autopsy. It showed she had died of sporadic
Most doctors believe that sCJD is caused by a prion protein deforming by
chance into a killer. But Singeltary thinks otherwise. He is one of a number
of campaigners who say that some sCJD, like the variant CJD related to BSE,
is caused by eating meat from infected animals. Their suspicions have
focused on sheep carrying scrapie, a BSE-like disease that is widespread in
flocks across Europe and North America.
Now scientists in France have stumbled across new evidence that adds weight
to the campaigners' fears. To their complete surprise, the researchers found
that one strain of scrapie causes the same brain damage in ...
The complete article is 889 words long.
Adaptation of the bovine spongiform encephalopathy agent to primates and
comparison with Creutzfeldt- Jakob disease: Implications for human health
Corinne Ida Lasmézas*,, Jean-Guy Fournier*, Virginie Nouvel*, Hermann Boe*,
Domíníque Marcé*, François Lamoury*, Nicolas Kopp, Jean-Jacques Hauw§, James
Ironside¶, Moira Bruce, Dominique Dormont*, and Jean-Philippe Deslys*
* Commissariat à l'Energie Atomique, Service de Neurovirologie, Direction
des Sciences du Vivant/Département de Recherche Medicale, Centre de
Recherches du Service de Santé des Armées 60-68, Avenue du Général Leclerc,
BP 6, 92 265 Fontenay-aux-Roses Cedex, France; Hôpital Neurologique Pierre
Wertheimer, 59, Boulevard Pinel, 69003 Lyon, France; § Laboratoire de
Neuropathologie, Hôpital de la Salpêtrière, 83, Boulevard de l'Hôpital,
75013 Paris, France; ¶ Creutzfeldt-Jakob Disease Surveillance Unit, Western
General Hospital, Crewe Road, Edinburgh EH4 2XU, United Kingdom; and
Institute for Animal Health, Neuropathogenesis Unit, West Mains Road,
Edinburgh EH9 3JF, United Kingdom
Edited by D. Carleton Gajdusek, Centre National de la Recherche
Scientifique, Gif-sur-Yvette, France, and approved December 7, 2000
(received for review October 16, 2000)
There is substantial scientific evidence to support the notion that bovine
spongiform encephalopathy (BSE) has contaminated human beings, causing
variant Creutzfeldt-Jakob disease (vCJD). This disease has raised concerns
about the possibility of an iatrogenic secondary transmission to humans,
because the biological properties of the primate-adapted BSE agent are
unknown. We show that (i) BSE can be transmitted from primate to primate by
intravenous route in 25 months, and (ii) an iatrogenic transmission of vCJD
to humans could be readily recognized pathologically, whether it occurs by
the central or peripheral route. Strain typing in mice demonstrates that the
BSE agent adapts to macaques in the same way as it does to humans and
confirms that the BSE agent is responsible for vCJD not only in the United
Kingdom but also in France. The agent responsible for French iatrogenic
growth hormone-linked CJD taken as a control is very different from vCJD but
is similar to that found in one case of sporadic CJD and one sheep scrapie
isolate. These data will be key in identifying the origin of human cases of
prion disease, including accidental vCJD transmission, and could provide
bases for vCJD risk assessment.
The EMBO Journal, Vol. 19, No. 17 pp. 4425-4430, 2000
© European Molecular Biology Organization
Evidence of a molecular barrier limiting
susceptibility of humans, cattle and sheep to
chronic wasting disease
G.J. Raymond1, A. Bossers2, L.D. Raymond1, K.I. O?Rourke3,
L.E. McHolland4, P.K. Bryant III4, M.W. Miller5, E.S. Williams6, M.
and B. Caughey1,7
1NIAID/NIH Rocky Mountain Laboratories, Hamilton, MT 59840,
3USDA/ARS/ADRU, Pullman, WA 99164-7030, 4USDA/ARS/ABADRL,
Laramie, WY 82071, 5Colorado Division of Wildlife, Wildlife Research
Center, Fort Collins, CO 80526-2097, 6Department of Veterinary Sciences,
University of Wyoming, Laramie, WY 82070, USA and 2ID-Lelystad,
Institute for Animal Science and Health, Lelystad, The Netherlands
7Corresponding author e-mail: email@example.com Received June 7, 2000;
revised July 3, 2000; accepted July 5, 2000.
