Refining ante mortem diagnosis of classical scrapie: a case report

Introduction: Classical scrapie in sheep and goats is a notifiable disease of particular economic concern because of its ability to be transmitted within sheep and the risk of spread if undetected. Many countries rely on reporting of clinical suspects only, which requires familiarity with clinical signs, and promising ante-mortem tests are not yet validated or utilised in field situations.

Objective: To aid in the antemortem diagnosis of classical scrapie in a 24-month-old field suspect sheep using current diagnostic tools.

Methods: Clinical examinations identified published clinical markers for scrapie diagnosis. The prion protein genotype at codons 136, 154 and 171 of the sheep was determined and a rectal biopsy examined by immunohistochemistry. Scrapie status was confirmed by immunohistochemistry and Western immunoblot.

Results/Discussion: The predominant clinical signs were pruritus, a positive scratch test and tremor, which were clinical markers associated with scrapie. The sheep’s prion protein genotype was VRQ/VRQ associated with high classical scrapie susceptibility and may explain the young age of the suspect. Scrapie-associated prion protein was detected in the rectal biopsy, which was consistent with the peripheral spread of prions in this genotype. Time from first visit to diagnosis in a rectal biopsy was three weeks. The postmortem tests confirmed the antemortem diagnosis of scrapie. The inclusion of ultrasensitive prion detection tests may be a future prospect of refining the antemortem diagnosis.

Conclusion: A combination of clinical and laboratory tests resulted in a reliable antemortem diagnosis within a short period of time in a reported scrapie field suspect.