Abstract
Scrapie is a fatal neurodegenerative disease of sheep and goats belonging to the group of Transmissible Spongiform Encephalopathy or prion diseases. The EU has adopted mandatory measures for scrapie surveillance to safeguard public and animal health because it is highly contagious and might decimate all genetic susceptible animals in affected flocks. Definite diagnosis of scrapie relies on the detection of the pathological prion protein in brain tissues and there are still no blood biomarkers available for making diagnosis in living animals that can be used for the screening of sheep in scrapie-affected flocks. Neurofilament light (NfL) protein, a valid biomarker for neuronal and axonal damages, can now be easily measured in blood by the ultra-sensitive single molecule array (Simoa) technology. Recent work reported that serum NfL is increased in neurodegenerative diseases, including human prion diseases, but no data are available for scrapie or other animal prion diseases. Here, we found that the median serum NfL concentration in scrapie animals (56.2, IQR 42.2–84.8, n = 9) was more than 15 times higher (p = 0.00084) than that found in control samples (3.4, IQR 3.0–26.3, n = 11). Moreover, serum NfL concentration in scrapie sheep with clinical signs (n = 2; 75.3, 15.7 pg/ml) did not significantly (p = 0.541; t-test) differ from scrapie animals without clinical signs (n = 7; 61.0, 10.7 pg/ml). The receiver operating characteristic (ROC) curve analysis estimated the cut-off value of 31 pg/ml serum NfL for distinguishing scrapie-infected sheep from controls. The application of this cut-off value gives an accuracy of the test of 95% (percent error of 5.23%). These data indicate that the Simoa test for serum NfL might be a useful screening method for detecting preclinical scrapie in living sheep. Finally, the preliminary data reported here need confirmation in large and more structured studies.
Highlights
Transmissible spongiform encephalopathy (TSE) or prion diseases are a group of fatal progressive neurodegenerative pathologies of humans and animals
Our data show that scrapie-affected sheep have significantly higher levels of serum Neurofilament light (NfL) than control sheep, to what has been reported for human TSEs [22,23,24,25], other patients affected by degenerative or inflammatory diseases of the nervous system [17], and experimental animal models of neurodegenerative diseases [26,27,28,29]
Contrary to what occurs in humans where Creutzfeldt–Jakob disease (CJD) is an extraordinarily rare disease [32] compared with other neurodegenerative diseases, scrapie is one of the most common neurological diseases in sheep [33,34], and veterinarians usually do not perform spinal puncture in sheep or other farm animals and lack sophisticated diagnostic tools, such as brain MRI and PET scans
Summary
Transmissible spongiform encephalopathy (TSE) or prion diseases are a group of fatal progressive neurodegenerative pathologies of humans and animals. Bovine spongiform encephalopathy (BSE), scrapie of sheep and goats, and Creutzfeldt–Jakob disease (CJD) of humans are among the most notable TSE diseases [1]. Since 2002, EU adopted mandatory measures for the TSE surveillance on small ruminants to safeguard public and animal health. More than 9 million small ruminants, 2/3 are sheep, have been tested as part of the official EU TSE surveillance (Reg. EU 999/2001) by one of the EU-approved tests and the number of tested animals in 2017 had an 8.7% (34,623 samples) increase compared with 2016
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