Jpn. J. Infect. Dis., 53, 56‑61, 2000

Review
Japanese Scr叩ie Cases

Takashi Onodera* and Keiichi Saeki
Department of Molecular Immunology, School ofAgricultural and
Llfe Sciences, UniversiO/ of Too/0,
BunbJo‑ku, TobJo 113‑8657, Japan(Received April 24, 2000. Accepted May 22, 2000)

SUMMARY: Worldwide attention has been given to scr.apie, because bovine spongiformencephalopathy (BSE)
could be experimentally transmi仕ed to sheep. This ovlne fbm of BSE was clinically identical to scrapie. In

Japanese scrapie cases, a majorityofthe diseqsed sheep were from Suffolk, while 8 cases were from Corriedale･
It is very likely仇at sheep‑to‑sheep transmisslOn Ofscr叩ie has taken place in Obihiro, Hokkaido. Nomal prlOnprotein may play a role in the morphorFgulatory signaling pathwa.y, which orchestrates the specirlCityof aparticular cellular response. Over‑express10n Of normal pr10n Protein ln mice cause neurodegenerative disorders.

Recently, Prndwas identified downstream of the mouse prion protein gene (Prnp), and encodes 1 79 amino acids
and a prion protein (PrP)‑like protein designated doppel (Dpl)･ Dpl was upregulatedinthe centralne㌣ous system

oftwo PrP‑deficient lines of mice, as well as in prlOnless cell lines. Dpl caused neurodegeneration slmilar to thatcaused by PrP. Linked expression ofPrnp and Prnd may cause several neurodegenerative disorders.

transmissible among sheep by both natural means and1. Introduction

experimentally by injection of healthy animals with scraple

Prions cause degenerative disease of the central nervous

brain homogenates (13, 14)･ The natural infection route issystem (CNS)inboth humane and animals ( I ‑4)･ Prion proteinsthought to occur by matemal transmlSSion (and possibly, inare composed or the scraple isofbrm of the prlOn proteinrare case, by sire transmission), scarification on fences, Or(PrPSc), and the nomal cellular isofbm or the prion protein

exposure to placental tissues in the field. Experiments with

(PrPC)( 1 )･ Investigations ofprion diseases have taken onヮew

sheep revealed that inoculation through various routes affected

importance in the wake of reports of an atyplCal, varlant

the incubation period of the disease; the incubation period

Creutzfeldt‑Jakob diseases (5‑8). All of the cases have beenreported from Great Britain, Ireland, and France to date. It
seems likely that bovine pr10nS from bovine spongiform

was longer irthe animals had been inoculated subcutaneously
than if they had been inoculated intracerebrally ( 1 5). Inocula‑tion ofCheviot sheep with a short incubation strain of scraple

encephalopathy (BSE) Were transmitted to humans throughindicated that the incidence of scraple in the offsprlng Was

the consumptlOn Or tainted beef products. Worldwide atten‑

directly influenced by the incidence of scraple Observed intion has been focused on scrapie because of experimental
results revealing the oral transmission of BSE to sheep. If

the parents. If both parents were negative for scraple, thePostmortem neuropathologICal findings usually show grossspongifbm degeneration in the brain (2) due to vacuolation

offspring would be negative. However, if one parent was posi‑
tive, the progeny had a greater than 40% chance of contracting
scraple, and if both parents were positive for scrapie, 70% of
the lambs were likely die fTrom scrapie (1 6). Matings between
Cheviot and Suffolk sheep and subsequent experiments upon
the offspring led to the conclusion that the scraple incubation

contaminated meat and bone meal has been fed to sheep, thenit is possible that an ovine formofBSE (9), clinically identicalto scraple, exists.

in the dendritic and axonal processes and in the cell bodies of

period was prlnClpally controlled by a slngle autosomal geneneurons. Proliferation of the astroghal cells isalso common,

termed Sip (旦crapie王ncubation旦eriod)with two alleles

along with the presence of amyloid plaques which contain

designated sA and pA (16).

fibrils of a disease‑specific form of the host cell surface. On
normal cells, this protein (PrP) is proteinase K sensitive

inoculation with a particular strain of scraple are actually(PrPC)(10), but becomes resistant to digestion (PrPSc) duringresistant or whether the incubation period is so long until pnor