Chronic wasting disease (CWD) is a transmissible
spongiform encephalopathy (TSE) of deer and elk,
and little is known about its transmissibility to other
species. An important factor controlling
interspecies TSE susceptibility is prion protein (PrP)
homology between the source and recipient
species/genotypes. Furthermore, the efficiency with which
the protease-resistant PrP (PrP-res) of one
species induces the in vitro conversion of the normal PrP
(PrP-sen) of another species to the
protease-resistant state correlates with the cross-species
transmissibility of TSE agents. Here we
show that the CWD-associated PrP-res (PrPCWD) of cervids
readily induces the conversion of recombinant cervid PrP-sen
molecules to the protease-resistant state in accordance
with the known transmissibility of CWD between cervids. In contrast,
PrPCWD-induced conversions of human and bovine PrP-sen were
much less efficient, and conversion of ovine PrP-sen was
intermediate. These results demonstrate a barrier at the
molecular level that should limit the susceptibility of these non-cervid
species to CWD.
Clearly, it is premature to draw firm conclusions about CWD
passing naturally into humans, cattle and sheep, but the present
results suggest that CWD transmissions to humans would be as
limited by PrP incompatibility as transmissions of BSE or sheep
scrapie to humans. Although there is no evidence that sheep
scrapie has affected humans, it is likely that BSE has caused variant
CJD in 74 people (definite and probable variant CJD cases to
date according to the UK CJD Surveillance Unit). Given the
presumably large number of people exposed to BSE infectivity,
the susceptibility of humans may still be very low compared with
cattle, which would be consistent with the relatively inefficient
conversion of human PrP-sen by PrPBSE. Nonetheless, since
humans have apparently been infected by BSE, it would seem prudent
to take reasonable measures to limit exposure of humans
(as well as sheep and cattle) to CWD infectivity as has been
recommended for other animal TSEs.
Oral transmission of kuru, Creutzfeldt-Jakob disease, and scrapie to
Gibbs CJ Jr, Amyx HL, Bacote A, Masters CL, Gajdusek DC.
Kuru and Creutzfeldt-Jakob disease of humans and scrapie disease of
sheep and goats were transmitted to squirrel monkeys (Saimiri sciureus) that
were exposed to the infectious agents only by their nonforced consumption of
known infectious tissues. The asymptomatic incubation period in the one
monkey exposed to the virus of kuru was 36 months; that in the two monkeys
exposed to the virus of Creutzfeldt-Jakob disease was 23 and 27 months,
respectively; and that in the two monkeys exposed to the virus of scrapie
was 25 and 32 months, respectively. Careful physical examination of the
buccal cavities of all of the monkeys failed to reveal signs or oral
lesions. One additional monkey similarly exposed to kuru has remained
asymptomatic during the 39 months that it has been under observation.
Transmission of Creutzfeldt-Jakob disease by handling of dura mater.
The Lancet Volume 341(8837) January 9, 1993 pp
Weber, Thomas; Tumani, Hayrettin; Holdorff, Bernd; Collinge, John; Palmer,
Mark; Kretzschmar, Hans A.; Felgenhauer, Klaus
Sir,- Creutzfeldt-Jakob disease (CJD) can be transmitted iatrogenically by
human pituitary growth hormone, corneal transplants, and dura mater grafts
(1). Possible accidental transmission has been reported in only four
people-a neurosurgeon (2), a pathologist (3), and two laboratory technicians
(4,5) . We have encountered an unusually rapid case of CJD probably acquired
through handling of sheep and human dura mater.
