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.
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.
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 pruritus ( 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
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.