Veterinary Services 

Centers for Epidemiology and Animal Health March 2003 

_______________________________________________________________________________________________________________________________________ 

Scrapie: Ovine Slaughter 

Surveillance — Phase I 

Overview 

The overall objective of the Scrapie: Ovine 

Slaughter Surveillance (SOSS) study is to estimate 

the national and regional prevalence of scrapie in 

mature cull sheep entering slaughter channels. The 

study was initiated at the request of members of the 

sheep industry, who wanted to accelerate 

eradication of the disease. 

Beginning in February 2001 and ending in 

March 2002, Phase I included the study design, 

methods development, and sample-collection 

training. The objective of Phase I was to develop 

and modify the sample collection and testing 

processes, without emphasizing statistical results. 

Phase II, which is the actual prevalence study, 

started April 1, 2002, and will continue for 

approximately 1 year. The number of samples to be 

collected from each participating plant on a weekly 

or bi-weekly basis was determined based on the 

number of cull ewes killed at the plant in 2001. 

Phase III will evaluate and analyze data received 

during Phase II. Phase III results will be published 

in fall 2003. 

Phase I Methods 

The slaughter plants selected to participate in 

SOSS Phase I were identified based on historical 

slaughter data obtained through the Food Safety 

and Inspection Service and the National 

Agricultural Statistics Service. Since the currently 

accepted diagnostics are for adult animals, plants 

that slaughtered large numbers of mature cull ewes 

were targeted for the SOSS study. 

Coordinators and sample collectors were 

selected for each State with a participating plant. 

Coordinators served as primary contacts in their 

States and were responsible for ensuring that the 

correct number of quality samples were submitted, 

supplies were ordered and provided to collection 

personnel, and information was disseminated as 

needed. Sample collectors were responsible for the 

actual collection of tissues at the slaughter plants. 

Training the sample collectors was a critical 

component of SOSS Phase I and was 

accomplished via hands-on instruction and a 

Procedures Manual that identified the specific 

anatomical locations of the needed tissues. As the 

study progressed, regular field reports were 

produced to inform collectors of the quality of their 

submitted samples. 

Established goals for submitting proper tissue in 

desirable condition were defined and met prior to 

Phase II of the study. 

Diagnostic laboratories were contracted by the 

National Veterinary Services Laboratory (NVSL). 

Three contract labs were used for Phase I. Before 

SOSS tissues were submitted, laboratory personnel 

were trained and the labs were approved by NVSL. 

To remain consistent with Phase I objectives, 

convenience sampling, which is sampling at will 

and without regard to randomness, was used for all 

samples taken during Phase I. 

A standard kit was used that included tools and 

materials to collect, package, and ship the needed 

tissues to NVSL. 

Samples were collected from the brainstem 

(obex), cerebellum, both tonsils, both 

retropharyngeal lymph nodes, and the lymphoid 

tissue of the third eyelid. 

At the time of tissue collection, data regarding 

each head were recorded on a submission form. 

These data included a unique sample number, 

animal identification, face color, and age of the 

animal based on the number and condition of 

permanent teeth. Ear tags and plant or market 

records (when available), and the Veterinary 

Services generic data base were used to determine 

the region of animal origin. 

Phase I Findings 

SOSS Phase I was a “pilot” project. Samples 

were not collected with the intention of performing 

rigorous statistical analysis. Therefore, results 

shown below do not reflect the U.S. cull ewe 

population. 
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Tissue samples were collected from 1,159 cull 

ewes in 23 slaughter plants from 13 States. 

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Sheep Face 

Color Number Percent 

White 648 55.9 

Black 318 27.4 

Mottled 143 12.4 

Not recorded 50 4.3 

 Total 1,159 100.0 

Age of Sheep Number Percent 

1 year 54 4.7 

2 years 127 10.9 

3 years 201 17.3 

4 years 407 35.1 

5 years or older 338 29.2 

Not recorded 32 2.8 

 Total 1,159 100.0 

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Tissues were tested using the 

immunohistochemistry technique (IHC). 

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Tissue Test 

Result (IHC) Obex Tonsil 

Lymph 

Node 

Negative 1,079 939 1,139 

Positive 2 2 2 

Untestable 78 218 18 

 Total 1,159 1,159 1,159 

_____________________ 

For more information, contact: 

USDA:APHIS:VS:CEAH 

NRRC Building B., M.S. 2E7 

2150 Centre Avenue 

Fort Collins, CO 80526-8117 

970.494.7000 

E-mail: NAHMSweb@aphis.usda.gov 

www.aphis.usda.gov/vs/ceah/cahm

#N390.0303 

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Genotype results were obtained for 611 of the 

1,159 samples. 

 _________________________________________________ 

Genotype Results Number Percent

QQ 237 20.4 

QR 279 24.1 

RR 95 8.2 

XX (not testable) 44 3.8 

Not tested 504 43.5 

Total 1,159 100.0 

Two animals out of the 1,159 tested were 

positive for scrapie. In these animals, all three 

tissues (obex, tonsil, and lymph node) tested 

positive. Both were 4-year-old ewes and were QQ 

genotypes. One was white -faced, the other blackfaced. Neither sample could be identified back to 

the region of origin. 

Lessons Learned 

Phase I allowed for the development of plant 

relations, modification of forms, and the fine-tuning 

of tissue collection protocols before the 

implementation of the full study in April of 2002. 

Since approximately two-thirds of all mature cull 

ewes are exported to Mexico annually, a livestock 

market sampling protocol was developed for Phase 

II that calls for the sampling of sheep that are 

typically exported to Mexico and not sent to 

domestic slaughter plants. 

An instructional CD-ROM containing video 

clips, color pictures, and the SOSS instruction 

manual was developed and distributed for Phase II. 

By the time Phase II began, proficiency (percent 

testable tissues) for each tissue type was at least 

80 percent. 

Collecting third eyelid tissue from dead animals 

was extremely difficult and was stopped a few 

months into Phase I. 

Additional diagnostic laboratories were 

contracted by NVSL to assist with the increased 

workload during Phase II. 

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