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From: TSS ()
Subject: Re: SCRAPIE USA UPDATE MARCH - JUNE 2005
Date: August 30, 2005 at 10:15 am PST
In Reply to: SCRAPIE USA UPDATE MARCH - JUNE 2005 posted by TSS on August 24, 2005 at 7:03 pm:
Veterinary Services
Centers for Epidemiology and Animal Health March 2004
____________________________________________________________________________
_____________________________________________
Highlights of Phase II: Scrapie:
Ovine Slaughter Surveillance
Study 2002-2003
The purpose of the SOSS study was to estimate
the regional and national prevalence of scrapie in
mature cull sheep in the United States.
Phase I of SOSS was conducted from February
2001 through March 2002 and included refinement
of the study design and sample collection training.
The purpose of Phase I was to develop and modify
the sample collection and testing processes,
without emphasizing statistical results.
SOSS Phase II is similar to Phase I in that
sample collection procedures and testing were
used, along with a representative sample
allocation. Beginning April 1, 2002, and continuing
through March 31, 2003, Phase II included the
collection of tissue samples from 12,508 sheep
from 22 slaughter plants throughout the United
States (21 FSIS inspected, 1 State plant) and 1
large livestock market in Texas. The 21 FSIS plants
represented approximately two-thirds of the total
FSIS mature sheep slaughtered during the study
period. The livestock market represented
approximately one-half of the live sheep exported
to Mexico. All sample data were statistically
weighted to reflect the population from which the
sample was selected. The number of samples
collected from each plant on a specific day was
statistically weighted to represent the volume of
mature sheep slaughtered (sold) through each
plant (market) that specific day. This weight was
adjusted for the total volume of mature sheep
through the plant (market) from April 2002 through
March 2003. Within each facility sample collectors
were instructed to collect samples using systematic
sampling. Overall, the samples collected from the
22 plants and the livestock market represented
299,000 sheep (54 percent of the cull sheep
population, estimated at 550,000 head).
Sheep were traced to State of origin based on
ear tags and/or other information obtained by the
collector at the plant or market. For analysis
purposes, samples identified to individual States
were assigned to one of four defined regions.
Sometimes only a listing of multiple States could be
obtained for a group of sheep (e.g., market animals
accumulated across numerous States). These
samples were assigned to the Multiregion category
if the States they came from were not all in the
same region. In cases where a trace State was not
identified by the collector (n = 2,020), a region was
assigned based on their official identification
information. The 2001 NAHMS Sheep study
showed that at least 95 percent of cull sheep
movement was within the region of origin. Out of
the 12,508 samples submitted, all but 2,127 were
identified to a unique region (Table 1).
Table 1. Number of Samples Submitted, by Face Color
and By Region.
Samples Submitted
Region
Face
Color West Mountain Central East
Multiregion
Total
Black 100 535 680 1,023 453 2,791
White 493 2,997 1,993 1,283 1,472 8,238
Mottled 71 305 413 404 194 1,387
Unknown 6 32 4 42 8 92
Total 670 3,869 3,090 2,752 2,127 12,508
Obex, tonsil, and lymph-node tissues from each
sheep were tested using the immunohistochemistry
(IHC) technique at the National Veterinary Services
Laboratory. A positive case was defined as having
a positive test result on any tissue.
United States Department of Agriculture • Animal and Plant Health Inspection
Service • Safeguarding American Agriculture
Prior to the SOSS study, the estimated
pre as 0.07
p ’96
spected
’96
hlights were excerpted from
Pha
revalence estimates
Of the 12,508 mature sheep sampled, valid (at
itive
0.20
s
.
Three tissue types (obex, tonsil, and
llected
in
s
valence of scrapie in the United States w
percent (based on unpublished data from the
NAHMS Sheep ’96 study). However, the Shee
estimate was based on a mail-in survey of
producers who reported the presence of su
or confirmed cases of scrapie in their flock over a
period of 5 years, including lambs and mature
sheep. The flock estimate was then expanded
based on flock size to generate the animal-leve
prevalence estimate. The results of the SOSS
study cannot be directly compared to the Sheep
prevalence estimate because of differences in
study design, reference population, and data
collection methods.
The following hig
l
se II: Scrapie: Ovine Slaughter Surveillance
Study 2002-2003.
P
•
least one testable tissue) test results were
obtained from 12,491 (99.9 percent). A pos
result was recorded for any animal that tested
positive by IHC on one or more of the tissues
sampled. The overall weighted national
prevalence of scrapie in mature sheep is
percent. Estimates could not be made in the
West region due to the low number of sample
obtained. However, national estimates include
samples collected in the West region (Figure 1)
•
retropharyngeal lymph node) were co
from each sheep head for IHC testing. As
expected, each tissue type differed slightly
the number tested as well as the number of
positive results; however, the prevalence wa
similar for the three tissue types (Figure 2).