There is the question whether sheep that survive after

the disease process (I 1). The agent appears to be intimately

to the appearance of clinical signs, and sometimes animals die

involved with this proteinase K‑resistant protein (PrPSc). In

without any symptoms. This extended incubation period may

this report,仇e epidemiology or Japanese scr叩le is described.

be important, glVlng that sheep are capab)e ofpasslng SCraPle

In the latter part, mechanisms for the pathogenesis and roleon through matemal transmission. In the case ofDickinson'sor prpC are reviewed.

experiment (1968), the whole れock was inoculated, and"resistant" sheep have been used to produce a scraple‑resistantmock. lt was Dickinson himself who questioned the idea of

2. Scraple agent in sheep

resistance and whether the animals were in fact infected with

Sheep scraple Was Originally thought to be a genetic disorder,

scrapie, but their lifespan of the animals coupled.With thedue to the long incubation period and vertical transfer ( I 2).

incubation period or the scraple meant that the disease did

Early experiments confirmed that the disease was horizontally

not reach the clinical stage (17). Unfortunately, attempts tocreate scraple‑resistant mocks are also hampered by the*Corresponding author: Tel/Fax: +81‑3‑584ト8020, E‑mail:accelerated action or other scraple Strains in some breeds.

aonoder@mail. ecc.u‑tokyo. ac.jp

This question or resistance may also be important when56

addresslng the species barrier, which will be described later.

there (22).

From 1989 to 1990, four Comiedale sheep (lessthan 2 years
old) died for no obviou! reason･ Based on histopathological

3. Epidemiology of scraple

examination, a diagnosIS Of scraple Was made in Hokkaido

Scrapie affects most breeds of sheep. It has a widespread
distributioninthe world but has been successfully eradicatedin Australia, where it was established only locallyand briefly,
following importation (1 8)from New Zealand, and from some(23) as well as in Fukushimaand Miyazaki (Fig. 1). In addi‑tion, a few cases of scraple With pruritus have been reported

in Suffok and Corriedale sheepinJapanover the past 10 years(21‑25) (Table 1). All of these sheep had been transferredfrom a farmin Hokkaido with a history of incidence of scraple
in Suffolk sheep except ln One Case in Yamagata in 1983, andlocations and flocks in Iceland. Some countries in SouthAmerica and Europe are also hkely free of the disease.

in one case in Fukushima in 1984.

In Japan, since the丘rst ou他reak of scr叩1e in Obihiro of

Hokkaidoin1 984 ( 1 9, 20), poshortem braintissues have been

It was recognized that all of these cases with the ataxia

attained in more than 20 cases of pathologically confirmed

type of scraple Were enZOOtic, and all of the sheep with thescrapie. Since attention was drawn to the syndrome ofovine

ataxia type of scrapie belonged to the Comiedale breed (Table

scraple, Particularly its lateral transmission in Obihiro area,1). In 1989 0bihiro case, a 19‑month‑old Corriedale ewemore frequent diagnoses have been undertaken than before

suffering from cryptogenic dysstasia for 2 months wasby various animal health stations in Hokkaido (2 I). Duringsacrificed and examined by histological method. The sheep

the period from 1984 to 1986, approximately 50 cases were

was smaller thanhealthy sheep of the same age. No sigmificant

reported in Hokkaido, and more than 10 cases outside
Hokkaido; i.e., One scrapie‑like diseaseincidence in Yamagata
in 1 983 , two pathologically confirmed cases in Yamagata andneⅣe cells and spongifbm lesions were obseⅣed mainly inFukushima, respectively, in 1 984,and additional scrapie‑likethe brain stem (25). Scrapie‑associated fibril (SAF) proteinsdisease cases in Iwate, Ibaraki, and Chiba in 1984. In 1987,

were also detectedinthe brainextract of this case by Westemblot analysis (WBA). In 199 I Fukushima case, the sheep wasgross pathological lesions were fわund in any or the organs

including CNS. Histopathologically, the majorityof vacuolated

threeincidences were reportedinKanagawa, and the presenceof scraple Was Pathologically confirmed in one case by brain
tissueinspection (Fig. 1‑3). In regard to the duration ofovinefrom a farm with a history of incidence of scraple Prior to its

transference to an animal facility. She was two years oldand

scrapie disease, it is a 3‑ to 6‑month period on average in

did not show any clinical symptoms, even when she was kept

Suffolk sheep. It is quite probable that sheep‑to‑sheep trans‑mission of scraple took place in Obihiro, Hokkaido, sincein the same facility with another scraple‑affected sheep thatapproximately 50 casesinSuffolk andthree casesinComiedaleorlginated from sheep in Obihiro or those transferred from

Fig. 2. Pruritus observed inthe shoulder ofa scrapie‑affccted sheep ln
Kanagawa.

