Report of outbreaks of classical scrapie in Dorper sheep and associated prion protein gene polymorphisms in affected flocks

Abstract

Scrapie is an infectious neurodegenerative disease affecting sheep and goats, related with conformational alteration of an isoform of the prion protein that leads to deposition and aggregation in the host's central nervous system. Occurrence of the natural disease can be influenced by host genetic factors, such as a single nucleotide polymorphism of the prion protein gene. This study reports three scrapie-affected Dorper flocks located on three different farms in Brazil. The objective of this study was to analyze these three flocks using scrapie diagnostics, combining histology, immunohistochemistry, genotyping, and western blot assays. For immunohistochemistry, 192 sheep were selected and 308 sheep blood samples were taken for genotyping. A total of 22 sheep were scrapie positive by immunohistochemistry. Of these, four presented clinical signs and had scrapie immunoreactivity at the obex in western blot assays. The sheep without clinical signs were positive in lymphoid organs, such as the third eyelid and rectal mucosa. The major genotypes found on the flocks were ARQ/ARQ, ARQ/ARR, and ARQ/VRQ for codons 136, 154, and 171. Most of the sheep were considered to be at moderate to high risk, based on risk groups for developing scrapie. Some blood samples were sequenced, and polymorphisms were identified in other codons, such as 127, 142, and 143. Our data demonstrate the importance of preclinical scrapie diagnosis in Brazilian sheep, as most of the affected sheep showed no clinical signs, and emphasize the relevance of genotyping other Dorper sheep to determine the genotypic profile of the breed.

Scrapie Resistance Gene Identification using Optimized Taqman Test qPCR Method in Sheep on the Territory of the Republic of Serbia

“…Atypical scrapie is not an infectious disease and appears sporadically as a degenerative brain disease in elderly sheep [6]. Susceptibility to classical scrapie is associated with valine (V), arginine (R) and glutamine (Q) on codons 136, 154 and 171 respectively, while alanine (A), histidine (H) and arginine (R) on the same codons provide resistance [8,10,11]. The most common haplotypes are ARR, ARQ, AHQ, ARH and VRQ [12].…”

Identification of single nucleotide polymorphisms in the prion protein gene in Santa Ines and Dorset sheep

“…At these three codons, sheep with an ARR/ARR genotype are considered the most resistant to infection whereas the VRQ/VRQ genotype is considered the most susceptible. In Brazil, cases of scrapie have been observed in the Hampshire Down, Suffolk, Dorper, and Santa Ines sheep breeds, (so-called "face-black" breeds), which predominantly exhibited susceptible genotypes (Passos et al 2008, Andrade et al 2011, 2015, Ianella et al 2012. In a genotyping study of 58 scrapie-free Santa Ines sheep in Brazil, approximately 50% of the herd was considered susceptible to scrapie (Lima et al 2007).…”