0.0
0.2
0.4
0.6
Figure 2. Percent of Sheep That Tested Positive for Scrapie,
by Tissue Type
Percent
Tissue Type
Obex Tonsil Retropharyngeal
lymph node
0.18 0.19 0.20
Scrapie prevalence (one or more tissue
lack-
ot
•
samples tested positive) was highest in b
faced sheep (0.84 percent). White-faced sheep
were far less likely to test positive for scrapie
(less than 0.01 percent). Some animals were
presented for sample collection with the skin
removed. Therefore, face color could not be
determined on these animals and they were n
included in these estimates (Figure 3).
West Mountain Central East
United States Department of Agriculture • Animal and Plant Health Inspection
Service • Safeguarding American Agriculture
0.0
0.2
0.4
0.6
0.8
1.0
Percent
Face Color
Figure 3. Percent of Sheep That Tested Positive for Scrapie,
by Face Color
0.00
0.84
0.12
White Black Mottled
p
t of
,
Age was determined based on the number of
•• visible permanent incisors. Four-year-old shee
tested positive (one or more tissue samples
tested positive) most frequently (0.49 percen
sheep tested). Scrapie prevalence increased
with age until the animals reached 4 years old
then decreased (Figure 4).
0.0
0.5
1.0
1.5
2.0
Black-faced sheep
National
Figure 4. Percent of Sheep That Tested Positive for Scrapie
(National and Black-faced Sheep), by Age
Percent
Age
0.11
0.00
0.21
0.54 0.49
1.77
0.13
0.69
1 and 2 years 3 years 4 years 5 years or more
enetics
ue samples from the 33 sheep that tested
pos
e at
______________________________
or more information, contact:
E7
G
Tiss
itive for scrapie were submitted for genetic
testing. All 33 samples were of the QQ genotyp
codon 171. This genotype has been characterized
as the least resistant to scrapie.
__
F
SDA:APHIS:VS:CEAH U
NRRC Building B, M.S. 2
2150 Centre Avenue
-8117 Fort Collins, CO 80526
970.494.7000
web@aphis.usda.gov E-mail: NAHMS
www.aphis.usda.gov/vs/ceah/cahm
N421.0304 #
____________________________________
) prohibits discrimination in
plaint of discrimination, write USDA, Director, Office of
yer.
ention of companies or commercial products does not imply
s nor
he U.S. Department of Agriculture (USDA T
all its programs and activities on the basis of race, color, national
origin, sex, religion, age, disability, political beliefs, sexual
orientation,
or marital status or family status. (Not all prohibited bases apply to all
programs.) Persons with disabilities who require alternative means for
communication of program information (Braille, large print, audiotape,
etc.) should contact USDA’s TARGET Center at (202) 720-2600 (voice
and TDD).
o file a com T
Civil Rights, Room 326-W, Whitten Building, 1400 Independence
Avenue, SW, Washington, DC 20250-9410 or call (202) 720-5964
(voice and TDD). USDA is an equal opportunity provider and emplo
M
recommendation or endorsement by the U.S. Department of
Agriculture over others not mentioned. USDA neither guarantee
warrants the standard of any product mentioned. Product names are
mentioned solely to report factually on available data and to provide
specific information.
United States Department of Agriculture • Animal and Plant Health Inspection
Service • Safeguarding American Agriculture
http://www.aphis.usda.gov/vs/ceah/ncahs/nahms/sheep/SOSS_highlights.pdf
Animal and
Plant Health
Inspection
SOSS
Phase II: Scrapie: Ovine Slaughter Surveillance
Study 2002-2003
snip... Section I: Prevalence Estimates
A. Weighted Test
Results
1. Overall prevalence
Of the 12,508 mature sheep sampled, valid (at least one testable tissue)
test
results were obtained from 12,491 (99.9 percent). A positive result was
recorded for any animal that tested positive by immunohistochemistry (IHC)
on
one or more of the tissues sampled. The overall weighted national
prevalence of scrapie in mature sheep is 0.20 percent. Estimates could not
be
made in the West region due to the low number of samples obtained. However,
national estimates include samples collected in the West region.
a. Percentage of sheep that tested positive for scrapie, by region*:
Percent Sheep
Region
Mountain Central East Multiregion National
Pct.
Std.
Error Pct.
Std.
Error Pct.
Std.
Error Pct.
Std.
Error Pct.
Std.
Error
0.14 (0.06) 0.21 (0.10) 0.52 (0.15) 0.13 (0.07) 0.20 (0.04)
*Because of the low number of samples obtained in the West region, results
for the
West region are included in the National estimates but are not listed
individually. snip...
http://www.aphis.usda.gov/vs/ceah/ncahs/nahms/sheep/SOSSphase2.pdf
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