Surveillance and simulation of bovine spongiform encephalopathy and scrapie in small ruminants in Switzerland.
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.
Häusermann
Chantal
C
NeuroCenter, Reference Laboratory for TSE in animals, Department of Clinical Research and Veterinary Public Health, Vetsuisse Faculty, University of Berne, Switzerland.
Schwermer
Heinzpeter
H
Oevermann
Anna
A
Nentwig
Alice
A
Zurbriggen
Andreas
A
Heim
Dagmar
D
Seuberlich
Torsten
T
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
Acta Neuropathol. 2008 Nov;116(5):547-59
18797889
Vet Rec. 1988 Dec 17;123(25):638-44
3218047
Math Biosci. 2000 Dec;168(2):117-35
11121561
Prev Vet Med. 2005 Feb;67(2-3):143-56
15737428
Schweiz Arch Tierheilkd. 2001 Nov;143(11):539-47
11727673
Epidemiol Infect. 2009 Jun;137(6):787-91
19351431
BMC Vet Res. 2008 Apr 02;4:13
18384678
Proc Biol Sci. 1998 Jul 7;265(1402):1205-10
9699313
Vet Res. 2008 Jul-Aug;39(4):19
18187032
Blood. 2008 Dec 1;112(12):4739-45
18647958
Epidemiol Infect. 2006 Apr;134(2):359-67
16490141
J Gen Virol. 2006 Dec;87(Pt 12):3729-3736
17098991
Vet Rec. 2005 Apr 16;156(16):523-4
15833975
Vet Rec. 2003 Aug 16;153(7):202-8
12956297
Trends Microbiol. 2001 Jun;9(6):260-1
11430321
J Gen Virol. 2007 Dec;88(Pt 12):3486-3492
18024920
Acta Neuropathol. 2002 Sep;104(3):279-86
12172914
Schweiz Arch Tierheilkd. 1991;133(2):53-7
2047831
Nat Med. 2000 Mar;6(3):258-9
10700223
Vet Rec. 2005 Aug 13;157(7):206
16100373
Epidemiol Infect. 2003 Oct;131(2):1015-22
14596544
Schweiz Arch Tierheilkd. 2006 Jul;148(7):341-2, 344-8
16888920
J Gen Virol. 2006 Jul;87(Pt 7):2099-2107
16760414
Emerg Infect Dis. 2009 Aug;15(8):1214-21
19751582
Vet Rec. 1993 Oct 2;133(14):339-41
8236676
Vet J. 2010 Sep;185(3):338-40
19635675
EMBO J. 2006 Jun 21;25(12):2674-85
16724107
Nature. 2002 Jan 24;415(6870):420-4
11786878
Math Biosci. 1998 Nov;153(2):79-98
9825634
Nature. 1997 Oct 2;389(6650):498-501
9333239
J Vet Diagn Invest. 2009 Jan;21(1):97-101
19139507
J Comp Pathol. 2001 Nov;125(4):271-84
11798244
BMC Vet Res. 2009 Feb 10;5:8
19208228
BMC Vet Res. 2008 Jun 10;4:19
18544152
J Infect Dis. 1998 Oct;178(4):949-53
9806020
J Virol Methods. 2004 Apr;117(1):27-36
15019257
BMC Vet Res. 2007 Feb 13;3:2
17298670
J Virol. 2008 Oct;82(20):9839-47
18684809
BMC Vet Res. 2007 Aug 28;3:20
17725818
J Gen Virol. 2006 Dec;87(Pt 12):3737-3740
17098992
Vet Rec. 2003 Mar 8;152(10):298-9
12650473
Nature. 1996 Oct 24;383(6602):685-90
8878476
Science. 2002 Jan 11;295(5553):332-5
11719694
Nat Med. 2005 Nov;11(11):1137-8
16270061
Schweiz Arch Tierheilkd. 1982 May;124(5):227-32
7201673
Science. 1991 Jun 14;252(5012):1515-22
1675487
Lancet. 1996 Apr 6;347(9006):921-5
8598754
J Vet Diagn Invest. 2005 Nov;17(6):509-27
16475509
Berl Munch Tierarztl Wochenschr. 2007 May-Jun;120(5-6):189-96
17555037
Schweiz Arch Tierheilkd. 2005 Oct;147(10):435-43
16259409
PLoS Pathog. 2007 Jun;3(6):e82
17559305
Trends Microbiol. 2001 Feb;9(2):67-70
11173245
J Vet Diagn Invest. 2007 Jan;19(1):2-8
17459826