Fig. I. Distribution ofscrapie‑affected sheep by prefecture, 1984 to
1999.

Fig. 3. Single and multiple vacuolesinnerve cells of the nucleus olivaris@ : Affected sheep pathologically confirmed

in a scr叩ie case in Hokkaido. H‑E staining (× 600).

◎ : Affected sheep conRrmed bypersonalcommunication

57

Table 1. Clinical sign orscraple in Japan
Pruritus typeAge or sheep

3‑4 years old

Number or sheep*

28

Ataxia type
ト2

years

old

4

Asymptomatic type
2

years

old

1

Reported in

1984‑1987

198811999

Breed of sheep

Suffolk, ComiedaleCo汀iedale

Symp tons

Pmritus, Ataxia

AtaxiaParalysュ S

ParalysIS

Duration of disease

2‑3 months

0.5‑1 month

Histopathology

Spongiform

Spongifbm Spongifbm

Enc ep ha lopathy

Enc ep halop athy Enc eph a lopathy

1991

Co汀iedale* Number of sheep observed in the National Institute ofAmimal Health, Ibaraki･

on sacrifice. Vacuolated nerve cells were found throughout

Confbmational and posttranslational changes･ However, lt
is hard to imaglne 20 0r more stable pathogenic confb‑a‑the brain stem. SAF protein was detected in the brain andtional changes in one protein which has the same amino acidwas devoid ofpruritus. The sheep was three months pregnant

spleep extract by WBA (24)･ 1n most of the recent Japanesesequences. Since some strains can be passaged unchanged

scr叩】e Cases, SCratChing has not been a symptom･ Therefわre,between two species, each has its own PrP primary stmcture･

veterinarians who examine sheep clinically and pathologlCally
should consider this asymptomatic condition recently reported

Bessen and Marsh (36) suggested that there were differencesin conformation on the basis of different rates of digestion ofin J叩an.

PrPSc between two strains of transmissible mink encepha‑lopathy (TME) by proteinase K, and that after digestion, thePrPScfrom one strain Was 10 amino acid residues larger than

4. Transmission process of infectious pr10n and

the PrPSc from the other strain. This differential digestion of

species barrier

PrPSc was noted more仇an a decade ago in s山dies on SAFs

One model fわr the transmission or scrapie hypothesis thatfrom different scrapie strains (3 7). Differences have also been

a prpsc molecule may combine wi仙a PrPC molecule to glVe aobserved in PrPSc between fatal familial insomnia (FFI) andheterodimer. The PrPC molecule is transfわrmed to a PrPSc

familial Creutzfeldt‑Jakob disease (CJD) cases. In this casemolecule, which then goes on to transform other PrPC moleculesofFFI, the PrP isoforms differed in relative abundance of the(1). This model does not exclude the presence ofa nucleic
acid genome within the protein coat. Infectious extracts

glycosylated fわrms and in the protease cleavage site (38)･

Monariet al. Concluded that because FFI and CJD PrP protein
differ only at codon 1 29, that difference alters the conformation
orthe protein (38). These FFI and CJD models rely on theirrespective protein conformations as the basis for differential
targetlng tO different populations of neurons within the brain,enriched with SAP and PrPSc can be partially dena山red andsubjected to SDSIPOlyacrylamide electrophoresis without
significant loss of infectivity (26), indicating that ira nucleic

acid is present, it must be very tightly associatedwith theprotein･Asa further twist, there are reports that infectiv)ty

to produce the characteristic brain lesions associated wi仇thecan be dissociated from the production ofPrPSc (27, 28). Not

individual strainofscrapie (39). TYleSe FFI and CJD results are

all PrPSc appears to be infectious･ There are around 1 05 prpSc

interestlng, but do not necessarily answer all or血e questions

molecules per unit of infectivity (29), and Rubenstein has

posed by strain dete‑ination･
When the scr叩1e agent is passaged in a species ofanimal