In May, 1992, a 55-year-old orthopaedic surgeon developed paraesthesia of
the left arm. A few days later he had spatial disorientation, apraxia, and
gait ataxia. In June he was admitted and a neurologist suspected CJD on the
basis of the clinical signs, typical electroencephalogram (EEG) pattern, and
history. An EEG in June revealed a typical pattern of periodic biphasic and
triphasic sharp wave complexes. We saw the patient in July, 1992. He was
awake and oriented, with dyscalculia, dysgraphia, disturbed vision, apraxia
mainly of the left side, rigidity of wrists, spasticity of all muscles,
myoclonus of the left arm, increased tendon reflexes, ataxia of limbs and
trunk, and incoordination of left arm. Within 3 weeks he had impaired
consciousness and attention, mildly impaired memory, and threatening visual
hallucinations with restless turning. He had periodic states with movements
of his head and eye-bulbs resembling tonic adversive seizures. During sleep
these motor disturbances stopped. 2 1/2 months later the patient died.
This patient had worked with sheep and human dura mater from 1968 to 1972.
He handled about 150 specimens of ovine origin and at least a dozen human
preparations for research. Handling involved opening skulls with a band saw,
removing dura, and testing them either fresh (usually), preserved, or
lyophilised for mechanical qualities. These specimens were sent to a company
that has sold dura mater preparations by which CJD was transmitted in six
instances. No information was available from the company about a possible
connection with this patient's disease and the earlier cases of transmitted
CJD. Brain biopsy was consistent with diagnosis of CJD. Cerebrospinal fluid
obtained in July showed neuron-specific enolase (NSE) at 82.0 ng/mL,
compared with 16.7 ng/mL in serum of other cases (6). Proton magnetic
resonance spectroscopy of parieto-occipital and temporal grey matter,
parietal white matter, and thalamus revealed a 20-30% reduction of
N-acetylaspartate, as described (7). DNA was genotyped with allele-specific
oligonucleotides (8) and was homozygous for methionine at the polymorphic
codon 129. Subsequent direct DNA sequencing for the PrP gene open-reading
frame demonstrated normal sequence on both alleles, excluding known or novel
pathogenic PrP mutations.
It is tempting to speculate that prions were transmitted to this patient
from sheep or human dura mater through small lacerations of his skin, but
the patient and his wife did not remember any significant injury during his
four years of working with these samples. It cannot be excluded that this
was a case of sporadic CJD although this assumption is unlikely in view of
the clinical course which was similar to iatrogenic CJD transmitted by
peripheral inoculation, such as with human pituitary growth hormone or
gonadotropin or to kuru (1). Iatrogenic cases resulting from intracerebral
inoculation with the transmissible agent, for instance following dura mater
grafts (2-5), present with a dementing picture, as is usual in sporadic CJD,
rather than with ataxia as in this case.
1. Brown P, Preece MA, Will RG. "Friendly fire" in medicine: hormones,
homografts, and Creutzfeldt-Jakob disease. Lancet 1992; 340: 24-27. [Medline
Link] [Context Link]
2. Schoene WC, Masters CL, Gibbs CJ Jr, et al. Transmissible spongiform
encephalopathy (Creutzfeldt-Jakob Disease): atypical clinical and
pathological findings. Arch Neurol 1981; 38: 473-77. [Medline Link] [Context
3. Gorman DG, Benson DF, Vogel DG, Vinters HV. Creutzfeldt-Jakob disease in
a pathologist. Neurology 1992; 42: 463. [Medline Link] [Context Link]
4. Miller DC. Creutzfeldt-Jakob disease in histopathology technicians. N
Engl J Med 1988; 318: 853-54. [Medline Link] [Context Link]
5. Sitwell L, Lach B, Atack E, Atack D, Izukawa D. Creutzfeldt-Jakob disease
in histopathology technicians. N Engl J Med 1988; 318: 854. [Medline Link]
6. Wakayama Y, Shibuya S, Kawase J, Sagawa F, Hashizume Y. High
neuron-specific enolase level of cerebrospinal fluid in the early stage of
Creutzfeldt-Jakob disease. Klin Wochenschr 1987; 65: 798-801. [Medline Link]
7. Bruhn H, Weber T, Thorwirth V, Frahm J. In-vivo monitoring of neuronal
loss in Creutzfeldt-Jakob disease by proton magnetic resonance spectroscopy.
