title: Surveillance and simulation of bovine spongiform encephalopathy and scrapie in small ruminants in Switzerland.
abstract: BACKGROUND
  After bovine spongiform encephalopathy (BSE) emerged in European cattle livestock in 1986 a fundamental question was whether the agent established also in the small ruminants' population. In Switzerland transmissible spongiform encephalopathies (TSEs) in small ruminants have been monitored since 1990. While in the most recent TSE cases a BSE infection could be excluded, for historical cases techniques to discriminate scrapie from BSE had not been available at the time of diagnosis and thus their status remained unclear. We herein applied state-of-the-art techniques to retrospectively classify these animals and to re-analyze the affected flocks for secondary cases. These results were the basis for models, simulating the course of TSEs over a period of 70 years. The aim was to come to a statistically based overall assessment of the TSE situation in the domestic small ruminant population in Switzerland.
  
  
  RESULTS
  In sum 16 TSE cases were identified in small ruminants in Switzerland since 1981, of which eight were atypical and six were classical scrapie. In two animals retrospective analysis did not allow any further classification due to the lack of appropriate tissue samples. We found no evidence for an infection with the BSE agent in the cases under investigation. In none of the affected flocks, secondary cases were identified. A Bayesian prevalence calculation resulted in most likely estimates of one case of BSE, five cases of classical scrapie and 21 cases of atypical scrapie per 100'000 small ruminants. According to our models none of the TSEs is considered to cause a broader epidemic in Switzerland. In a closed population, they are rather expected to fade out in the next decades or, in case of a sporadic origin, may remain at a very low level.
  
  
  CONCLUSIONS
  In summary, these data indicate that despite a significant epidemic of BSE in cattle, there is no evidence that BSE established in the small ruminant population in Switzerland. Classical and atypical scrapie both occur at a very low level and are not expected to escalate into an epidemic. In this situation the extent of TSE surveillance in small ruminants requires reevaluation based on cost-benefit analysis.
authors.affiliation: NeuroCenter, Reference Laboratory for TSE in animals, Department of Clinical Research and Veterinary Public Health, Vetsuisse Faculty, University of Berne, Switzerland.
authors.forename: Chantal
authors.initials: C
authors.lastname: Häusermann
authors.forename: Heinzpeter
authors.initials: H
authors.lastname: Schwermer
authors.forename: Anna
authors.initials: A
authors.lastname: Oevermann
authors.forename: Alice
authors.initials: A
authors.lastname: Nentwig
authors.forename: Andreas
authors.initials: A
authors.lastname: Zurbriggen
authors.forename: Dagmar
authors.initials: D
authors.lastname: Heim
authors.forename: Torsten
authors.initials: T
authors.lastname: Seuberlich
mesh_terms: D000818:Animals; D001921:Brain / Q000473:pathology; D002417:Cattle; D003198:Computer Simulation; D016643:Encephalopathy, Bovine Spongiform / Q000453:epidemiology* / Q000473:pathology; D015511:Goat Diseases / Q000453:epidemiology* / Q000473:pathology; D006041:Goats; D008954:Models, Biological; D011159:Population Surveillance; D012608:Scrapie / Q000453:epidemiology* / Q000473:pathology; D012756:Sheep; D013557:Switzerland / Q000453:epidemiology; D013997:Time Factors
references.citation: Acta Neuropathol. 2008 Nov;116(5):547-59
references.pmid: 18797889
references.citation: Vet Rec. 1988 Dec 17;123(25):638-44
references.pmid: 3218047
references.citation: Math Biosci. 2000 Dec;168(2):117-35
references.pmid: 11121561
references.citation: Prev Vet Med. 2005 Feb;67(2-3):143-56
references.pmid: 15737428
references.citation: Schweiz Arch Tierheilkd. 2001 Nov;143(11):539-47
references.pmid: 11727673
references.citation: Epidemiol Infect. 2009 Jun;137(6):787-91
