Background:

Scrapie is a fatal degenerative disease of the central nervous system of sheep and goats that was first reported in European flocks more than 250 years ago. It has since been documented throughout most of the sheep producing world. The first reported case of Scrapie in this country occurred in Michigan in 1947 and has since been diagnosed in over 650 flocks located in 42 states.

Scrapie belongs to a group of related, yet poorly understood, neurological diseases collectively known as the transmissible spongiform encephalopathies (TSEs). Spongiform encephalopathy is a descriptive term that refers to the characteristic sponge-like microscopic appearance of affected brain tissue. Diseases associated with the TSE group include Scrapie, Bovine Spongiform Encephalopathy (BSE or "mad cow disease"), which affects cattle; Transmissible Mink Encephalopathy; Feline Spongiform Encephalopathy; Chronic Wasting Disease affecting mule deer and elk; and three rare human diseases known as: Kuru, Creutzfeldt-Jakob Disease (CJD) and Gerstmann-Sträussler-Scheinker (GSS) syndrome. Due to their infrequent occurrence, undetermined causative agent(s), potential genetic link, long incubation period and atypical behavior; the TSEs represent one of the least understood disease entities affecting humans and animals.

Significance:

Although Scrapie is not widespread in the United States (US) sheep population, there is a need for Michigan producers to assume a proactive stance on the Scrapie issue. While there have been no confirmed cases of BSE in the US cattle population, the current BSE outbreak in the United Kingdom (UK) has been epidemiologically linked to Scrapie infected feed additives fed to cattle. It is speculated that changes in the rendering process enabled the Scrapie agent to survive and possibly infect cattle. Furthermore, recent events suggest a possible link between BSE and a new variant form of Creutzfeldt-Jakob Disease (V-CJD) in humans. There is a potential for a catastrophic impact on the US sheep industry if BSE is found in the US cattle population or an association between Scrapie, BSE, and V-CJD in humans is confirmed. In any event, consumer perceived associations could prove disastrous. The US sheep industry has already felt the pressure of perceived associations from the rendering industry. Surviving a unified challenge by consumers, renderers, cattle producers, public health, and state and federal regulatory agencies would be difficult for the small US sheep industry.

Seed stock producers should be aware of the importance of Scrapie as an international trade issue. The genetics found in seed stock produced by the US sheep industry has huge international marketing potential. The presence of Scrapie in the US sheep population is causing apprehension in the international marketplace. The US sheep industry recognizes the enormous potential for international sales if the Scrapie issue can be resolved. The concentration of Scrapie infected flocks in the Midwest may force federal officials to develop and enforce stringent regulatory measures on the US sheep industry. A proactive stance by the US sheep industry may deter such stringent measures. Development and implementation of the MSRRP offers a regionalized risk assessment based program that will benefit the US sheep industry in the international marketplace.

Rationale for an Innovative Michigan Scrapie Control Program:

The MSRRP allows Michigan sheep producers to participate in a unique Scrapie control program utilizing genetic selection to address Scrapie. The MSRRP was developed by a committee of producers, scientists, and state regulatory officials based on the following objectives:

• be practical,
• be flexible,
• be based on the best available science,
• be producer friendly,
• be effective in reducing the disease.

In this country, scientific information on genetic testing and selection for Scrapie resistance is devoted predominately to black-faced breeds of sheep. These are also the breeds that are the majority of the confirmed Scrapie infected sheep. As more genetic testing data become available, the genetic resistance factor may be demonstrated in other breeds.

The MSRRP will be adaptable to new science as it becomes available. The MSRRP, in its effort to accumulate scientific information, has created a pilot program to facilitate the collection of genetic information about non-black faced breeds.

Recently, genetic researchers discovered several genes that appear to play a role in resistance or susceptibility of sheep to Scrapie infection. Genetic testing ultimately allows producers a means of determining which animals in their flocks are potentially susceptible or resistant to Scrapie. Using this genetic tool, producers will be able to select breeding stock which will ultimately produce a Scrapie resistant flock. Recent tests that utilize eyelid lymphoid tissue may hold promise as a diagnostic tool and deserve continued monitoring. This, as well as future advances, will continue to be explored. International trade and consumer food safety concerns will be addressed by a practical, scientifically-based Scrapie control program.