Failure to prevent classical scrapie after repeated decontamination of a barn.

Objective: Prions, the causative agent of scrapie in sheep, are extremely resistant to disinfection and can remain biologically active for years, which makes it challenging to prevent re-infection of susceptible animals on farms after a scrapie outbreak. The present study investigated the effectiveness of disinfection of a barn that previously housed scrapie-affected sheep as part of the husbandry of scrapie infected sheep on the farm. The barn was decontaminated with sodium hypochlorite for four times the recommended exposure time. Two cohorts, consisting of 25 and 21 sheep, with susceptible prion protein genotypes (VRQ/VRQ), born 2 years apart, were housed in the barn and infection monitored by examination of rectal biopsies.

Results: One sheep from the first cohort and four from the second were found to be infected from 775 (first cohort) and 550 days (second cohort) post exposure. It is concluded that decontamination with sodium hypochlorite at the recommended concentration and longer exposure time did not prevent re-infection of susceptible sheep. Disinfection of contaminated premises to eradicate scrapie continues to be a challenge.