Circulation of Nor98 Atypical Scrapie in Portuguese Sheep Confirmed by Transmission of Isolates into Transgenic Ovine ARQ-PrP Mice.

Mafalda Casanova,Paula Tavares,Martin H Groschup,João Silva,Christine Fast,Leonor Orge,Carla Machado,Anne Balkema-Buschmann

doi:10.3390/ijms221910441

Abstract

Portugal was among the first European countries to report cases of Atypical Scrapie (ASc), the dominant form of Transmissible Spongiform Encephalopathy (TSE) in Portuguese small ruminants. Although the diagnostic phenotypes observed in Portuguese ASc cases seem identical to those described for Nor98, unequivocal identification requires TSE strain-typing using murine bioassays. In this regard, we initiated characterization of ASc isolates from sheep either homozygous for the ARQ genotype or the classical scrapie-resistant ARR genotype. Isolates from such genotypes were transmitted to TgshpXI mice expressing ovine PrPARQ. Mean incubation periods were 414 ± 58 and 483 ± 107 days in mice inoculated with AL141RQ/AF141RQ and AL141RR/AL141RR sheep isolates, respectively. Both isolates produced lesion profiles similar to French ASc Nor98 ‘discordant cases’, where vacuolation was observed in the hippocampus (G6), cerebral cortex at the thalamus (G8) level, cerebellar white matter (W1) and cerebral peduncles (W3). Immunohistochemical PrPSc deposition was observed in the hippocampus, cerebellar cortex, cerebellar white matter and cerebral peduncles in the form of aggregates and fine granules. These findings were consistent with previously reported cases of ASc Nor98 transmitted to transgenic TgshpXI mice, confirming that the ASc strain present in Portuguese sheep corresponds to ASc Nor98.

Highlights

Scrapie belongs to a group of diseases called transmissible spongiform encephalopathies (TSEs) or prion diseases
Four out of the initial 30 animals died less than 100 days post-inoculation and were excluded from analysis
Three of these mice had been inoculated with the ARR isolate and one mouse inoculated with the ARQ isolate

Summary

Introduction

Scrapie belongs to a group of diseases called transmissible spongiform encephalopathies (TSEs) or prion diseases. While PrPC is completely hydrolyzed by proteinase K, PrPSc has a proteinase K-resistant core (PrPres), constituting the diagnostic hallmark of transmissible prion diseases. There are two known forms of scrapie infecting small ruminants, classical scrapie (CSc) and atypical scrapie (ASc). CSc is a transmissible form of scrapie that was first diagnosed nearly 300 years ago [6]. V136R154Q171 and A136R154Q171 sheep are the most susceptible genotypes, whereas A136R154R171 and A136H154Q171 are associated with relative resistance to the disease [7]. ASc has been reported in older sheep and in sheep with the prnp CSc-resistant AHQ and ARR alleles, as well as the AF141RQ allele [8,9,10]. ASc tends to disseminate poorly within a flock [1,12]

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