Several studies have shown that transmission of natural scrapie can occur vertically and horizontally, and that variations in scrapie incidence between and within infected flocks are mostly due to differences in the proportion of sheep with susceptible and resistant PRNP genotypes. This report presents the results of a 12-year period of scrapie monitoring in a closed flock of Suffolk sheep, in which only animals of the ARQ/ARQ genotype developed disease. Among a total of 120 of these, scrapie attack rates varied between birth cohorts from 62.5 % (5/8) to 100 % (9/9), and the incidence of clinical disease among infected sheep from 88.9 % (8/9) to 100 % (in five birth cohorts). Susceptible sheep born to scrapie-infected ewes showed a slightly higher risk of becoming infected (97.2 %), produced earlier biopsy-positive results (mean 354 days) and developed disease at a younger age (median 736 days) than those born to non-infected dams (80.3 %, 451 and 782 days, respectively). Taken together, this was interpreted as evidence of maternal transmission. However, it was also observed that, for the birth cohorts with the highest incidence of scrapie (90–100 %), sheep born to infected and non-infected dams had a similar risk of developing scrapie (97.1 and 95.3 %, respectively). Compared with moderate-attack-rate cohorts (62.5–66.7 %), high-incidence cohorts had greater numbers of susceptible lambs born to infected ewes, suggesting that increased rates of horizontal transmission in these cohorts could have been due to high levels of environmental contamination caused by infected placentas.
AndréolettiO.,
LacrouxC.,
ChabertA.,
MonnereauL.,
TabouretG.,
LantierF.,
BerthonP.,
EychenneF.,
Lafond-BenestadS.other authors2002; PrPSc accumulation in placentas of ewes exposed to natural scrapie: influence of foetal PrP genotype and effect on ewe-to-lamb transmission. J Gen Virol 83:2607–2616[PubMed]
BeltP. B. G. M.,
MuilemanI. H.,
SchreuderB. E. C.,
Bos-de RuijterJ.,
GielkensA. L. J.,
SmitsM. A.1995; Identification of five allelic variants of the sheep PrP gene and their association with natural scrapie. J Gen Virol 76:509–517 [View Article][PubMed]
ClouscardC.,
BeaudryP.,
ElsenJ. M.,
MilanD.,
DussaucyM.,
BounneauC.,
SchelcherF.,
ChatelainJ.,
LaunayJ. M.,
LaplancheJ. L.1995; Different allelic effects of the codons 136 and 171 of the prion protein gene in sheep with natural scrapie. J Gen Virol 76:2097–2101 [View Article][PubMed]
ElsenJ.-M.,
AmiguesY.,
SchelcherF.,
DucrocqV.,
AndreolettiO.,
EychenneF.,
Tien KhangJ. V.,
PoiveyJ.-P.,
LantierF.,
LaplancheJ.-L.1999; Genetic susceptibility and transmission factors in scrapie: detailed analysis of an epidemic in a closed flock of Romanov sheep. Arch Virol 144:431–445 [View Article][PubMed]
FosterJ.,
McKenzieC.,
ParnhamD.,
DrummondD.,
GoldmannW.,
StevensonE.,
HunterN.2006; Derivation of a scrapie-free sheep flock from the progeny of a flock affected by scrapie. Vet Rec 159:42–45 [View Article][PubMed]
GonzálezL.,
MartinS.,
Begara-McGorumI.,
HunterN.,
HoustonF.,
SimmonsM.,
JeffreyM.2002; Effects of agent strain and host genotype on PrP accumulation in the brain of sheep naturally and experimentally affected with scrapie. J Comp Pathol 126:17–29 [View Article][PubMed]
GonzálezL.,
DagleishM. P.,
BellworthyS. J.,
SisóS.,
StackM. J.,
ChaplinM. J.,
DavisL. A.,
HawkinsS. A. C.,
HughesJ.,
JeffreyM.2006; Postmortem diagnosis of preclinical and clinical scrapie in sheep by the detection of disease-associated PrP in their rectal mucosa. Vet Rec 158:325–331 [View Article][PubMed]
GonzálezL.,
DagleishM. P.,
MartinS.,
DexterG.,
SteeleP.,
FinlaysonJ.,
JeffreyM.2008; Diagnosis of preclinical scrapie in live sheep by the immunohistochemical examination of rectal biopsies. Vet Rec 162:397–403 [View Article][PubMed]
HamiltonS.,
FinlaysonJ.,
PangY.,
BuxtonD.,
EatonS.,
SteeleP.,
DagleishM.,
BenavidesJ.,
GonzálezL.other authors2008; PrPsc distribution in perfused placentas from Suffolk sheep naturally infected with scrapie. In: Proceedings of Prion 2008 Conference, 8–10 October 2008, Madrid, Spain, p. 82
HealyA. M.,
HannonD.,
MorganK. L.,
WeaversE.,
CollinsJ. D.,
DohertyM. L.2004; A paired case–control study of risk factors for scrapie in Irish sheep flocks. Prev Vet Med 64:73–83 [View Article][PubMed]
HoinvilleL. J.,
TongueS. C.,
WilesmithJ. W.2010; Evidence for maternal transmission of scrapie in naturally affected flocks. Prev Vet Med 93:121–128 [View Article][PubMed]
HourriganJ.,
KlingspornA.,
ClarkW. W.,
DeCampM.1979; Epidemiology of scrapie in the United States. In Slow Transmissible Diseases of the Nervous System pp. 331–356 Edited by
PrusinerS. B.,
HadlowW. B.
