Scrapie in Sheep Flashcards

Question	Answer		Article
What is a prion (PrP)?	A prion (PrP) is a protein that occurs normally in the nervous and lymphoreticular tissues. When it changes conformation (PrPsc/PrPRes) it becomes an infectious agent and causes degeneration of neurological tissue.		Link to Article
What species are affected by scrapie?	Sheep Goats		Link to Article
Is scrapies a zoonosis?	Unlike BSE there is no evidence to prove that scrapie is a risk to human health. It is however notifiable.		Link to Article
What is the incubation time of scrapie?	2-5 years		Link to Article
What age does scrapie normally affect sheep?	3-5 years old		Link to Article
What is the pathogenesis of scrapie?	After ingestion, PrPsc first accumulates in Peyer’s patches of the small intestine, gut-associated lymphoid tissues (GALT) and ganglia of the enteric nervous system. It then spreads throughout the lymph nodes, tonsils, spleen, and into the peripheral nervous tissue. It is finally found in the brain several months later. The disease causes astrocyte proliferation and then vacuolization of neurons but demyelination does not occur.		Link to Article
What are the clinical signs of scrapie?	Subtle behavioural and neurological changes Fixed gaze Bruxism, fine tremors, and hyperaesthesia to sound or sudden movements Exercise intolerant and develop progressive ataxia (difficulty in turning, swaying on their hind hindquarters and have gait abnormalities such as a high stepping gait in the forelimbs or a bunny hopping gait in the hind limbs) Intense pruritis ( compulsive rubbing, nibbling at the skin, or scraping against fixed objects) Wool loss is typically seen over the hindquarters and lateral thorax Lip smacking or nibbling reflex can often be elicited by scratching over the lumbar region, which is characteristic of scrapie. Significant weight loss with or without a decrease in appetite Weakness, recumbency, and death in the later stages		Link to Article
How can scrapies be diagnosed?	PrPSc can be isolated from brainstem or lymphoid tissues by Western immunoblot, immunohistochemistry (IHC) and Elisa tests Immunohistochemistry usually shows vacuolation and an accumulation of prion proteins in various parts of the CNS (medulla, pons, midbrain, and spinal cord). However vacuolation is not completely diagnostic since it may also be present to a lesser extent in the brains of healthy sheep IHC staining of tonsil and lymphoid biopsies have been used for preclinical scrapie testing Third eyelid lymphoid tissue can be used for diagnosis in sheep.		Link to Article
What are the differential diagnosis for scrapie in sheep?	Viral encephalomyelitides (pseudorabies or Aujeszky’s disease Rabies Maedi visna Bacterial meningoencephalomyelitides (listeriosis) Pregnancy toxemia (ketosis) Hypocalcemis-hypomagnesemia Toxins (mercury, lead, organophosphates, plant toxins) Mange, lice, bacterial dermatitis		Link to Article
Can scrapie in sheep be treated?	No, scrapie is a fatal condition and no effective treatment is currently available.		Link to Article
Which allele confers the most resistance to scrapie?	The ARR allele on the PrP gene.		Link to Article
How can scrapie be controlled ?	Good husbandry and hygiene around lambing can greatly reduce the infectious load. Using individual straw bale pens which can be destroyed after each lambing Contaminated bedding and placenta should be removed immediately Maintaining a closed flock Obtaining replacement ewes or breeding rams from scrapie-free flocks. Animals of resistant genotypes should be used for breeding to further minimize the risk of scrapie infection in a flock		Link to Article