Scrapie

Scrapie is a transmissible spongiform encephalopathy (TSE) that predominantly impacts sheep and goats. It has been extensively studied since its discovery. BioVenic is a well-known company that specializes in researching animal diseases and providing diagnostic solutions. We have been leading the charge in contributing to the understanding and development of effective strategies to combat scrapie.

Etiology of Scrapie

Scrapie has two forms, classic and atypical. Importantly, it is not a zoonotic disease and does not spread from animals to humans.

Classic scrapie can affect sheep and goats of young and old and is characterized by both vertical (from mother to offspring) and horizontal transmission. On the other hand, atypical scrapie occurs spontaneously in older sheep. It is important to note that atypical scrapie has limited transmissibility compared to classic scrapie.

Pathogenesis

Classic scrapie is caused by the misfolding of the prion protein (Pr^Pc into PrP^sc), which causes plaque to build up in the nervous system. PrP^sc in atypical scrapie is found in lymphoid tissue. These misfolded prion proteins induce the conversion of normal proteins into the pathological isoform, resulting in the progressive degeneration of neural tissues. Despite significant research efforts, the precise mechanisms behind prion replication and transmission in scrapie remain a subject of ongoing investigation.

Fig. 1 Schematic representation of PrP^Sc deposition in goat brain.¹

Scrapie Distribution

Classic pruritus is generally accepted to occur outside of Australia and New Zealand, while atypical pruritus is accepted to occur globally. While its prevalence may vary between countries, scrapie remains a concern due to its potential economic impact and animal welfare considerations. Vigilant monitoring and surveillance are crucial to detect and manage scrapie outbreaks effectively.

Genetics

Genetic susceptibility plays an important role in the development of scrapie. Specific variants at codons 136, 154, and 171 of the sheep PRNP gene and codons 142, 146, and 22 of the goat PRNP gene are associated with susceptibility. BioVenic has contributed to the development of genetic assay methods to identify animals at risk, allowing for targeted control strategies.

Signs and Symptoms of Scrapie

The incubation period of classic scrapie is typically 2-5 years. Sheep usually die within 6 months of clinical symptoms. The clinical signs of scrapie manifest gradually, often leading to a protracted course of the disease. Initially, affected animals may exhibit behavioral changes such as increased nervousness and itching. As the disease progresses, weight loss, ataxia, and pruritus become more pronounced. In sheep and goats with atypical scrapie, pruritus is typically absent.

Transmission

• Scrapie transmission primarily occurs through the ingestion of contaminated materials, including placental tissues, birth fluids, and infected tissues.
• Horizontal transmission can occur when infected animals come into direct contact with susceptible ones.
• Importantly, scrapie is not known to infect humans, and it remains specific to sheep and goats.

Diagnosis of Scrapie

In traditional scrapie diagnosis, brain and lymph samples are collected and abnormal prion proteins are identified using immunohistochemistry (IHC), Western blot, and ELISA. Improvements have made it possible to test this by aspirating a small amount of lymphatic tissue from the third eyelid. There is no doubt that BioVenic relies on its professional capabilities to develop complete diagnostics methods and kits for customers, as well as various reagents used in diagnostics processes. Our diagnostics development involves a variety of technologies from immunodiagnostics to molecular diagnostics that help customers identify the disease faster and more reliably.

Treatment of Scrapie: Current Challenges

Currently, there are no known treatments or cures for scrapie. The degenerative nature of the disease and the complexity of prion protein replication pose significant challenges in developing therapeutic interventions. Research efforts at BioVenic and other institutions continue to explore potential treatment avenues, aiming to alleviate the suffering caused by scrapie.

Control and Prevention of Scrapie

A holistic approach, including surveillance, identification, and control measures, is essential for effectively combating scrapie. BioVenic actively contributes to national and international scrapie eradication programs and recommends the following measures:

• Combine genetic testing to identify susceptible animals and weed out animals that carry disease-associated genes.
• Using advanced methods to breed sheep that are genetically more resistant to scrapie.
• Some traditionally inspired sheep or goat products are prohibited.
• The importation and exportation of live animals, semen, and embryos must comply with strict regulations.

BioVenic continues to conduct research and development to gain a deeper understanding of scrapie and develop innovative solutions in preventing the disease. To effectively manage scrapie and maintain the health and welfare of livestock, we assist customers in developing improved diagnostics solutions and vaccines and exploring potential treatments. If you would like more information, please feel free to contact us for assistance.

References

1. Salvesen, Øyvind, et al. "Goats naturally devoid of PrPC are resistant to scrapie." Veterinary research 51.1 (2020): 1-14.