New York: Academic Press;
HunterN.,
GoldmannW.,
SmithG.,
HopeJ.1994; The association of a codon 136 PrP gene variant with the occurrence of natural scrapie. Arch Virol 137:171–177 [View Article][PubMed]
HunterN.,
MooreL.,
HosieB. D.,
DingwallW. S.,
GreigA.1997; Association between natural scrapie and PrP genotype in a flock of Suffolk sheep in Scotland. Vet Rec 140:59–63 [View Article][PubMed]
IkedaT.,
HoriuchiM.,
IshiguroN.,
MuramatsuY.,
Kai-UweG. D.,
ShinagawaM.1995; Amino acid polymorphisms of PrP with reference to onset of scrapie in Suffolk and Corriedale sheep in Japan. J Gen Virol 76:2577–2581 [View Article][PubMed]
JeffreyM.,
MartinS.,
ThomsonJ. R.,
DingwallW. S.,
Begara-McGorumI.,
GonzálezL.2001; Onset and distribution of tissue PrP accumulation in scrapie-affected Suffolk sheep as demonstrated by sequential necropsies and tonsillar biopsies. J Comp Pathol 125:48–57 [View Article][PubMed]
MaddisonB. C.,
ReesH. C.,
BakerC. A.,
TaemaM.,
BellworthyS. J.,
ThorneL.,
TerryL. A.,
GoughK. C.2010; Prions are secreted into the oral cavity in sheep with preclinical scrapie. J Infect Dis 201:1672–1676 [View Article][PubMed]
RedmanC. A.,
CoenP. G.,
MatthewsL.,
LewisR. M.,
DingwallW. S.,
FosterJ. D.,
Chase-ToppingM. E.,
HunterN.,
WoolhouseM. E. J.2002; Comparative epidemiology of scrapie outbreaks in individual sheep flocks. Epidemiol Infect 128:513–521 [View Article][PubMed]
SaundersG. C.,
LantierI.,
CawthrawS.,
BerthonP.,
MooreS. J.,
ArnoldM. E.,
WindlO.,
SimmonsM. M.,
AndréolettiO.other authors2009; Protective effect of the T112 PrP variant in sheep challenged with bovine spongiform encephalopathy. J Gen Virol 90:2569–2574 [View Article][PubMed]
SisóS.,
JeffreyM.,
SteeleP.,
McGovernG.,
MartinS.,
FinlaysonJ.,
ChianiniF.,
GonzálezL.2008; Occurrence and cellular localization of PrPd in kidneys of scrapie-affected sheep in the absence of inflammation. J Pathol 215:126–134 [View Article][PubMed]
SisóS.,
JeffreyM.,
GonzálezL.2009; Neuroinvasion in sheep transmissible spongiform encephalopathies: the role of the haematogenous route. Neuropathol Appl Neurobiol 35:232–246 [View Article][PubMed]
TouzeauS.,
Chase-ToppingM. E.,
MatthewsL.,
LajousD.,
EychenneF.,
HunterN.,
FosterJ. D.,
SimmG.,
ElsenJ. M.,
WoolhouseM. E. J.2006; Modelling the spread of scrapie in a sheep flock: evidence for increased transmission during lambing seasons. Arch Virol 151:735–751 [View Article][PubMed]
VaccariG.,
ScaviaG.,
SalaM.,
CossedduG.,
ChiappiniB.,
ConteM.,
EspositoE.,
LorenzettiR.,
PerfettiG.other authors2009; Protective effect of the AT137RQ and ARQK176 PrP allele against classical scrapie in Sarda breed sheep. Vet Res 40:19 [View Article][PubMed]
WestawayD.,
ZulianiV.,
CooperC. M.,
Da CostaM.,
NeumanS.,
JennyA. L.,
DetwilerL.,
PrusinerS. B.1994; Homozygosity for prion protein alleles encoding glutamine-171 renders sheep susceptible to natural scrapie. Genes Dev 8:959–969 [View Article][PubMed]