Challenges of Scrapie Eradication

Gary Svetlik, DVM, USDA, APHIS, VS

Scrapie has been present in the United States since 1947 when it was introduced in animals imported from Canada. Efforts to eliminate the disease have not been successful by using flock depopulation and bloodline tracing. The American Sheep Institute has identified scrapie to be a major impairment for sheep producers to be competitive in the world marketplace. USDA, APHIS, VS has published new regulations to eradicate scrapie from our national flock. The regulation requires identification of sheep moving in interstate commerce and provides funds for the destruction of infected and exposed animals. The regulations also establish standards for the handling of flocks identified to be infected or exposed to scrapie.

Scrapie reduces the productivity of flocks and in recent years has created a negative impact on sales of sheep and sheep products. Most renderers will not accept offal from slaughter establishments unless they remove the head of animals over 18 months of age from the raw materials. The disposal of the heads causes added expense to slaughter establishments. Producers whose flock is found to be infected are also negatively impacted by the disease.

Recently we confirmed scrapie in a large club lamb producer’s flock in Texas. The economic and emotional impact to the owner was large. The flock was depopulated at the request of the owner following an epidemiological investigation which indicated that the flock had been infected for a number of years.

Arrangements to dispose of the animals on the premise were made because no one would accept scrapie exposed animals at slaughter. Tissue samples were collected from all the animals to determine the amount of infection and to evaluate a new “rapid” test. Personnel from USDA, APHIS, Veterinary Services and the Texas Animal Health Commission assisted with the disposal and tissue collection. Animals were transported from the ranch to the disposal site. Temporary facilities were set up to properly handle the animals.

A “field” laboratory of sorts was set up to collect and process the necessary samples. We used some of the producer’s equipment to assist with the sample collection. Samples were initially put on a paper plate with their individual animal identification then put into prelabeled bags. We collected brain stem, retropharyngeal lymph nodes, tonsils, third eyelids, and cerebellum from each animal. The brain stem was divided to assure that the traditional IHC test and the test under evaluation could be done on the same sample.  Formalin fixed and frozen samples were collected

Four hundred seventy six animals were processed. Approximately twenty people were utilized over a three day period to complete the task. Although a lot of effort was put into the planning and preparation of the project it took a large amount of manpower. A lot of additional work went into processing indemnity papers, epidemiological traces, and cleaning and disinfection of the premises. There were 365 traces to 25 states. Tracing the high risk animals which were born in the flock will take a lot of time and effort and will very likely identify additional infected flocks.