Lancet 1991; 337: 1610-11. [Medline Link] [Context Link]
8. Collinge J, Palmer MS, Dryden AJ. Genetic predisposition to iatrogenic
Creutzfeldt-Jakob disease. Lancet 1991; 337: 1444-42. [Medlin
USA MAD COW STRAIN MORE VIRULENT TO HUMANS THAN UK STRAIN
18 January 2007 - Draft minutes of the SEAC 95 meeting (426 KB) held on 7
December 2006 are now available.
64. A member noted that at the recent Neuroprion meeting, a study was
presented showing that in transgenic mice BSE passaged in sheep may be more
virulent and infectious to a wider range of species than bovine derived BSE.
Other work presented suggested that BSE and bovine amyloidotic spongiform
encephalopathy (BASE) MAY BE RELATED. A mutation had been identified in the
prion protein gene in an AMERICAN BASE CASE THAT WAS SIMILAR IN NATURE TO A
MUTATION FOUND IN CASES OF SPORADIC CJD.
3:30 Transmission of the Italian Atypical BSE (BASE) in Humanized Mouse
Models Qingzhong Kong, Ph.D., Assistant Professor, Pathology, Case Western Reserve
Bovine Amyloid Spongiform Encephalopathy (BASE) is an atypical BSE strain
discovered recently in Italy, and similar or different atypical BSE cases
were also reported in other countries. The infectivity and phenotypes of
these atypical BSE strains in humans are unknown. In collaboration with
Pierluigi Gambetti, as well as Maria Caramelli and her co-workers, we have
inoculated transgenic mice expressing human prion protein with brain
homogenates from BASE or BSE infected cattle. Our data shows that about half
of the BASE-inoculated mice became infected with an average incubation time
of about 19 months; in contrast, none of the BSE-inoculated mice appear to
be infected after more than 2 years.
***These results indicate that BASE is transmissible to humans and suggest that BASE is more virulent than
classical BSE in humans.***
6:30 Close of Day One
SEE STEADY INCREASE IN SPORADIC CJD IN THE USA FROM
1997 TO 2006. SPORADIC CJD CASES TRIPLED, with phenotype
of 'UNKNOWN' strain growing. ...
There is a growing number of human CJD cases, and they were presented last
week in San Francisco by Luigi Gambatti(?) from his CJD surveillance
He estimates that it may be up to 14 or 15 persons which display selectively
SPRPSC and practically no detected RPRPSC proteins.
Diagnosis and Reporting of Creutzfeldt-Jakob Disease
Singeltary, Sr et al. JAMA.2001; 285: 733-734.
BRITISH MEDICAL JOURNAL
JOURNAL OF NEUROLOGY
MARCH 26, 2003
RE-Monitoring the occurrence of emerging forms of Creutzfeldt-Jakob
disease in the United States
Email Terry S. Singeltary:
I lost my mother to hvCJD (Heidenhain Variant CJD). I would like to
comment on the CDC's attempts to monitor the occurrence of emerging
forms of CJD. Asante, Collinge et al  have reported that BSE
transmission to the 129-methionine genotype can lead to an alternate
phenotype that is indistinguishable from type 2 PrPSc, the commonest
sporadic CJD. However, CJD and all human TSEs are not reportable
nationally. CJD and all human TSEs must be made reportable in every
state and internationally. I hope that the CDC does not continue to
expect us to still believe that the 85%+ of all CJD cases which are
sporadic are all spontaneous, without route/source. We have many TSEs in
the USA in both animal and man. CWD in deer/elk is spreading rapidly and
CWD does transmit to mink, ferret, cattle, and squirrel monkey by
intracerebral inoculation. With the known incubation periods in other
TSEs, oral transmission studies of CWD may take much longer. Every
victim/family of CJD/TSEs should be asked about route and source of this
agent. To prolong this will only spread the agent and needlessly expose
others. In light of the findings of Asante and Collinge et al, there
should be drastic measures to safeguard the medical and surgical arena
from sporadic CJDs and all human TSEs. I only ponder how many sporadic
CJDs in the USA are type 2 PrPSc?