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Title: EXPERIMENTAL TRANSMISSION OF SCRAPIE TO CATTLE.

Author
item Cutlip, Randall
item Miller, Janice
item RACE, RICHARD - NIH, HAMILTON, MT.
item JENNY, ALLEN - NVSL, APHIS, AMES, IA
item Lehmkuhl, Howard
item Robinson, Mark

Submitted to: International Workshop on Bovine Spongiform Encephalopathy
Publication Type: Proceedings
Publication Acceptance Date: 2/27/1994
Publication Date: N/A
Citation: N/A

Interpretive Summary: Scrapie is a disease of the nervous system of sheep and goats that takes years for clinical signs to develop after initial infection. Because of the extraordinarily long incubation period, scrapie and related diseases are known as "slow diseases". Scrapie is the model of a group of diseases called "transmissible spongiform encephalopathies" (TSE's) of humans and animals. In sheep, progressive signs of brain disease lead to death in 1-6 months. Signs may or may not result from infection. Scrapie has been known in Europe for more than 250 years. The disease was first recognized in the United States in 1947. From 1947 to 1989, scrapie was diagnosed in 505 flocks; incidence has increased 30% in the last 10 years. This increase and epidemiologic evidence that bovine spongiform encephalopathy (BSE) in Great Britain was acquired through feeding rendered by-products of sheep to cattle caused great concern in the livestock and related industries in the United States. Therefore, this project was undertaken to determine if the U.S. scrapie agent(s) would transmit to cattle and cause a BSE-like disease. Cattle inoculated into the brain died 1-2 years after receiving the agent; clinical signs and lesions were unlike BSE. Cattle given the agent orally are alive and healthy 4.5 years after exposure. This is preliminary evidence that the U.S. scrapie agent does not cause BSE and is being so treated by the sheep and cattle industries, therefore relieving concerns about a BSE outbreak in the United States originating from sheep.

Technical Abstract: The devastating disease, bovine spongiform encephalopathy (BSE), in Great Britain is believed to have been transmitted from sheep to cattle through feeding rendered sheep by-products contaminated with the agent of scrapie. This project was undertaken to determine if the U.S. scrapie agent(s) would transmit to cattle and cause a disease resembling BSE. Groups of young male calves were intracerebrally or orally inoculated with a pooled suspension of raw brain from sheep with scrapie or fed rendered by-product prepared from sheep with scrapie in the flock. Progressive signs of neurologic disease, including stiffness, lethargy, incoordination, and decreased appetite were seen in all calves that were inoculated intracerebrally and held for more than one year after inoculation. Calves that were inoculated orally or fed rendered by-product remain normal 4.5 years after exposure. There was no evidence of aggressiveness, hyperexcitability, hyperesthesia (tactile or auditory) or hypermetria of limbs as has been reported for BSE. Microscopic examination of sections of the brain from affected calves did not reveal the primary lesions reported for BSE. All affected calves had PrP-res in brain tissue but PrP was not demonstrated in brains of calves that were exposed orally to either raw brain or rendered product. Two years after inoculation of mice, isolation of infectious agent has been successful only from the brain of one intracerebrally inoculated calf.