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Title: The placenta shed from goats with classical scrapie is infectious to goat kids and lambs

item Schneider, David
item MADSEN-BOUTERSE, SALLY - Washington State University
item Zhuang, Dongyue
item Truscott, Thomas
item DASSANAYAKE, ROHANA - Washington State University
item O'ROURKE, KATHERINE - Washington State University

Submitted to: Journal of General Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2015
Publication Date: 4/17/2015
Citation: Schneider, D.A., Madsen-Bouterse, S.A., Zhuang, D., Truscott, T.C., Dassanayake, R.P., O'Rourke, K.I. 2015. The placenta shed from goats with classical scrapie is infectious to goat kids and lambs. Journal of General Virology. doi: 10.1099/vir.0.000151.

Interpretive Summary: Sheep and goats are frequently raised together and both are susceptible to the prion disease, “classical scrapie”. Lambing time is known to play a key role in natural disease transmission amongst sheep, with the shed placenta being particularly important. Goats may serve as a scrapie reservoir relevant to sheep but scientific information regarding events associated with kidding are not available. In this study, we demonstrate that the placenta shed from a goat with naturally acquired classical scrapie disease contained prions infectious to newborn sheep when exposed by the oral route. This study thus positively identifies the placenta of goats as a tissue capable of harboring prions that are infectious to sheep and by which sheep can become infected with classical scrapie by a route of natural exposure.

Technical Abstract: Classical scrapie is a natural prion disease of sheep in which the immediate postpartum period and, in particular, the placenta have long been known to play key roles in natural horizontal transmission. Goats, too, are a natural host of classical scrapie and are frequently raised with sheep; but the potential routes of natural transmission from goats to sheep have not been studied. We have recently demonstrated that the placenta of goats with classical scrapie accumulates much less of the disease-associated prion protein, PrP-Sc, in comparison to that which accumulates in the placenta of sheep. Thus, relevant to mixed-herd management practices and scrapie-eradication efforts worldwide, we sought to determine if the placenta shed from goats contains prions infectious to sheep. In the present study, a pooled homogenate inoculum was made from cotyledons freshly collected from the placenta shed from a clinical goat with naturally-acquired classical scrapie. PrP-Sc was detected in cotyledons by western blot and ELISA analyses but was approximately 300-fold less concentrated than that detected in the donor goat brain. Four recipient lambs were homozygous for the scrapie-susceptible allele coding for valine at codon 136. The lambs were derived from a scrapie-free source flock, at 48-72 hour of age were inoculated per os with the equivalent of 3-4 grams cotyledon tissue, and were hand-raised in an isolation facility. Standard antemortem biopsy and PrP-Sc immunohistochemistry were used to monitor progression of infection. PrP-Sc was not detected in biopsies of the rectal mucosa at 6 months of age but was detected in one lamb by 12 months of age. Important to the management of mixed-herds and scrapie-eradication programs, this finding confirms that the placenta of goats with classical scrapie, despite rather sparse accumulation of PrP-Sc, can contain prions that are infectious to susceptible sheep when exposed by a likely and natural route.