references.pmid: 19351431
references.citation: BMC Vet Res. 2008 Apr 02;4:13
references.pmid: 18384678
references.citation: Proc Biol Sci. 1998 Jul 7;265(1402):1205-10
references.pmid: 9699313
references.citation: Vet Res. 2008 Jul-Aug;39(4):19
references.pmid: 18187032
references.citation: Blood. 2008 Dec 1;112(12):4739-45
references.pmid: 18647958
references.citation: Epidemiol Infect. 2006 Apr;134(2):359-67
references.pmid: 16490141
references.citation: J Gen Virol. 2006 Dec;87(Pt 12):3729-3736
references.pmid: 17098991
references.citation: Vet Rec. 2005 Apr 16;156(16):523-4
references.pmid: 15833975
references.citation: Vet Rec. 2003 Aug 16;153(7):202-8
references.pmid: 12956297
references.citation: Trends Microbiol. 2001 Jun;9(6):260-1
references.pmid: 11430321
references.citation: J Gen Virol. 2007 Dec;88(Pt 12):3486-3492
references.pmid: 18024920
references.citation: Acta Neuropathol. 2002 Sep;104(3):279-86
references.pmid: 12172914
references.citation: Schweiz Arch Tierheilkd. 1991;133(2):53-7
references.pmid: 2047831
references.citation: Nat Med. 2000 Mar;6(3):258-9
references.pmid: 10700223
references.citation: Vet Rec. 2005 Aug 13;157(7):206
references.pmid: 16100373
references.citation: Epidemiol Infect. 2003 Oct;131(2):1015-22
references.pmid: 14596544
references.citation: Schweiz Arch Tierheilkd. 2006 Jul;148(7):341-2, 344-8
references.pmid: 16888920
references.citation: J Gen Virol. 2006 Jul;87(Pt 7):2099-2107
references.pmid: 16760414
references.citation: Emerg Infect Dis. 2009 Aug;15(8):1214-21
references.pmid: 19751582
references.citation: Vet Rec. 1993 Oct 2;133(14):339-41
references.pmid: 8236676
references.citation: Vet J. 2010 Sep;185(3):338-40
references.pmid: 19635675
references.citation: EMBO J. 2006 Jun 21;25(12):2674-85
references.pmid: 16724107
references.citation: Nature. 2002 Jan 24;415(6870):420-4
references.pmid: 11786878
references.citation: Math Biosci. 1998 Nov;153(2):79-98
references.pmid: 9825634
references.citation: Nature. 1997 Oct 2;389(6650):498-501
references.pmid: 9333239
references.citation: J Vet Diagn Invest. 2009 Jan;21(1):97-101
references.pmid: 19139507
references.citation: J Comp Pathol. 2001 Nov;125(4):271-84
references.pmid: 11798244
references.citation: BMC Vet Res. 2009 Feb 10;5:8
references.pmid: 19208228
references.citation: BMC Vet Res. 2008 Jun 10;4:19
references.pmid: 18544152
references.citation: J Infect Dis. 1998 Oct;178(4):949-53
references.pmid: 9806020
references.citation: J Virol Methods. 2004 Apr;117(1):27-36
references.pmid: 15019257
references.citation: BMC Vet Res. 2007 Feb 13;3:2
references.pmid: 17298670
references.citation: J Virol. 2008 Oct;82(20):9839-47
references.pmid: 18684809
references.citation: BMC Vet Res. 2007 Aug 28;3:20
references.pmid: 17725818
references.citation: J Gen Virol. 2006 Dec;87(Pt 12):3737-3740
references.pmid: 17098992
references.citation: Vet Rec. 2003 Mar 8;152(10):298-9
references.pmid: 12650473
references.citation: Nature. 1996 Oct 24;383(6602):685-90
references.pmid: 8878476
references.citation: Science. 2002 Jan 11;295(5553):332-5
references.pmid: 11719694
references.citation: Nat Med. 2005 Nov;11(11):1137-8
references.pmid: 16270061
references.citation: Schweiz Arch Tierheilkd. 1982 May;124(5):227-32
references.pmid: 7201673
references.citation: Science. 1991 Jun 14;252(5012):1515-22
references.pmid: 1675487
references.citation: Lancet. 1996 Apr 6;347(9006):921-5
references.pmid: 8598754
references.citation: J Vet Diagn Invest. 2005 Nov;17(6):509-27
references.pmid: 16475509
references.citation: Berl Munch Tierarztl Wochenschr. 2007 May-Jun;120(5-6):189-96
references.pmid: 17555037
references.citation: Schweiz Arch Tierheilkd. 2005 Oct;147(10):435-43
references.pmid: 16259409
references.citation: PLoS Pathog. 2007 Jun;3(6):e82
references.pmid: 17559305
references.citation: Trends Microbiol. 2001 Feb;9(2):67-70
references.pmid: 11173245
references.citation: J Vet Diagn Invest. 2007 Jan;19(1):2-8
references.pmid: 17459826