The Oral Secretion of Infectious Scrapie Prions Occurs in Preclinical Sheep with a Range of PRNP Genotypes

Abstract

Preclinical sheep with the highly scrapie-susceptible VRQ/VRQ PRNP genotype secrete prions from the oral cavity. In order to further understand the significance of orally available prions, buccal swabs were taken from sheep with a range of PRNP genotypes and analyzed by serial protein misfolding cyclic amplification (sPMCA). Prions were detected in buccal swabs from scrapie-exposed sheep of genotypes linked to high (VRQ/VRQ and ARQ/VRQ) and low (ARR/VRQ and AHQ/VRQ) lymphoreticular system involvement in scrapie pathogenesis. For both groups, the level of prion detection was significantly higher than that for scrapie-resistant ARR/ARR sheep which were kept in the same farm environment and acted as sentinel controls for prions derived from the environment which might contaminate the oral cavity. In addition, sheep with no exposure to the scrapie agent did not contain any measurable prions within the oral cavity. Furthermore, prions were detected in sheep over a wide age range representing various stages of preclinical disease. These data demonstrate that orally available scrapie prions may be a common feature in sheep incubating scrapie, regardless of the PRNP genotype and any associated high-level accumulation of PrP Sc within lymphoreticular tissues. PrP Sc was present in buccal swabs from a large proportion of sheep with PRNP genotypes associated with relatively low disease penetrance, indicating that subclinical scrapie infection is likely to be a common occurrence. The significance of positive sPMCA reactions was confirmed by the transmission of infectivity in buccal swab extracts to Tg338 mice, illustrating the likely importance of orally available prions in the horizontal transmission of scrapie.

Rapid Antemortem Detection of CWD Prions in Deer Saliva

“…Several studies indicate that the concentration of prions in excreta is very low, thus requiring multiple rounds of amplification in PMCA as well as sample dilution to escape inhibitors [10,29,49,50]. Because RT-QuIC methodology offers the advantages of single cycle amplification, it offers potential for high through-put and reduced contamination risk-advantages for both detection and surveillance in the natural setting and in controlled longitudinal studies of prion pathogenesis and excretion.…”

Prion in Saliva of Bovine Spongiform Encephalopathy–Infected Cattle

“…Infectivity of saliva was demonstrated in deer with chronic wasting disease (3) and in scrapieaffected sheep (4); the immunolabeled PrP Sc accumulated in the salivary glands of scrapie-affected sheep (5). A low level of PrP Sc was detected in concentrated buccal swab samples of preclinical scrapie-infected sheep by using sPMCA (6,7). These results suggest that small amounts of PrP Sc may accumulate in the salivary glands and are then secreted into saliva.…”

Prion and prion-like diseases in animals

“…Besides, the presence of scrapie infectivity in blood (Bannach et al, 2012;Dassanayake et al, 2011Dassanayake et al, , 2012Lacroux et al, 2012), saliva (Gough et al, 2011;Tamguney et al, 2012), milk (Ligios et al, 2011) and colostum (Konold et al, 2013) in conjunction with the high resistance of this prion agent against denaturizing factors contributes to its permanency in the environment, i.e. in soil (Saunders et al, 2012b), and consequently favors the horizontal transmission within sheep and goats herds.…”