perf♭med experiments in which PrPSc is degraded without adifferent from the one in which it has been replaclng, thecorrespondingly )arge decrease in infectivity titers (30)･
The structure or PrP has received much attention due toincubation period is prolonged at the first passage, setting a

the fact that only structural differences have been substantiatednew but predictable length of time on subsequent passages･

between PrPC and PrPSc. The secondary structure and confor‑

This phenomenon is known as the "species barrier" effectmational differences have been studied by Fourier transform(40). Diseases do not always occur a触r inoculation with

infrared, nuorescebnce, and circular dichroism spectroscopy (3 1 ‑scraple‑infected brain homogenates; Some scraple agent33)･ Theヮost powerful way to elucidate the tertiary structurestrains do not produce clinical signs in certain animalspeciesof a proteln at high resolution is by Xィay crystallography,

and other strain畠appear to be specific to a particular species.

but the PrP protein has not yet been crystallized due toAttempts to modify the species barrier by sensltlZlng the new

difficulties in obtainlng Sufficient material and overcomlng

host by exposure,to tissues of the old host befわre inoculation

noncrystalline aggregation effects. At this moment X‑ray

met with only shght effects (40)･ The presen.ce of tissue fromcIyStallogr叩hy does not provide the dぬiled stmcture orpriona different speciesmight cause immunologlCal effects upon

protein. A three‑dimensional (3D) model stmcture of PrP has

inoculation. This immunologlCal effect might be observed, if

been hypothesized by Huang et al. (34). It has been obseⅣed

a post protein formed a part of the infectious agent･ The more

spectroscopically that PrPC is mostly α‑helix, whereas PrPSc

closely related the two species, the smaller the species barrier･The effect would be specir1C and would only affect the firsthas a high β‑sheet component (35).

passage within a different species (41 ).

The most vexlng problems in the hypothesis fわr pr10n

infectivlty are the presence of at least 20 Well characterized
scraple Strains and the ability of these strains to be passaged

5･ Role ofPrPC and PrP‑Jibe protein

through different animal specieswithout alteration of the
incubation period or pathology. The hypothesis for prlOn

Recently, We have established two distinct systems or cell

infectivitysuggests that strain variation is induced by different

tines, One derived from the brain of mice homozygous for58

Transactlng effect of prlOn gene complex

consplCuOuS in仇e medulla oblongata. In J叩aneSe Cases, it

is also evident in the neurons of the thalamus(1 9). Prolifera‑tion of astrocytes is also a conspicuous feature･ By imm.upo‑

Wild type Prnp

Prnd

histochemistry or tissue sections f♭r PrPSc, positive stalnlng

was regularly observed in the hippocampus, thalamus, andmedulla oblongata in our cases (19).
prpc ∫

suppression
7. Preclinical diagnosis of scraple

Knockl0ut type Neorln Japan and Great Britain, WBA is applied to biopsleS Or

Prndlymph nodes (48, 49). Sometimes this is successful for

detecting experimentally or naturally scraple‑affected animals.
In Europe, PrPSc has been immunohistochemically detected

Ataxla prOteln

in tissue sections of the tonsil from affected sheep (50).

apoptosis protein

Our findings indicate that scraple agents Can be detectedfrom the placentae of naturally infected amimals throughFig. 4. Structure and relationship of the Prnp and Prnd genes.

inoculation intomice intracerebrally (24)･ It takes approfi‑
mately 6 months to detect histologlCal lesions in the mlCe
brain. Therefわre, it may become possible to diagnose scraple

disrupted Pmp gene and the other fTrom the brain ofwild‑typeinfectionina large number of sheep by the isolation of thesemice. Cells were immortalized by recombinant retrovirus
vector‑mediated transduction of the SV40 T‑antigen gene. The

transmissibIe agents from the placentae during the preclinicalstagewithout requiring. any surgical procedure (5 1 )･ Recently,

pr10nless cell line shows a short neurite extension in com‑capillary electrophoresIS Was used to detect PrPSc in the blood

parison with wild type cell hne after treatment with phorbo1

from naturally infected sheep, for prechnical diagnosis (52).

I 2‑myristate I 3‑acetate (PMA). Thewild type cell line survived
in serum‑free medium with or without PMA, whereas the

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